[Hiki] create - Mechanism of signals and callbacks (ruby-gnome2-doc-cvs) - Ruby-GNOME2

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= Mechanism of signals and callbacks

Before looking at the "Hello World" program in details, we should study a bit how GTK handles signals and 
callbacks.

In the same way as your system delivers a signal to processes upon shutdown
((-Note that GTK signals are not related in any way with UNIX signals.  The GTK toolkit has been conceived 
to be independant of the underlying system. -)),  GTK sends a signal to the main loop (Gtk.main) when a 
special event occured.  The main loop will therefore call back the appropriate function of the widget.

Until a signal is received, the main loop will sleep.

In order to tell a GTK widget that it has to catch a specific signal, and then execute appropriate code,
we need to set a signal handler.

This can be done with the GLib::Instantiatable#signal_connect method, which is part of the Ruby/GLib library 
(do not forget that GTK is built on GLib):

  GLib::Instantiatable#signal_connect("signal name") do
      # Code to execute when "signal name" will been catched.
  end

GLib::Instantiatable#signal_connect needs 2 things:
* the name of the signal which will be catched; 
* a block code that will be executed upon reception of the given signal.

The block code can take an optional parameter as follows:

  GLib::Instantiatable#signal_connect("signal name") do |w|
      # ...
  end

The widget which issues the signal will be therefore substituted by the parameter w.

Ruby-GNOME2

[ruby-gnome2-doc-cvs] [Hiki] create - Mechanism of signals and callbacks