Trying to debug your own GUI applications can be a pain if you are not
extremely familiar with the toolkit used to make the user
interface. When the code you are working on is also unfamiliar, the
whole experience quickly becomes less than desirable. The GTK+ Parasite tool helps
you to work out the structure of the widgets that comprise a GUI, inspect
and change properties of those widgets, and perform more
in-depth analysis using an embedded Python shell.
The GTK+ toolkit provides an
object-oriented framework for making user interfaces in C.
GTK+ gives you facilities to inspect and change the properties of
objects and supports introspection so you don't need to know about classes
at compile time in order to make use of them at runtime. The GTK+
Parasite attaches itself to a GTK+ application and takes advantage of
these dynamic features to let you inspect and change the interface of
an application as it runs.
GTK+ Parasite doesn't have any official releases yet, but the source
can easily be pulled from its Git repository, compiled and installed
using the standard
./autogen.sh && make autotools
dance. You'll want
to make sure that you have the development packages for PyGtk
installed first in order to get the embedded Python shell
To use GTK+ Parasite, add its name to the GTK_MODULES environment
variable and run your GTK+ application as you normally would. For
Along with your application,
you should see and additional Parasite window with a Widget Tree and
Action List tab and a small area in the lower part of the window with
a Python prompt.
To find out the hierarchy of widgets in your GTK+ application, click
on the Inspect button in the Parasite window and then any part of the
GUI of your GTK+ application. Along with each widget in a tree view
you should see if that widget is realized, mapped and visible, along
with the address of both the X Window of the widget and the GTK+
widget itself. The latter address is very handy because you can right
click on it and "Send Widget to Shell" to obtain a reference to the
widget from the embedded Python interpreter.
The list in the far right of the Widget Tree tab in the Parasite
window lists the properties and their value for the current
widget. Holding the left button down over a property pops up a list of
possible values for you to change it too. On the other hand, if the
range of values for a property is too large, like for an integer
property, no menu is presented and you can enter the value directly.
The Action List tab in Parasite shows you all the GTKAction
objects in the application. For those unfamiliar with the
GTK+ toolkit, a GtkAction object represents a piece of functionality
that can be connected to a menu or toolbar, for example, opening a
Save as dialog or starting a search within the current document. As an
example, running Parasite on the text editor gedit, finding the
FileOpen action in the list and selecting "Send Object to Shell" from
the menu, you can perform the GtkAction by calling the activate method
on the object. You should see the file dialog appear. The embedded
Python shell command should look something like:
where everything up to the
.activate() was added automatically by Parasite when I told it to
send the object to the shell.
If you are writing a custom GTK widget, the "Show Graphic Updates"
button causes any redraws that the application performs to briefly
flash red first. This makes it fairly simple to see if you are drawing
more than you think in order for your widget to update
itself. For example, in gedit, only a rectangle covering the current
line is updated when you type text into the active document, but when
you hit return the current line and everything below it flashes red.
There are a few rough edges to the GUI of GTK+ Parasite, which is to be
expected from such a young application. For example, in the "Action
List" tab, one might expect to be able to simply double-click on an
action to execute it. In addition, left-clicking on a property lets you
either edit the value directly
inline in the cell or if there is a limited number of acceptable values
a popup menu appears allowing you to select a value. While this provides
a consistent user interface for editing though left clicking, it does
mean that you have to click on a property row before editing its value.
One might at first expect a context menu to be available offering such
editing functionality, with the added bonus that you could directly
right click on a property to edit it rather than having to select it
with a left click first.
For such a young application GTK+ Parasite is already
very useful and a great tool for ironing out the kinks in an
application's GTK+ interface. If you are a Python fan, the
embedded Python interpreter lets you tinker with the GTK+ interface
even if the program itself is written in C.
Parasite is developed by Christian Hammond and David Trowbridge.
Activity on the mailing list is
currently on the slow side, but it should pick up as developers
discover this tool.
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