Hi Wirat Chinnan,
Unfortunately current version of RadGridView control doesn't support such scenario. You could override TAB key behavior, like in the attached example (take a look at CustomKeyboardProvider class and its usage). This code will give you control over TAB key behavior.
P.S. We have plans to improve TAB navigation in such scenarios, but I cannot commit with any specific date or release.
All the best,
the Telerik team
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