Re: Events and signals

[Jeff Franks <jcf tpg com au>]

Fabio Zanetta wrote:

> Hi,
>
> Here another distinguish-question :)
>
> What is the difference between events and signals?

Events correspond to the events in the X event mechanism and are 
declared in gdkevents.h. They are more low level. Signals are defined by 
 widgets and are used to signal that something has happend to the 
widget. At which point a widget will pass control to any connected 
callback functions. For convenience, GtkWidget wraps the GDK (X) events 
in a signal. These signals are suffixed with "_event". You can connect 
to events and signals in the same way, with g_signal_connect(). Events 
pass an event struct to connected callack functions that often contains 
extra information, like x and y cursor cordinates in GdkButtonEvent.

> Why I sould use g_signal_connect() instead of gtk_widget_set_events()?

You must use g_signal_connect() to connect to events and signals. You 
would use gtk_widget_set_events() when you want to set the events a 
widget will receive. Most widgets have a default set of events they 
receive. If you want to receive extra events you would call 
gtk_widget_set_events() if the widget has not been realized, and 
gtk_widget_add_events() if it has. Be careful though, you might change 
the way a widget behaves, for better or worse.

> And how can I trap a event? (with signals I can use a callback function...
> but with events?)
You can use callback functions, in the same way, just use the right 
callback function signature.

> And also... for a Button I can only find out the "clicked" signal... there
> are others? Where can I find docs on it?

Look in the reference docs in your source directory, docs directory or 
online and you will find "gtk/gtkbutton.html" and "gdk/gdk-events.html". 
gtkbutton.html lists the button signals and what they mean. 
gdk-events.html lists all the events and what they mean.

> Can I know if a widget can accept or not the "xyz" signal?

A widget inherits the signals of the widget it derives from. So look at 
the reference docs for the widget you're interested in. The signals are 
listed at the bottom of the page. Then look at the its parent, and its 
parent, and so on. Although a widget inherits a signal from its parent, 
its default response to the signal might be different.


Jeff Franks.