How to be informed when gtk.paned slider’s position changed?

[Raymond <ranjiao gmail com>]

I wanna the hpaned to remember the slider position, then I need to catch 
the event of hpaned's changing slider position. According to official 
doc, paned only have a few signals, and none of them is about slider's 
position.

So, is there a event about hpaned's slider? And how to catch it?