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\begin{document}
\thispagestyle{plain}
\title{Examples for gWidgets}

\author{John Verzani, \url{gWidgetsRGtk@gmail.com}}
\maketitle

%% Sweave stuff
\SweaveOpts{keep.source=TRUE}

\section*{Abstract:}
[This was updated last for \pkg{gWidgets\_0.0-41}.]\\

Examples for using the \pkg{gWidgets} package are presented.  The
\pkg{gWidgets} API is intended to be a cross platform means within an
R session to interact with a graphics toolkit.  Currently, the API can
be used through:
\begin{itemize}
\item \pkg{gWidgetsRGtk2} for \pkg{RGtk2} package which is the most
  complete implementation.
\item \pkg{gWidgetstcltk} for the \pkg{tcltk} package which is the
  easiest to install (for windows users) but not as fully implemented
  or polished.
\item \pkg{gWidgetsQt} for the \pkg{qtbase} package. This package
  allows the Qt toolkit to be used from within R. It is being
  developed and is available from r-forge.
\item \pkg{gWidgetsrJava} for the \pkg{rJava} package. This
  package may be deprecated in the near term if no interest is shown.
\end{itemize}


The \pkg{gWidgetsWWW} package is an independent implementation for web programming.
It uses the EXT JS JavaScript libraries to provide R to web
interactivity. It leverages the \pkg{rapache} package for server
installs, and has a user-only web browser leveraged from the
\pkg{Rpad} package. Unlike the other implementations, this package is
stand alone and does not use \pkg{gWidgets} itself.


% Finally, a partial port for the \pkg{RwxWidgets} package is started,
% but awaits completion of that package.

The API is intended to facilitate the task of writing basic GUIs, as
it simplifies many of the steps involved in setting up widgets and
packing them into containers. Although not nearly as powerful as any
individual toolkit, the \pkg{gWidgets} API is suitable for many
tasks or as a rapid prototyping tool for more complicated
applications. The examples contained herein illustrate that quite a
few things can be done fairly easily with more complicated
applications being pieced together in a straightforward manner.  To
see a fairly complicated application built using \pkg{gWidgets},
install the \pkg{pmg} GUI
(\url{http://www.math.csi.cuny.edu/pmg}), which is on CRAN.


The \pkg{traitr} package implements a model-view-controller
programming style for GUI development. It uses \pkg{gWidgets} to
provide the GUI components.

%\setcounter{tocdepth}{3}
%\tableofcontents

\section{Background}
The \code{gWidgets} API is intended to be a cross-toolkit API for
working with GUI objects. It is based on the iwidgets API of Simon
Urbanek, with improvements suggested by Philippe Grosjean, Michael Lawrence,
Simon Urbanek and John Verzani.  This document focuses on the more
complete toolkit implementation provided by the
\pkg{gWidgetsRGtk2} package.~\footnote{Occasional differences with
\pkg{gWidgetsQt}, \pkg{gWidgetstcltk}, or \pkg{gWidgetsrJava} are pointed out
in braces. The major differences from the \pkg{gWidgets} API are
documented in the help files given by the package name, e.g. \pkg{gWidgetstcltk}} The GTK toolkit is interfaced via the \pkg{RGtk2}
package of Michael Lawrence, which in turn is derived from Duncan
Temple Lang's \pkg{RGtk} package. The excellent \pkg{RGtk2}
package opens up the full power of the GTK2 toolkit, only a fraction
of which is available though \pkg{gWidgetsRGtk2}.

The \code{gWidgets} API is mostly stable, but does occasionally have
additional methods and constructors added. If a feature seems lacking,
please let the author know.

\section{Overview}

The basic tasks in setting up a GUI involve: constructing the desired
widgets, laying these widgets out into containers, and assigning
handlers to respond to user-driven events involving the widgets. The
\pkg{gWidgets} package is geared around these tasks, and also around providing a
familiar means to interact with the widgets once constructed.  The
actual toolkits have much more flexibility during the layout of the
GUI and afterwards in pragmatically interacting with the GUI.  Each
widget constructor in \pkg{gWidgets} includes the arguments
\code{container} to specify a parent container to place it in;
\code{handler}, to specify a handler to respond to the main event
that the widget has; and \code{action}, which is used to pass extra
information along to any handler. Each widget when constructed returns
an object of S4 class which can be manipulated using generic
functions, some new and some familiar.

The basic widgets are likely familiar: buttons, labels, text-edit areas,
etc. In addition, there are some R-specific compound widgets such as a
variable browser, data frame viewer, and help viewer. In contrast to
these, are a few basic dialogs, which draw their own window and are
modal, hence do not return objects which can be manipulated.

The examples below introduce the primary widgets, containers, and
dialogs in a not-so systematic manner, focusing instead on some
examples which show how to use \pkg{gWidgets}. The man pages are
also a source information about the widgets, see \code{?gWidgets} for
more detail. For differences between the toolkit implementation, see
the man page for the package name, for example,
\code{?gWidgetstcltk}.

This document is a vignette. As such, the code displayed is available
within an R session through the command
\code{edit(vignette("gWidgets"))}. 

\section{Installation}

In case you are reading this vignette without having installed
gWidgets, here are some instructions focusing on installing
\pkg{gWidgetsRGtk2}. 

More details are found at the \pkg{gWidgets} website \url{http://www.math.csi.cuny.edu/pmg/gWidgets}.

Installing \code{gWidgets} with the \code{gWidgetsRGtk2} package
requires two steps: installing the GTK libraries and installing the R
packages.



\subsection{Installing the GTK libraries}

The \code{gWidgetsRGtk2} provides a link between \code{gWidgets} and
the GTK libraries through the \code{RGTk2} package.  \texttt{RGtk2}
requires relatively modern versions of the GTK libraries (2.8.12 is suggested).
These may need to be installed or upgraded on your system.

In case of \textbf{Windows} you can do this:

\begin{enumerate}
\item 
 Download the files from
\href{http://gladewin32.sourceforge.net/modules/wfdownloads/visit.php?lid=102}{http://gladewin32.sourceforge.net/modules/wfdownloads/visit.php?lid=102}

\item run the resulting file.  This is an automated installer which will walk
you through the installation of the Gtk2 libraries.
\end{enumerate}

For Windows users, the following command, will do this and install
\code{pmg}. (Likely you are better off with the previous method.)
\begin{Sinput}
> source("http://www.math.csi.cuny.edu/pmg/installPMG.R")
\end{Sinput}


In Linux, you may or may not need to upgrade the GTK libraries
depending on your distribution. If you have a relatively modern
installation, you should be ready.

For Mac OS X there is also a packaged port of the GTK run time libraries available
through at \url{http://r.research.att.com/}. 



When the author used this quite some time ago, the
\pkg{cairoDevice} package failed (this may be fixed by now). As such, the
the macports (\url{http://www.macports.org}) project was used to
install its \texttt{gtk2} package. Once macports is installed, the command
\begin{verbatim}
sudo port install gtk2
\end{verbatim}
will install the libraries (although it may take quite a while).


There are more details on RGtk2 at 
\href{http://www.ggobi.org/rgtk2}{RGtk2's home page}.


\subsection{Install the R packages}

The following R packages are needed: \texttt{RGtk2},
\texttt{cairoDevice}, \texttt{gWidgets}, and
\texttt{gWidgetsRGtk2}. Install them in this order, as some depend on
others to be installed first. All can be downloaded from CRAN.

These can all be installed by following the dependencies for
\code{gWidgetsRGtk2}. The following command will install them all if
you have the proper write permissions:

\begin{verbatim}
   install.packages("gWidgetsRGtk2", dep = TRUE)
\end{verbatim}

It may be necessary  to adjust the location where the libraries will be
installed if you do not have the proper permissions.

For MAC OS X, the source packages might be desired if you installed
via macports, not the default
``mac.binary.'' Use the \code{type=} argument, as follows:
\begin{verbatim}
> install.packages("gWidgetsRGtk2", dep = TRUE,type = "source" )
\end{verbatim}

% On occasion, newer versions are available from
% \href{http://www.math.csi.cuny.edu/pmg}{gWidgets's website}. To
% install from here add the \texttt{repos=} argument, as follows:

% \begin{verbatim}
% > install.packages("gWidgetsRGtk2",dep = TRUE, repos = "http://www.math.csi.cuny.edu/pmg")
% \end{verbatim}

[The \pkg{gWidgetsQt} package requires the \pkg{qtbase} package which
is not yet on CRAN, but rather is installed through r-forge.]

[The \pkg{gWidgetstcltk} requires the 8.5 version of tcl/tk which
comes with the windows version of R as of 2.7.0, but typically needs
to be installed manually for linux and mac machines, as of this writing.]

[The \pkg{gWidgetsrJava} package is installed similarly. However,
it requires \pkg{rJava}. These should install through the dependencies, so
\begin{verbatim}
> install.packages("gWidgetsrJava", dep = TRUE)
\end{verbatim}
should do it. The \pkg{rJava} has some potential issues with the mac version of
R that can arise if R is compiled from source.]

[The \pkg{gWidgetsWWW} package is altogether different. The package
requires \pkg{rapache} to be installed to be used in server mode. As
well, the apache web server must also be configured.
The package can be used locally through a standalone web server.
]


\section{Loading gWidgets}
We  load the \code{gWidgets} package, using the \code{gWidgetsRGtk2}
toolkit, below:
following 



<<>>=
require(gWidgets)
options("guiToolkit"="RGtk2")
@
<<echo=FALSE>>=
require(gWidgetsRGtk2)
@ 

When \code{gWidgets} is started, it tries to figure out what its
default toolkit will be. In this examples, we've set it to be
``gWidgetsRGtk2.'' If the option was not set and there is more than
one toolkit available, then a menu asks the user to choose between
toolkit implementations. 


[For \pkg{gWidgetsQt} use ``Qt'', for \pkg{gWidgetsrJava} use ``rJava''
in the \RFunc{options} call or ``tcltk'' for the
\pkg{gWidgetstcltk} package.]

[The \pkg{gWidgetsWWW} package is different, as it doesn't use the
\pkg{gWidgets} package for dispatch. It is loaded directly via
\code{require(gWidgetsWWW, quietly=TRUE)} -- using the \code{quietly} switch, as
anything output to STDOUT is sent to the browser.]

\section{Hello world}

We begin by showing how to make various widgets which display the
ubiquitous ``Hello world'' message. 



\begin{figure}[htbp]
  \centering
  \begin{tabular}{l@{\quad}l}
  \includegraphics[width=.35\textwidth]{button}&
  \includegraphics[width=.35\textwidth]{label}\\
  \includegraphics[width=.35\textwidth]{radio}&
  \includegraphics[width=.35\textwidth]{droplist}
  \end{tabular}
  \caption{Four basic widgets: a button, a label, radio buttons, and a drop list.}
  \label{fig:basic-widgets}
\end{figure}


Now to illustrate (Figure~\ref{fig:basic-widgets} shows a few) some of
the basic widgets.  These first widgets display text: a label, a
button and a text area.


First a button:
<<>>=
  obj <- gbutton("Hello world", container = gwindow())
@

Next a label:
<<>>=
  obj <- glabel("Hello world", container = gwindow())  
@

Now for single line of editable text:
<<>>=
  obj <- gedit("Hello world", container = gwindow())
@

Finally, a text buffer for multiple lines of text:
<<>>=
  obj <- gtext("Hello world", container = gwindow())
@

The following widgets are used for selection of a value or values from
a vector of possible values.

First a radio group for selecting just one of several:
<<>>=
  obj <- gradio(c("hello","world"), container=gwindow())
@

Next, combo box, (was called a droplist) again for selecting just one
of several, although in this case an option can be give for the user
to edit the value.
<<>>=
  obj <- gcombobox(c("hello","world"), container=gwindow())
@

A combo box can also allow its value to be entered by typing,
<<>>=
  obj <- gcombobox(c("hello","world"), editable=TRUE, container=gwindow())
@


For longer lists, a table of values can be used.
<<>>=
  obj <- gtable(c("hello","world"), container=gwindow())
@
This widget is also used for displaying tabular data with multiple
columns and rows (data frames).  For this widget there is an argument
allowing for multiple selections. Multiple selections can also be achieved
with a checkbox group:

<<>>=
  obj <- gcheckboxgroup(c("hello","world"), container=gwindow())
@



For selecting a numeric value from a sequence of values, sliders and
spinbuttons are commonly used:
<<>>=
  obj <- gslider(from=0, to = 7734, by =100, value=0,
    container=gwindow())
  obj <- gspinbutton(from=0, to = 7734, by =100, value=0, 
   container=gwindow())
@

Common to all of the above is a specification of the ``value'' of the
widget, and the container to attach the widget to. In each case a
top-level window constructed by \RFunc{gwindow}.

\subsection{Using containers}

In this next example, we show how to  combine widgets together using
containers. (Figure~\ref{fig:hello-world}.)


<<>>=
  win <- gwindow("Hello World, ad nauseum", visible=TRUE)
  group <- ggroup(horizontal = FALSE, container=win)
  obj <- gbutton("Hello...",container=group, 
    handler = function(h,...) gmessage("world"))
  obj <- glabel("Hello...", container =group, 
    handler = function(h,...) gmessage("world"))
  obj <- gcombobox(c("Hello","world"), container=group)
  obj <- gedit("Hello world", container=group)
  obj <- gtext("Hello world", container=group, font.attr=list(style="bold"))
@


As before, the constructors \RFunc{gbutton}, \RFunc{glabel},
\RFunc{gedit} and \RFunc{gtext} create widgets of different
types~\footnote{We refer to \code{gbutton} as a constructor, which it
  is, and also a widget class, which it technically isn't.}.
The button looks like a button. A label is used to show text which may
perhaps be edited. [Editing text isn't implemented in all toolkits. and in
personal experience seems to be confusing to users.] A combobox allows a user to select one of several
items, or as illustrated can take user input. The \RFunc{gedit} and
\RFunc{gtext} constructors both create widgets for inputting text, in
the first case for single lines, and in the second for multiple lines
using a text buffer.

\begin{figure}[htbp]
  \centering
  \includegraphics[width=.35\textwidth]{hello-world}
  \caption{Hello world example}
  \label{fig:hello-world}
\end{figure}

These widgets are packed into containers (see \code{?ggroup} or
\code{?gwindow}). The base container is a window, created with the
\RFunc{gwindow} function. A top-level window only contains one widget,
like a group, so we pack in a group container created with
\RFunc{ggroup}. (Top-level windows also may contain menubars, toolbars
and statusbars.) The \RFunc{ggroup} container packs in widgets from
left to right or top to bottom. Imagine each widget as a block which
is added to the container.  In this case, we want the subsequent
widgets packed in top to bottom so we used the argument
\code{horizontal=FALSE}.

For the button and label widgets, a  handler is set so that when the widget is
clicked a message dialog appears showing ``world.'' Handlers are used
to respond to mouse-driven events. In this case the event of a widget
being clicked. See \code{?gWidgetsRGtk-handlers} for details on
handlers. 

Note the handler has signature \code{(h,...)} where \code{h} is a list
with components \code{obj} referring to the widget the handler is
called on, \code{action} referring to the value passed to the
\RArg{action} argument and perhaps others (eg. \code{dropdata} for
drag-and-drop events, and \code{x} and \code{y} for \code{ggraphics}
click events.). The \code{...} in the signature, may contain
information passed along by the underlying toolkit and is necessary
but not generally employed.

The message is an instance of a ``basic dialog'' (see
\code{?gWidgets-dialogs}). The dialogs in \code{gWidgets} are
modal, meaning R's event loop is stopped until the dialog is answered.
(This can be annoying if a dialog appears under another
window and can't be seen!) As such, they don't return an object which
has methods defined for it, as by the time they can be accessed they
have been dismissed. Instead, they return a value like a logical or a string.


\section{Making a confirmation dialog}

Let's see how we might use widgets to create our own confirmation
dialog, one which is not modal. We want to have an icon, a label for
the message, and buttons to confirm or dismiss the dialog.

The \RFunc{gimage} constructor allows images to be shown in a
widget. In \pkg{gWidgetsRGtk} there are several stock images, which can be
listed with \RFunc{getStockIcons}. We will use ``info'' below.

First we define a function for making a dialog. This one uses
nested group containers to organize the layout. (Alternately the
\RFunc{glayout} constructor could have been used in some manner.)

<<>>=
confirmDialog <- function(message, handler=NULL)  {
  window <- gwindow("Confirm")
  group <- ggroup(container = window)
  gimage("info", dirname="stock", size="dialog", container=group)

  ## A group for the message and buttons
  inner.group <- ggroup(horizontal=FALSE, container = group)
  glabel(message, container=inner.group, expand=TRUE)

  ## A group to organize the buttons
  button.group <- ggroup(container = inner.group)
  ## Push buttons to right
  addSpring(button.group)
  gbutton("ok", handler=handler, container=button.group)
  gbutton("cancel", handler = function(h,...) dispose(window),
          container=button.group)
  
  return()
}
@

The key to making a useful confirmation dialog is attaching a response
to a click of the ``ok'' button. This is carried out by a handler,
which are added using the argument \RArg{handler} for the constructor,
or with one of the \code{addHandlerXXX} functions. The handler below prints
a message and then closes the dialog. To close the dialog, the
\RFunc{dispose} method is called on the ``ok'' button widget, which is
referenced inside the handler by \code{h\$obj} below. In
\code{gWidgets}, handlers are passed information via the first
argument, which is a list with named elements. The \RListel{obj}
component refers to the widget the handler is assigned to.

Trying it out produces a widget like that shown in
Figure~\ref{fig:confirmDialog}

\begin{figure}[htbp]
  \centering
  \includegraphics[width=.35\textwidth]{confirmDialog}
  \caption{Confirmation dialog}
  \label{fig:confirmDialog}
\end{figure}

<<>>=
confirmDialog("This space for rent", handler = function(h,...) {
  print("what to do... [Change accordingly]")
  ## In this instance dispose finds its parent window and closes it
  dispose(h$obj)
})
@
%%$

\section{Methods}

Widgets are interacted with by their methods. The main methods are
\RFunc{svalue} and \RFunc{svalue<-} for getting and setting a widgets
primary value. 

The following silly example illustrates how clicking one widget can be
used to update another widget.
<<>>=
w <- gwindow("Two widgets")
g <- ggroup(container = w)
widget1 <- gbutton("Click me to update the counter", container=g, 
                   handler = function(h,...) {
                     oldVal <- svalue(widget2)
                     svalue(widget2) <- as.numeric(oldVal) + 1
                   })
widget2 <- glabel(0, container=g)
@
The value stored in a label is just the text of the label. This is
returned by \RFunc{svalue} and after 1 is added to the value, replaced
back into the label. As text labels are of class ``character,'' the
value is coerced to be numeric.

There are other methods (see \code{?gWidgetsRGtk-methods}) that try to
make interacting with a widget as natural (to an R user) as
possible. For instance, a radio button has a selected value returned
by \RFunc{svalue}, but also a vector of possible values. These may be
referenced using vector, \code{[}, notation. Whereas, a notebook
container has a \RFunc{names} method which refers to the tab labels,
which may be set via \code{names<-} and a \RFunc{length} method to
return the number of notebook pages.

\section{Adding a GUI to some common  tasks}

A GUI can make some command line tasks easier to perform. Here are a
few examples that don't involve much coding in \code{gWidgets}.

\subsection{\RFunc{file.choose}}
The \RFunc{file.choose} function is great for simplifying a user's
choice of a file from the file system. A typical usage might be
\begin{Soutput}
  source(file.choose())
\end{Soutput}
to allow a user to source a file with a little help from a
GUI. However, in many UNIX environments, there is no GUI for
\RFunc{file.choose}, only a more convenient curses interface.  With
the \RFunc{gfile} dialog, we can offer some improvement.

This dialog returns the name of the file selected, so that
\begin{Soutput}
  source(gfile())
\end{Soutput}
can replace the above.


More in keeping with the \code{gWidgets} style, though, would be to
give a handler when constructing the file chooser. The \code{file}
component of the handler argument gives the files name (not
\code{svalue(h\$obj)}, as \code{gfile} does not return an object to
call \code{svalue} on). For example, the function below is written to
give some flexibility to the process:
%%$

<<>>=
fileChoose <- function(action="print", text = "Select a file...",
                       type="open", ...) {
  gfile(text=text, type=type, ..., action = action, handler =
        function(h,...) {
          do.call(h$action, list(h$file))
        })
}
@

The \RArg{action} argument parametrizes the action. The default above
calls \RFunc{print} on the selected file name, hence printing the
name. However, other tasks can now be done quite simply. For example,
to \RFunc{source} a file we have:

%% not in <<>>=/@ as they are modal and mess up Sweave
\begin{Sinput}
> fileChoose(action="source")
\end{Sinput}

Or to set the  current working directory we have:
\begin{Sinput}
> fileChoose(action="setwd", type="selectdir", text="Select a directory...")
\end{Sinput}

\subsection{\RFunc{browseEnv}}
\label{sec:browseEnv}

The \RFunc{browseEnv} function creates a table in a web browser
listing the current objects in the global environment (by default)
and details some properties of them. This is an easy to use function,
but suffers from the fact that it may have to open up a browser for
the user if none is already open. This may take a bit of time as
browsers are generally slow to load. We illustrate a means of using
the \RFunc{gtable} constructor to show in a table the objects in an
environment.

The following function creates the data.frame we will display. Consult the code
of \RFunc{browseEnv} to see how to produce more details.

<<>>=
lstObjects <- function(envir= .GlobalEnv, pattern) {
  objlist <- ls(envir=envir, pattern=pattern)
  objclass <- sapply(objlist, function(objName) {
    obj <- get(objName, envir=envir)
    class(obj)[1]
  })
  data.frame(Name = I(objlist), Class = I(objclass))
}
@

Now to make a table to display the results. We have some flexibility
with the arguments, which is shown in subsequent examples:


<<>>=
browseEnv1 <- function(envir = .GlobalEnv, pattern) {
  listOfObjects <- lstObjects(envir=envir, pattern)
  gtable(listOfObjects, container = gwindow("browseEnv1"))
}
@

Tables can have a double click handler (typically a single click is used for
selection). To illustrate, we  add a handler which 
calls \RFunc{summary} (or some other function) on a double-clicked
item [Qt's behaviour is OS dependent].
(The first \code{svalue} returns a character string, it is promoted
to an object using \code{get})
<<>>=
browseEnv2 <- function(envir = .GlobalEnv, pattern, action="summary") {
  listOfObjects <- lstObjects(envir=envir, pattern)
  gtable(listOfObjects, container = gwindow("browseEnv2"),
         action = action, 
         handler = function(h,...) {
           print(do.call(h$action, list(get(svalue(h$obj)))))
         })
}
@

As a final refinement, we  add a combobox to filter by the unique
values of ``Class.'' We leave as an exercise the display of icons
based on the class of the object.
<<>>=
browseEnv3 <- function(envir = .GlobalEnv, pattern, action="summary") {
  listOfObjects <- lstObjects(envir=envir, pattern)
  gtable(listOfObjects, 
         container =gwindow("browseEnv3"),
         filter.column = 2,
         action = action, 
         handler = function(h,...) {
           print(do.call(h$action, list(get(svalue(h$obj)))))
         })
}
@
[The \code{filter} argument is not available with \pkg{gWidgetsrJava}
or \pkg{gWidgetsWWW}.]

In \pkg{gwidgetsRGtk2} The \RFunc{gvarbrowser} function constructs a
widget very similar to this, only it uses a \RFunc{gtree} widget to allow
further display of list-like objects. [The \code{gtree} widget is not
implemented in all of the toolkits.]


\section{A gWidgetsDensity demo}
\label{sec:repeating-plot}

We illustrate how to make a widget dynamically update a density
plot. The idea comes from the \code{tkdensity} demo that accompanies
the \pkg{tcltk} package due to, I believe, Martin Maechler.

We use the  \RFunc{ggraphics} constructor to create a new plot device. For
RGtk2, this uses the \pkg{cairoDevice} package also developed
by Michael Lawrence. (This package takes some work to get going under
OS X, as the easy-to-install RGtk2 libraries don't seem to like the package.)

[In \pkg{gWidgetsrJava} the \pkg{JavaGD} package is used for
a JAVA device. In theory this should be embeddable in a \pkg{gWidgets}
container, but it isn't implemented, so a new window is created.]

[In \pkg{gWidgetstcltk} there is no embeddable graphics
device. (The \pkg{tkrplot} is different.) The \code{ggraphics}
call would just put in a stub.]

This demo consists of a widget to control a random sample, in this case
from the standard normal distribution or the exponential distribution
with rate 1; a widget to select the sample size; a widget to select the
kernel; and a widget to adjust the default bandwidth. We use radio
buttons for the first two, a drop list for the third and a slider for
the latter.


The \pkg{gWidgetstcltk} package is a little different from the
other two, as it requires that a container be non-null. This is
because the underlying \pkg{tcltk} widgets need to have a parent
container to be initialized. As such, the following won't work. A
working example will be given next for comparison. This one is left
here, as the separation  of GUI building into: widget definition;
widget layout; and assignment of handlers, or call backs, seems to
lead to easier to understand code.

Proceeding, first we define the two distributions and the possible kernels.
<<setUp>>=
## set up
availDists <- c(Normal="rnorm", Exponential="rexp")
availKernels <- c("gaussian", "epanechnikov", "rectangular",
                  "triangular", "biweight", "cosine", "optcosine")
@

We then define the key function for drawing the graphic. This refers
to widgets yet to be defined.
                      
<<updatePlot>>=
updatePlot <- function(h,...) {
  x <- do.call(availDists[svalue(distribution)],list(svalue(sampleSize)))
  plot(density(x, adjust = svalue(bandwidthAdjust), 
               kernel = svalue(kernel)),main="Density plot")
  rug(x)
}
@
Now to define the widgets.
<<define.widgets>>=
distribution <- gradio(names(availDists), horizontal=FALSE, handler=updatePlot)
kernel <- gcombobox(availKernels, handler=updatePlot)
bandwidthAdjust <- gslider(from=0,to=2,by=.01, value=1, handler=updatePlot)
sampleSize <- gradio(c(50,100,200, 300), handler = updatePlot)
@

Now the layout. We use frames to set off the different arguments. A
frame is like a group, only it has an option for placing a text label
somewhere along the top. The position is specified via the \code{pos}
argument, with a default using the left-hand side.
<<layout>>=
## now layout
window <- gwindow("gWidgetsDensity")
BigGroup <- ggroup(cont=window)

group <- ggroup(horizontal=FALSE, container=BigGroup)
tmp <- gframe("Distribution", container=group)
add(tmp, distribution)

tmp <- gframe("Sample  size", container=group)
add(tmp,sampleSize)

tmp <- gframe("Kernel", container=group)
add(tmp,kernel)

tmp <- gframe("Bandwidth adjust", container=group)
add(tmp,bandwidthAdjust, expand=TRUE)
@

Now to add a graphics device.
\begin{Soutput}
> add(BigGroup, ggraphics())
\end{Soutput}
[Again, if using \RFunc{gWidgetsrJava} this wouldn't place the device
inside the \code{BigGroup} container.]

A realization of this widget was captured in Figure~\ref{fig:gtkdensity}.

\begin{figure}
  \centering
  \includegraphics[width=.6\textwidth]{gtkdensity}
  \caption{The gWidgetsDensity example in action.}
  \label{fig:gtkdensity}
\end{figure}


Now, as promised, we present a function that would work under any of
the toolkits. The \code{ggraphics} call is not included, as this
doesn't work with \pkg{gWidgetstcltk}. The key difference though
is the containers are included in the creation of the widgets. The
arguments that would be passed to \code{add} are included in the
construction of the widget.

<<gwtkdensity>>=
gwtkdensity <- function() {

  ## set up
  availDists <- c(Normal = "rnorm", Exponential="rexp")
  availKernels <- c("gaussian", "epanechnikov", "rectangular",
                    "triangular", "biweight", "cosine", "optcosine")
  
  
  updatePlot <- function(h,...) {
    x <- do.call(availDists[svalue(distribution)],list(svalue(sampleSize)))
    plot(density(x, adjust = svalue(bandwidthAdjust), kernel = svalue(kernel)))
    rug(x)
  }
  
  ##The widgets
  win <- gwindow("gwtkdensity")
  gp <- ggroup(horizontal=FALSE, cont=win)
  
  tmp <- gframe("Distribution", container=gp, expand=TRUE)
  distribution <- gradio(names(availDists), horizontal=FALSE,
                         cont=tmp, 
                         handler=updatePlot)
  
  
  tmp <- gframe("Sample  size", container=gp, expand=TRUE)
  sampleSize <- gradio(c(50,100,200, 300), cont=tmp,
                       handler =updatePlot)
  
  
  tmp <- gframe("Kernel", container=gp, expand=TRUE)
  kernel <- gcombobox(availKernels, cont=tmp,
                      handler=updatePlot)
  
  tmp <- gframe("Bandwidth adjust", container=gp, expand=TRUE)
  bandwidthAdjust <- gslider(from=0,to=2,by=.01, value=1,
                             cont=tmp, expand=TRUE,
                             handler=updatePlot)
  
}
@



\section{Composing email}

This example shows how to write a widget for composing an email
message. Not that this is what R is intended for, but rather to show
how a familiar widget is produced by combining various pieces from
\code{gWidgets}. This example is a little lengthy, but hopefully
straightforward due to the familiarity with the result of the task.

For our stripped-down compose window we want the following: a menubar
to organize functions; a toolbar for a few common functions; a ``To:''
field which should have some means to store previously used e-mail addresses; a
``From:'' field that should be editable, but not obviously so as often
it isn't edited; a ``Subject:'' field which also updates the title of
the window; and a text buffer for typing the message.

The following code will create a function called \RFunc{Rmail}
(apologies to any old-time emacs users) which on many UNIX machines can
send out e-mails using the \code{sendmail} command.

This is not written to work with \code{gWidgetstcltk}.


First we define some variables:
<<buddyList>>=
FROM <- "gWidgetsRGtk <gWidgetsRGtk@gmail.com>"
buddyList <- c("My Friend <myfriend@gmail.com>","My dog <mydog@gmail.com>")
@

Now for the main function. We define some helper functions inside the
body, so as not to worry about scoping issues.
<<Rmail>>=
Rmail <- function(draft = NULL, ...) {
  ## We use a global list to contain our widgets
  widgets <- list()
  
  
  ## Helper functions
  sendIt <- function(...) {
    tmp <- tempfile()
    
    cat("To:", svalue(widgets$to),"\n",file = tmp, append=TRUE)
    cat("From:", svalue(widgets$from),"\n", file=tmp, append=TRUE)
    cat("Subject:", svalue(widgets$subject),"\n", file=tmp, append=TRUE)
    cat("Date:", format(Sys.time(),"%d %b %Y %T %Z"),"\n", file=tmp, append=TRUE)
    cat("X-sender:", "R", file=tmp, append=TRUE)
    cat("\n\n", file=tmp, append=TRUE)
    cat(svalue(widgets$text), file=tmp, append=TRUE)
    cat("\n", file=tmp, append=TRUE)
    
    ## Use UNIX sendmail to send message
    system(paste("sendmail -t  <", tmp))
    ## Add To: to buddyList
    if(exists("buddyList"))
      assign("buddyList", unique(c(buddyList,svalue(widgets$to))), inherits=TRUE)
    
    ## Close window, delete file
    unlink(tmp)
    dispose(window)
  }
  
  ## Function to save a draft to the file draft.R
  saveDraft <- function(...) {
    draft <- list()
    sapply(c("to","from","subject","text"), function(i) 
           draft[[i]] <<- svalue(widgets[[i]])
           )
    dump("draft","draft.R")
    cat("Draft dumped to draft.R\n")
  }
  
  ## A simple dialog
  aboutMail <- function(...) gmessage("Sends a message")
  
  ## Make main window from top down
  
  window <- gwindow("Compose mail")
  group <- ggroup(horizontal=FALSE, spacing=0, container = window)
  ## Remove border
  svalue(group) <- 0
  
  actions <- list(save=gaction("Save", icon="save", handler=saveDraft),
                  send=gaction("Send", icon="connect", handler=sendIt),
                  quit=gaction("Quit", icon="quit", handler=function(...) dispose(window)),
                  about=gaction("About", icon="about", handler=aboutMail))
  
  ## Menubar is defined by the actions, but we nest under File menu
  menubarlist <- list(File=actions)
  gmenu(menubarlist, cont = window)
  
  ## Toolbar is also defined by the actions
  toolbarlist <-  actions[-4]
  gtoolbar(toolbarlist, cont=window)
  
  
  ## Put headers in a glayout() container
  tbl <- glayout(container = group)
  
  
  ## To: field. Looks for buddyList
  tbl[1,1] <- glabel("To:",container = tbl)
  tbl[1,2] <- (widgets$to <- gcombobox(c(), editable=TRUE, container=tbl))
  if(exists("buddyList")) widgets$to[] <- buddyList
  
  ## From: field. Click to edit value
  tbl[2,1] <- glabel("From:", container = tbl)
  tbl[2,2] <- (widgets$from <- glabel(FROM, editable=TRUE, container=tbl))
  
  ## Subject: field. Handler updates window title
  tbl[3,1] <- glabel("Subject:")
  tbl[3,2] <- (widgets$subject <- gedit("",container=tbl))
  addHandlerKeystroke(widgets$subject, handler = function(h,...)
                      svalue(window) <- paste("Compose mail:",svalue(h$obj),collapse=""))
  
  ## Add text box for message, but first some space
  addSpace(group, 5)
  widgets$text <- gtext("", container = group, expand=TRUE)


  ## Handle drafts. Either a list or a filename to source")
  ## The generic svalue() method makes setting values easy")
  if(!is.null(draft)) {
    if(is.character(draft))
      sys.source(draft,envir=environment()) # source into right enviro
    if(is.list(draft)) {
      sapply(c("to","from","subject","text"), function(i) {
        svalue(widgets[[i]]) <- draft[[i]]
      })
    }
  }

  ## That's it.

}

@
%%$

To compose an e-mail we call the function as follows. (The widget constructed looks like Figure~\ref{fig:Rmail}.)
<<comd>>=
  Rmail()
@

\begin{figure}[htbp]
  \centering
  \includegraphics[width=.5\textwidth]{Rmail}
  \caption{Widget for composing an e-mail message. (Needs a grammar checker.) }
  \label{fig:Rmail}
\end{figure}

The \RFunc{Rmail} function uses a few  tricks.  A combobox is
used to hold the ``To:'' field. This is done so that a ``buddy list''
can be added if present. The \code{[<-} method for comboboxes make
this straightforward. For widgets that have a collection of items to
select from, the vector and matrix methods are defined to make
changing values familiar to R users. (Although the use of
the method \code{[<-}  for \code{glayout} containers can cause confusion, as
no \code{[} method exists due to the indexing referring to coordinates
and not indexes.)

The ``From:'' field uses an editable label. Clicking in the label's
text allows its value to be changed. Just hit ENTER when
done.~\footnote{Editable labels seemed like a good idea at the time --
  they were borrowed from gmail's interface -- but in experience they
  seem to be confusing to users. YMMV.}

The handler assigned to the ``Subject:'' field updates the window
title every keystroke. The title of the window is updated with the windows
\RFunc{svalue<-} method.

The \RFunc{svalue} and \RFunc{svalue<-} methods are the work-horse
methods of \code{gWidgets}. The are used to retrieve the selected
value of a widget or set the selected value of a widget. One advantage
to have a single generic function do this is illustrated in the
handling of a draft:
\begin{Soutput}
 sapply(c("to","from","subject","text"), function(i)
   svalue(widgets[[i]]) <- draft[[i]])
\end{Soutput}

(Another work-horse method is \RFunc{addHandlerChanged} which can be
used to add a handler to any widget, where ``changed'' -- being a
generic function -- is loosely
interpreted: i.e., for buttons, it is aliased to
\RFunc{addHandlerClicked}.

As for the \RFunc{sendIt} function, this is just one way to send an
e-mail message on a UNIX machine. There are likely more than 100
different ways clever people could think of doing this task, most better than
this one.

To make portable code, when filling in the layout container, the
widget constructors use the layout container as the parent container
for the new widget.



\section{An expanding group}
As an example of the \code{add} and \code{delete} methods of a
container, we show how one could create the \code{gexpandgroup}
widget, were it not implemented by the underlying toolkit
(eg. \pkg{gWidgetstcltk}). This container involves an icon to
click on to show the container and a similar icon to hide the
container. A label indicates to the user what is going on.
<<expandgroup>>=
  ## expand group
  rightArrow <- system.file("images/1rightarrow.gif",package="gWidgets")
  downArrow <- system.file("images/1downarrow.gif",package="gWidgets")


  g <- ggroup(horizontal=FALSE,cont=T)
  
  g1 <- ggroup(horizontal=TRUE, cont=g)
  icon <- gimage(downArrow,cont=g1)
  label <- glabel("Expand group example", cont=g1)
  
  g2 <- ggroup(cont=g, expand=TRUE)
  
  expandGroup <- function() add(g,g2, expand=TRUE)
  hideGroup <- function() delete(g,g2)
  
  state <- TRUE                            # a global
  
  changeState <- function(h,...) {
    if(state) {
      hideGroup()
      svalue(icon) <- rightArrow
    }  else {
      expandGroup()
      svalue(icon) <- downArrow
    }
    state <<- !state
  }

addHandlerClicked(icon, handler=changeState)
addHandlerClicked(label, handler=changeState)

gbutton("Hide by clicking arrow", cont=g2)
  
@
%%>>

As an alternative to using the global \code{state}  variable, the
\RFunc{tag} function could be used. This is like \RFunc{attr} only it
stores the value with the widget -- not a copy -- so can be used
within a handler to propogate changes outside the scope of the handler
call. For instance, the \code{changeState} function could
have been written as
<<>>=
tag(g,"state") <- TRUE                            # a global
changeState <- function(h,...) {
  if(tag(g,"state")) {
    hideGroup()
    svalue(icon) <- rightArrow
  }  else {
    expandGroup()
    svalue(icon) <- downArrow
  }
  tag(g,"state") <- !tag(g,"state")
}
@

Other alternatives to using global variables include using
environments or the \pkg{proto} package for \code{proto} objects. These
objects are passed not by copy, but by reference so changes within a
function are reflected outside the scope of the function.


\section{Drag and drop}
GTK supports drag and drop features, and the \code{gWidgets} API provides a
simple mechanism to add drag and drop to widgets. (Some widgets, such
as text boxes, support drag and drop without these in GTK.) The basic
approach is to add a drop source to the widget you wish to drag from,
and add a drop target to the widget you want to drag to. You can also
provide a handler to deal with motions over the drop target. See the
man page \code{?gWidgetsRGtk-dnd} for more information.

[In \pkg{gWidgetsQt} drag and drop support is very limited.]

[In \pkg{gWidgetsrJava} drag and drop is provided through Java
and not \pkg{gWidgets}. One can drag from widget to widget, but
there is no way to configure what happens when a drop is made, or what
is dragged when a drag is initiated.]

[In \pkg{gWidgetstcltk} drag and drop works but not from other
applications. 
]


We give two examples of drag and drop. One where variables from the
variable browser are dropped onto a graph widget. Another illustrating
drag and drop from the data frame editor to a widget.

\subsection{DND with plots}


This example shows the use of the plot device, the variable browser
widget, and the use of the drag and
drop features of gWidgets (Figure~\ref{fig:doPlot}).



<<>>=
doPlot <-  function() {
  ## Set up main group
  mainGroup <- ggroup(container=gwindow("doPlot example"))
    
  ## The variable browser widget
  gvarbrowser(container = mainGroup)

  rightGroup <- ggroup(horizontal=FALSE, container=mainGroup)
    
  ## The graphics device
  ggraphics(container=rightGroup)
  entry <- gedit("drop item here to be plotted", container=rightGroup)
  adddroptarget(entry,handler = function(h,...) {
    do.call("plot",list(svalue(h$dropdata),main=id(h$dropdata)))
  })
}
@
%%$
<<>>=
 doPlot()
@ 


\begin{figure}[htbp]
  \centering
  \includegraphics[width=.6\textwidth]{doPlot.png}
  \caption{Dialog produced by \RFunc{doPlot} example}
  \label{fig:doPlot}
\end{figure}

The basic structure of using \code{gWidgets} is present in this
example. The key widgets are the variable browser
(\RFunc{gvarbrowser}), the plot device (\RFunc{ggraphics}), and the
text-entry widget (\RFunc{gedit}). (One can see an \pkg{RGtk2}
bias here, as the other implementations do not currently have an embeddable graphics
device.) These are put into differing
containers.  Finally, there is an handler given to the result of the
drag and drop. The \RFunc{do.call} line uses the \RFunc{svalue} and
\RFunc{id} methods on a character, which in this instance returns the
variable with that name and the name.


To use this widget, one drags a variable to be plotted from the
variable browser over to the area below the plot window. The
\RFunc{plot} method is called on the values in the dropped variable.


The \code{gvarbrowser} produces a widget from which a drop
\textit{source} has been added. To drop from a different source the
\code{addDropSource} method is used. The return value of the handler
will be passed to the \code{dropdata} value of the handler for
\code{addDropTarget}. 

[The latter varies from toolkit to toolkit, in
\pkg{gWidgetsrJava} both are ignored, in RGtk2 some widgets have
built-in drag and drop which can be overridden, and in \pkg{gWidgetstcltk}
everything must be done using the \pkg{gWidgets} interface, as drag and drop
is not naturally implemented by the toolkit.]

\subsection{DND from the data frame editor}

[This example applies only to \pkg{gWidgetsRGtk}, not
\pkg{gWidgetsrJava} or \pkg{gWidgetstcltk}]


The \RFunc{gdf} constructor makes a widget for editing data
frames. The columns of which can be dropped onto a widget. This is 
done by dragging the column header. The code below also adds a handler
so that changes to the column propagate to changes in the widget where
the column is dropped. (Careful, this has some issues: the handler needs to
be removed if the widget is closed.)

<<>>=
## Drag a column onto plot to have a boxplot drawn.
## Changing the column values will redraw the graph.

makeDynamicWidget <-  function() {
  
  win <- gwindow("Draw a boxplot")
  gd <- ggraphics(container = win)
  
  adddroptarget(gd, targetType="object", handler=function(h,...) {
    tag(gd,"data") <- h$dropdata
    plotWidget(gd)
    
    ## this makes the dynamic part:
    ## - we put a change handler of the column that we get the data from
    ## - we store the handler id, so that we can clean up the handler when this
    ##   window is closed
    
    ## The is.gdataframecolumn function checks if the drop value
    ##   comes from the data frame editor (gdf)
    if(gWidgetsRGtk2:::is.gdataframecolumn(h$dropdata)) {
      view.col <- h$dropdata
      
      ## Put change handler on column to update plotting widget
      ## (use lower case, to fix oversight)
      id <- addhandlerchanged(view.col, handler=function(h,...) plotWidget(gd))
      ## Save drop handler id so that it can be removed when
      ##   widget  is closed
      dropHandlers <- tag(gd,"dropHandlers")
      dropHandlers[[length(dropHandlers)+1]] <- 
        list(view.col = view.col,
             id = id
             )
      tag(gd,"dropHandlers") <- dropHandlers
    }
  })
  
  ## Remove drop handlers if widget is unrealized.
  addHandlerUnrealize(gd, handler = function(h,...) {
    dropHandlers <- tag(gd,"dropHandlers")
    if(length(dropHandlers) > 0) {
      for(i in 1:length(dropHandlers)) {
        removehandler(dropHandlers[[i]]$view.col,dropHandlers[[i]]$id)
      }
    }
  })
}
@
%% $

Next, we make the function that produces or updates the graphic. The
data is stored in the tag-key "data". The use of \RFunc{id} and
\RFunc{svalue} works for values which are either variable names or columns.

<<>>=
plotWidget <- function(widget) {
  data <- tag(widget, "data")
  theName <- id(data)
  values <- svalue(data)
  boxplot(values, xlab=theName, horizontal=TRUE, col=gray(.75))
}
@

Now show the two widgets, the \RFunc{gdf} function constructs the data
frame editor widget.

<<>>=
gdf(mtcars, container=TRUE)
makeDynamicWidget()
@ 
%%$


\section{Notebooks}

The notebook is a common metaphor with computer applications, as they
can give access to lots of information compactly on the screen. The
\RFunc{gnotebook} constructor produces a notebook widget. New pages
are added via the \RFunc{add} method (which is called behind the
scenes when a widget is constructed), the current page is deleted
through an icon [not implemented in \pkg{gWidgetsrJava}], or via
the \RFunc{dispose} method, and vector methods are defined, such as
\RFunc{names}, to make interacting with notebooks natural (the names
refer to the tab labels.) One can also add pages when constructing a
widget using the notebook as the container and passing in an extra
argument \code{label}.

The following example shows how a notebook can be used to organize
different graphics devices. 

[In \pkg{gWidgetsRGtk2} the
\RFunc{ggraphicsnotebook} function produces a  similar
widget. However, this is not possible if using
\pkg{gWidgetsrJava}, as the graphic devices can't currently be
embedded in a notebook page.]

Our widget consists of a toolbar to add or delete plots and a notebook
to hold the different graphics devices. The basic widgets are defined
by the following:

First we make window and group containers to hold our widgets and then
a notebook instance.
<<>>=
win <- gwindow("Plot notebook")
group <- ggroup(horizontal = FALSE, container=win)
nb <- gnotebook(container = group, expand=TRUE)
@
(\code{expand=TRUE} causes the child widget -- the notebook -- to
expand to take as much space as allotted.)

Next, we begin with an initial plot device.
\begin{Soutput}
> ggraphics(container = nb,  label="plot")
\end{Soutput}
The \code{label} argument goes on the tab, as it is passed to the
notebook's \code{add} method.



Now we define and add a toolbar. 
<<>>=
tblist <- list(quit=gaction("Quit", icon="quit", handler=function(...) dispose(win)),
               separator=gseparator(),
               new=gaction("New", icon="new", handler=function(h,...) add(nb,ggraphics(),label="plot")),
               delete=gaction("Delete", icond="delete", handler=function(...) dispose(nb))
               )

gtoolbar(tblist, cont=group)
@
The \RFunc{dispose} method is used both to close the window, and to close
a tab on the notebook (the currently selected one).


\begin{figure}[htbp]
  \centering
  \includegraphics[width=.6\textwidth]{notebook}
  \caption{Notebook widget for holding multiple plot devices provided by \RFunc{ggraphics}}
  \label{fig:notebook}
\end{figure}

That's it (Figure~\ref{fig:notebook}). There is one thing that should
be added. If you switch tabs, the active device does not switch. This
happens though if you click in the plot area. To remedy this, you can
think about the \RFunc{addHandlerChanged} method for the notebook, or
just use \RFunc{ggraphicsnotebook}.



\section{The tree widget}

The \RFunc{gtree} constructor [this widget is only implemented in
\pkg{gWidgetsRGtk2}.] is used to present tree-like data. A
familiar example of such data is the directory structure of your
computer.  To display a tree, \RFunc{gtree} needs to know what to
display (the offspring) and which offspring have further offspring.
idea of a node which consists of a path back to a root node. The
offspring are determined by a function (\RFunc{offspring}) which takes
the current path (ancestor information), and a passed in parameter as
arguments. These offspring can either have subsequent offspring or
not. This information must be known at the time of displaying the
current offspring, and is answered by a function
(\RFunc{hasOffspring}) which takes as an argument the offspring. In
our file-system analogy, \RFunc{offspring} would list the files and
directories in a given directory, and \RFunc{hasOffspring} would be
\code{TRUE} for a directory in this listing, and \code{FALSE} for a
file. For decorations, a function \RFunc{icon.FUN} can be given to
decide what icon to draw for which listing. This should give a stock
icon name.

The data presented for the offspring is a data frame, with one column
determining the path. This is typically the first column, but can be
set with \RArg{chosencol}.
\\


To illustrate, we create a file system browser using
\RFunc{gtree}. (This is for UNIX systems. change the file separator
for windows.)

First to define the \RFunc{offspring} function we use the
\RFunc{file.info} function. The current working directory is used as
the base node for the tree:

<<>>=
  ## function to find offspring
  offspring <- function(path, user.data=NULL) {
    if(length(path) > 0) 
      directory <- paste(getwd(),"/",paste(path,sep="/", collapse=""),sep="",collapse="")
    else
      directory <- getwd()
    tmp <- file.info(dir(path=directory))
    files <- data.frame(Name=rownames(tmp), isdir=tmp[,2], size=as.integer(tmp[,1]))
    return(files)
  }
@

The offspring function is determined by the \code{isdir} column in
the offspring data frame. 
<<>>=
hasOffspring <- function(children,user.data=NULL, ...) {
  return(children$isdir)
}
@

Finally, an icon function can be given as follows, again using the
\code{isdir} column.

<<>>=
icon.FUN <- function(children,user.data=NULL, ...) {
  x <- rep("file",length= nrow(children))
  x[children$isdir] <- "directory"
  return(x)
}
@

The widget is then constructed as follows. See
Figure~\ref{fig:filebrowser} for an example.
<<>>=
  gtree(offspring, hasOffspring, icon.FUN = icon.FUN,
        container=gwindow(getwd()))
@

\begin{figure}[htbp]
  \centering
  \includegraphics[width=.6\textwidth]{filebrowser}
  \caption{Illustration of a file browser using \RFunc{gtree} constructor.}
  \label{fig:filebrowser}
\end{figure}


The presence of the \code{isdir} column may bug some. It was
convenient when defining \RFunc{hasOffspring} and \RFunc{icon.FUN},
but by then had served its purpose. One way to eliminate it, is to use
the default for the \RArg{hasOffspring} argument which is to look for
the second column of the data frame produced by \RFunc{offspring}. If
this column is of class \code{logical}, it is used to define
\RFunc{hasOffspring} and is then eliminated from the display. That is,
the following would produce the desired file browser:

<<>>=
gtree(offspring,  icon.FUN = icon.FUN,
      container=gwindow(getwd()))
@

Finally, the  \RArg{handler} argument (or
\code{addHandlerDoubleclick}) could have been used to give an action to double
clicking of an item in the tree. 



\section{Popup menus}

A popup menu ``pops'' up a menu after a mouse click, typically a right
mouse click. Implemented in \pkg{gWidgets} are the functions

\begin{description}
\item[\RFunc{add3rdmousepopupmenu}] for adding a popup on a right click
\item[\RFunc{addpopupmenu}] for adding a popup on any click
\end{description}

The menu is specified using the syntax for \RFunc{gmenu}.
\\


A simple example would be something like:

<<>>=
w <- gwindow("Click on button to change")
g <- ggroup(cont = w)                   # abbreviate container
glabel("Hello ", cont=g)
world <- gbutton("world", cont=g)
lst <- list()
lst$world$handler <- function(h,...) svalue(world) <- "world"
lst$continent$handler <- function(h,...) svalue(world) <- "continent"
lst$country$handler <- function(h,...) svalue(world) <- "country"
lst$state$handler <- function(h,...) svalue(world) <- "state"
addPopupmenu(world, lst)
@
Clicking on ``world'' with the mouse allows one to change the value in
the label.

\section{Defining layouts with \RFunc{gformlayout}}

The \RFunc{gformlayout} constructor allows one to define the layout of
a GUI using a list. The details of the list are in the man page, but
the list has a relatively simple structure. Each widget is specified using
a list. The widget type is specified through the \code{type} component
as a string. These may be containers or widgets or the special
container \code{fieldset}. For containers, the component
\code{children} is used to specify the children to pack in. These
again are specified using a list, and except for the \code{fieldset}
container may again contain containers. The \code{name} argument is
used to have the newly created component stored in a list of widgets
for later manipulations. There are means to control
whether a component is enabled or not based on a previously defined
component, such as a checkbox. (This works much better under
\pkg{gWidgetsRGtk2} than \pkg{gWidgetstcltk} as disabled parent
containers do not disable their children in the latter.)

This example comes from the man page. It shows how the ``fieldset''
container is used with some of its arguments to modify the number of
columns and adjust the default label placements.

We present the final list, \code{tTest} using some predefined lists
that could be recycled for other GUIs if desired.

<<t-test-ex, keep.source=TRUE>>=
## layout a collection of widgets to generate a t.test

## widgets to gather the variable(s)
varList <- list(type="fieldset",
                columns = 2,
                label = "Variable(s)",
                label.pos = "top",
                label.font = c(weight="bold"),
                children = list(
                  list(name = "x",
                       label = "x",
                       type = "gedit",
                       text = ""),
                  list(name = "y",
                       label = "y",
                       type = "gedit",
                       text = "",
                       depends.on = "x",
                       depends.FUN = function(value) nchar(value) > 0,
                       depends.signal = "addHandlerBlur"
                       )
                       )
                )
## list for alternative
altList <- list(type = "fieldset",
                label = "Hypotheses",
                columns = 2, 
                children = list(
                  list(name = "mu",
                       type = "gedit",                            
                       label = "Ho: mu=",
                       text = "0",
                       coerce.with = as.numeric),
                  list(name = "alternative",
                       type="gcombobox",
                       label = "HA: ",
                       items = c("two.sided","less","greater")
                       )
                  )
                )
## now make t-test list
tTest <- list(type = "ggroup",
              horizontal = FALSE,
              children = list(
                varList,
                altList,
                list(type = "fieldset",
                     label = "two sample test",
                     columns = 2,
                     depends.on = "y",
                     depends.FUN = function(value) nchar(value) > 0,
                     depends.signal = "addHandlerBlur",                     
                     children = list(
                       list(name = "paired",
                            label = "paired samples",
                            type = "gcombobox",
                            items = c(FALSE, TRUE)
                            ),
                       list(name = "var.equal",
                            label = "assume equal var",
                            type = "gcombobox",
                            items = c(FALSE, TRUE)
                            )
                       )
                     ),
                list(type = "fieldset",
                     columns = 1,
                     children = list(
                       list(name = "conf.level",
                            label = "confidence level",
                            type = "gedit",
                            text = "0.95",
                            coerce.with = as.numeric)
                       )
                     )
                )
              )
@ 
<<eval=FALSE>>=
## Code to call the layout
w <- gwindow("t.test")
g <- ggroup(horizontal = FALSE, cont = w)
fl <- gformlayout(tTest, cont = g, expand=TRUE)
bg <- ggroup(cont = g)
addSpring(bg)
b <- gbutton("run t.test", cont = bg)
addHandlerChanged(b, function(h,...) {
  out <- svalue(fl)
  out$x <- svalue(out$x) # turn text into numbers
  if(out$y == "") {
    out$y <- out$paired <- NULL 
  } else {
   out$y <- svalue(out$y)
  }
  ## easy, not pretty
  print(do.call("t.test",out))
})

@ 

\section{Making  widgets from an R function}

A common task envisioned for \pkg{gWidgets} is to create GUIs
that make collecting the arguments to a function easier to remember or
enter. Presented below are two ways to do so without having to do any
programming, provided you are content with the layout and features
provided.



\subsection{Using \RFunc{ggenericwidget}}
\label{sec:using-ggenericwidget}


The \RFunc{ggenericwidget} constructor maps a list into a widget. The
list contains two types of information: meta information about the
widget, such as the name of the function, and information about the
widgets. This is specified using a list whose first component is the
constructor, and subsequent components are fed to the constructor.

To illustrate, a GUI for a one sample t-test  is given. The
list used by \RFunc{ggenericwidget}  is defined below.

<<>>=
lst <- list()
lst$title <- "t.test()"
lst$help <- "t.test"
lst$variableTypes <- "univariate"
lst$action <- list(beginning="t.test(",ending=")")
lst$arguments$hypotheses$mu <- 
  list(type = "gedit",text=0,coerce.with=as.numeric)
lst$arguments$hypotheses$alternative <- 
  list(type="gradio", items=c("'two.sided'","'less'","'greater'")
       )
@

This list is then given to the constructor.
<<>>=
ggenericwidget(lst, container=gwindow("One sample t test"))
@

Although this looks intimidating, due to the creation of the list,
there is a function \RFunc{autogenerategeneric} that reduces the work involved.
In particular, if the argument to \RFunc{ggenericwidget} is a
character, then it is assumed to be the name of a function. From the
arguments of this function, a layout is guessed.

For example, we could have done:
<<>>=
  our.t.test <- stats:::t.test.default
  ggenericwidget("our.t.test", container=gwindow("t-test"))
@
As the arguments of this function are 

<<>>=
args(our.t.test)
@

This widget has fields for selecting the alternative, the null,
whether the data is paired, has equal variance assumption and a field
to adjust the confidence level.

\subsection{An alternative to \RFunc{ggenericwidget}}
\label{sec:an-altern-ggenericwidget}

This next example shows a different (although ultimately similar) way
to produce a widget for a function. One of the points of this example
is to illustrate the power of having common method names for the
different widgets. Of course, the following can be improved. Two obvious
places are the layout of the automagically generated widget, and and
the handling of the initial variable when a formula is expected.
 
<<>>=
## A constructor to automagically make a GUI for a function
gfunction <- function(f, window = gwindow(title=fName), ...) {

  ## Get the function and its name
  if(is.character(f)) {
    fName <- f
    f <- get(f)
  } else if(is.function(f)) {
    fName <- deparse(substitute(f))
  }
    
  ## Use formals() to define the widget
  lst <- formals(f)

  
  
  ## Hack to figure out variable type
  type <- NULL
  if(names(lst)[1] == "x" && names(lst)[2] == "y") {
    type <- "bivariate"
  } else if(names(lst)[1] == "x") {
    type <- "univariate"
  } else if(names(lst)[1] == "formula") {
    type <- "model"
  } else {
    type + NULL
  }
  

  ##  Layout
  
  w <- gwindow("create dialog")
  g <- ggroup(horizontal = TRUE, cont=w)
  ## Arrange widgets with an output area
  ## Put widgets into a layout container
  tbl <- glayout(container=g)
  gseparator(horizontal=FALSE, container=g)
  outputArea <- gtext(container=g, expand=TRUE)
  

  ## Make widgets for arguments from formals()
  widgets <- sapply(lst, getWidget, cont=tbl)

  ## Layout widgets
  for( i in 1:length(widgets)) {
    tbl[i,1] <- names(lst)[i]
    tbl[i,2] <- widgets[[i]]
  }


  ## Add update handler to each widget when changed
  sapply(widgets, function(obj) {
    try(addHandlerChanged(obj, function(h,...) update()), silent=TRUE)
  })

  ## Add drop target to each widget
  sapply(widgets, function(obj)
         try(adddroptarget(obj,
                           handler=function(h,...) {
                             svalue(h$obj) <- h$dropdata
                             update()
                           }),
             silent=TRUE))
  


  ## In case this doesn't get exported
  svalue.default <- function(obj, ...) obj
  
  ## Function used to weed out 'NULL' values to widgets
  isNULL <- function(x) 
    ifelse(class(x) == "character" && length(x) ==1 && x == "NULL",
           TRUE, FALSE)
  
  ## Function called when a widget is changed
  ## 2nd and 3rd lines trim out non-entries
  update <- function(...) {
    is.empty <- function(x) return(is.na(x) || is.null(x) || x == "" )
    outList <- lapply(widgets,svalue)
    outList <- outList[!sapply(outList,is.empty)]
    outList <- outList[!sapply(outList,isNULL)]
    outList[[1]] <- svalue(outList[[1]])
    if(type == "bivariate")
      outList[[2]] <- svalue(outList[[2]])
    
    out <- capture.output(do.call(fName,outList))
    
    dispose(outputArea)
    if(length(out)>0)
      add(outputArea, out)
  }
  invisible(NULL)
}
@

The \RFunc{getWidget} function takes a value from \RFunc{formals}
and maps it to an appropriate widget. For arguments of type
\code{call} the function recurses.

<<>>=
getWidget <- function(x, cont=cont) {
  switch(class(x),
         "numeric" = gedit(x, coerce.with=as.numeric, cont=cont),
         "character" = gcombobox(x, active=1, cont=cont),
         "logical" = gcombobox(c(TRUE,FALSE), active = 1 + (x == FALSE), cont=cont),
         "name" = gedit("", cont=cont),
         "NULL" = gedit("NULL", cont=cont),
         "call" = getWidget(eval(x), cont=cont), # recurse
         gedit("", cont=cont)                     # default
    )
}
@
%% not there    "list" = gListOfWidgets(x,name="", cont=cont), 

% This function defines a separate widget to handle the case where an
% argument expects a list. It is written in the \code{gWidgetsRGtk} style
% including an \RFunc{svalue} method below. The \RFunc{tag} method stores
% a value in the widget, similar to setting an attribute. In this case,
% the list of widgets stored is consulted by the following \RFunc{svalue} method.

% <<>>=
% gListOfWidgets = function(lst, name = "",  container=NULL, ...) {
%   gp = gframe(text = name, container=container, horizontal=FALSE, ...)
%   obj = list(ref=gp)
%   class(obj) = c("gListOfWidgets")

%   tbl = glayout(container = gp)
%   widgetList = lapply(lst, getWidget, cont=tbl)
%   tag(obj, "widgetList") <-  widgetList

%   ## pack into layout
%   for(i in 1:length(widgetList)) {
%     tbl[i,1] = names(widgetList)[i]
%     tbl[i,2] = widgetList[[i]]
%   }
%   visible(tbl) <- TRUE
%   return(obj)
% }
% @

% The methods below (\RFunc{svalue}, \RFunc{svalue<-} and
% \RFunc{addHandlerChanged})  map the same method to each component
% of the list using \RFunc{sapply}.

% <<>>=
% svalue.gListOfWidgets = function(obj,  ...) {
%   lst = lapply(tag(obj, "widgetList"), svalue)
%   return(lst)
% }


% "svalue<-.gListOfWidgets" = function(obj, ..., value) {
%   if(!is.list(value))
%   return(obj)

%   widgetList = getdata(obj, "widgetList")
%   sapply(names(value), function(x) svalue(widgetList[[x]]) <- value[[x]])

%   return(obj)
% }

% addHandlerChanged.gListOfWidgets = function(obj, handler=NULL, action=NULL, ...) {
%   widgetList = getdata(obj, "widgetList")
%   sapply(widgetList, function(x)
%          try(addHandlerChanged(x, handler, action),silent=TRUE))
% }
% @

We can try this out on the default \RFunc{t.test} function. First we
grab a local copy from the namespace, then call our function. The
widget with an initial value for \code{x} is shown in
Figure~\ref{fig:gfunction}.


<<>>=
our.t.test <- stats:::t.test.default
gfunction(our.t.test)
@

\begin{figure}[htbp]
  \centering
  \includegraphics[width=.6\textwidth]{gfunction}
  \caption{Illustration of \RFunc{gfunction}}
  \label{fig:gfunction}
\end{figure}





\end{document}
