How to redraw the drawing area when the drawing area resized?

["xiaofeng xu" <kelvenxu gmail com>]

I have a vertical paned with a drawingarea and textview in it. When I move the bar of vertical paned, the size of drawingarea is changed, and the picture in the drawing area disappear.
I want to know: How can I redraw the drawing area when the  drawing area resized? I haved handle the event expose-event. I tried to handle size-allocation event, but it doesn't work. Can someone help me or give me a example, thank you!