Table of Contents
To begin our introduction to GNU Smalltalk GTK, we'll start with the simplest program possible. This program (base.st) will create a 200x200 pixel window and has no way of exiting except to be killed by using the shell.
1 #!/usr/bin/env gst 2 3 Eval [ 4 PackageLoader fileInPackage: 'GTK'. 5 window := GTK.GtkWindow new: GTK.Gtk gtkWindowToplevel. 6 window show. 7 GTK.Gtk main 8 ]
You can run the above program using:
gst base.st
If base.st is made executable
and can be found in your PATH, it can be run
using:
base.st
Line 1 will invoke GNU Smalltalk to run base.st in this
case. Line 4 loads the package GTK which contains all the classes need for creating GTK widgets. In this case the program creates
a new instance of the GtkWindow class and it then invokes the method main to start
the GTK+ event processing loop.
A window similar to Figure 2.1, “Simple GNU Smalltalk GTK Window” should popup on your display.
The first line allows the program base.st to be
invoked from a Linux or Unix shell program assuming that
GNU Smalltalk is found your PATH. This line
will be the first line in all the example programs.
Lines 4 import the GTK package and initializes the GTK+
environment. The GTK module defines the GNU Smalltalk interfaces to the GTK+
functions that will be used in the program. For those familiar with GTK+ the
initialization includes calling the gtk_init() function.
This sets up a few things for us such as the
default visual and color map, default signal handlers, and checks the
arguments passed to your application on the command line, looking for one or
more of the following:
- --gtk-module
- --g-fatal-warnings
- --gtk-debug
- --gtk-no-debug
- --gdk-debug
- --gdk-no-debug
- --display
- --sync
- --name
- --class
It removes these from the argument list, leaving anything it does not recognize for your application to parse or ignore. These are a set of standard arguments accepted by all GTK+ applications.
Line 5 creates a top level window and directs GTK+ to display it
(line 6). The GTK.GtkWindow is created in line 11 with the
argument GTK.Gtk WINDOW_TOPLEVEL that specifies that we want
the window to undergo window manager decoration and placement. Rather than
create a window of 0x0 size, a window without children is set to 200x200 by
default so you can still manipulate it.
Lines 7 calls the GTK main function that, in turn,
invokes the GTK+ main event processing loop to handle mouse and keyboard events as
well as window events. When control reaches this point, GTK+ will sleep waiting for X
events (such as button or key presses), timeouts, or file IO notifications to
occur. In our simple example, however, events are ignored.
Now for a program with a widget (a button). It's the GNU Smalltalk GTK version of the classic hello world program (helloworld.st ).
1 #!/usr/bin/env gst 2 3 " example helloworld.st" 4 5 Eval [ 6 PackageLoader fileInPackage: 'GTK'. 7 ] 8 9 Object subclass: HelloWorld [ 10 | button window | 11 12 " This is a callback function. 13 More on callbacks below. " 14 hello [ 15 'Hello World' printNl 16 ] 17 18 delete [ 19 " If you return false in the 'delete_event' signal handler, 20 GTK will emit the 'destroy' signal. Returning true means 21 you don't want the window to be destroyed. 22 This is useful for popping up 'are you sure you want to quit?' 23 type dialogs. " 24 'delete event occurred' printNl. 25 26 " Change false to true and the main window will not be destroyed 27 with a 'delete_event'." 28 ^ false 29 ] 30 31 destroy [ 32 'destroy signal occurred' printNl. 33 GTK.Gtk mainQuit 34 ] 35 36 show [ 37 " create a new window " 38 window := GTK.GtkWindow new:GTK.Gtk gtkWindowToplevel. 39 40 " When the window is given the 'delete_event' signal (this is given 41 by the window manager, usually by the 'close' option, or on the 42 titlebar), we ask it to call the delete_event function 43 as defined above. The data passed to the callback 44 function is nil and is ignored in the callback function. " 45 window connectSignal: 'delete_event' to: self selector: #delete userData: nil. 46 47 " Here we connect the 'destroy' event to a signal handler. 48 This event occurs when we call destroy on the window, 49 or if we return false in the 'delete_event' callback. " 50 window connectSignal: 'destroy' to: self selector: #destroy userData: nil. 51 52 " Sets the border width of the window. " 53 window setBorderWidth: 10. 54 55 " Creates a new button with the label 'Hello World'. " 56 button := GTK.GtkButton newWithLabel: 'Hello World'. 57 58 " When the button receives the 'clicked' signal, it will call the 59 function hello passing it None as its argument. The hello 60 function is defined above. " 61 button connectSignal: 'clicked' to: self selector: #hello userData: nil. 62 63 " This will cause the window to be destroyed by calling 64 destroy when 'clicked'. Again, the destroy signal could come from 65 here, or the window manager. " 66 button connectSignal: 'clicked' to: self selector: #destroy userData: window. 67 68 " This packs the button into the window (a GTK container). " 69 window add: button. 70 71 " The final step is to display this newly created widget. " 72 button show. 73 74 " and the window " 75 window show. 76 ] 77 ]. 78 79 " If the program is run directly or passed as an argument to the python 80 interpreter then create a HelloWorld instance and show it" 81 Eval [ 82 hello := HelloWorld new. 83 hello show. 84 " All GTK applications must have a GTK.Gtk main. Control ends here 85 and waits for an event to occur (like a key press or mouse event)." 86 GTK.Gtk main 87 ]
Figure 2.2, “Hello World Example Program” shows the window created by helloworld.st.
The classes and functions that are defined in the GTK
package are named as GTK.*. For example, the helloworld.st
program uses:
False GTK.Gtk mainquit GTK.GtkWindow GTK.GtkButton
from the GTK package.