Hello Thai,
Even if we introduce these events, the adjustment of the splitter height will be "jumpy" -- i.e. the splitter height will not be adjusted until the animation finishes. It seems that you are trying to implement some way of auto-sizing the splitter, which is currently unsupported. You can use a setTimeout as a work-around, or disable the TreeView animation.
Greetings,
Alex Gyoshev
the Telerik team
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