In PyQt4 programming, I can re-implement widget's resizeEvent method to handle resize events. But I this method doesn't work for plasmoid. So how to handle resize event in plasmoid? Thanks in advance.

Please check that you are using the correct function signature: http://api.kde.org/4.x-api/kdelibs-apid ... 1242731371

Alternately, it may not be supported:
http://api.kde.org/4.x-api/kdelibs-apid ... cript.html

Thanks really. But it seems that the plasmoids could only handle resize event in constraintsEvent method. See:
http://api.kde.org/4.x-api/kdelibs-apid ... 1560cda651

When resizing, constraintsEvent is called but resizeEvent is not, even with right signature.

It appears that you have either:
A) Come across a lacking in the scripting API
B) A bug.

Please ask on the Plasma mailing list ( plasma-devel@kde.org ) for more information.