a queseion about gtk_emit_signal_by_name

[tigerlei <lzy os pku edu cn>]

Hi
I am developing a GTK+ program.
I want to send a signal to a GtkDrawingarea to call it re-draw its contents
and I used such code:
/********************/
gtk_signal_emit_by_name(drawingarea1,"expose_event");
and aslo try like this:
/********************/
gtk_signal_emit_by_name(drawingarea1,"eevent");

but the program excute and exit with error as :
/******************************/
GLib-GObject-WARNING **: gsignal.c:2214: value location for `gboolean'
passed as NULL
Segmentation fault
/******************************/

so , I try again:
/*********************/
gboolean ret;
gtk_signal_emit_by_name(drawingarea1,"expose_event",&ret);

this time , the error is:
/******************************/
Segmentation fault
/******************************/

what is the problem of this case?
I am a newer of GTK+
please help me :)

many thanks! 
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