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70 lines
2.5 KiB
Plaintext
70 lines
2.5 KiB
Plaintext
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Things to care about when using/programing for GTK+
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===================================================
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This file is meant to collect some frequently triggered failures when
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programming for/with Gtk, having the spirit of a developers FAQ.
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It is also the correct place to list up things that programmers should
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care about in general.
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In the hope that this text might be usefull to someone,
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- Tim Janik <timj@gimp.org>
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1998/02/11
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Automatic destruction of widgets on removal from parent
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-------------------------------------------------------
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This is a reference counting issue, you would want to refer
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to refcounting.txt on it.
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What are all the widget flags about?
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------------------------------------
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Refer to the file widget_system.txt which covers widget flags and the
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resulting invariants in a detailed way.
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GdkWindow pointers may be NULL in GdkEvents
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-------------------------------------------
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The notification nature of the signal mechanism might cause events to
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be emitted that have their GdkWindow pointer set to NULL.
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This is due to the fact that certain events need to be emitted after the
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real GdkWindow of a widget is not any longer pertinent.
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It's up to the signal handling function (application) to check for the
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window field of the event structure to be != NULL, if it is going to
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perform any operations through Gdk calls on it.
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Events that a likely to trigger a missing check for the window pointer
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currently are (and correspond to the trailing signals):
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GDK_SELECTION_CLEAR GtkWidget::selection_clear_event
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GDK_FOCUS_CHANGE GtkWidget::focus_in_event
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GtkWidget::focus_out_event
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Events that are asured to have a valid GdkEvent.any.window field are
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GDK_EXPOSE GtkWidget::expose_event
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gtk_widget_ref() vs. gtk_object_ref()
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-------------------------------------
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The widget referencing functions gtk_widget_ref() and gtk_widget_unref()
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are currently just wrappers about the corresponding referencing functions
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for objects. Still you should use the widget referencing functions if you
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are sure the referenced object is of type GTK_WIDGET_TYPE.
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Writing Gdk functions
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---------------------
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When writing Gdk functions that operate on GdkWindow structures in any
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maeningfull sense, that is casting to a GdkWindowPrivate structure for
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access to fields other then GdkWindow.user_data, the programmer is
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recommended to check for the GdkWindowPrivate.destroyed field to be ==
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FALSE, especially if the GdkWindowPrivate.xwindow field is used.
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Silent abortion of the Gdk function is the correct behaviour if this
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condition isn't met.
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