I need to call Rowdatabond after post back
RowDataBound is called when you bind rows to grid. If for some reason (which you already specified!) you want to call the event then you need to rebind the grid.
Details here:
MSDN: GridView.RowDataBound Event[
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BTW, I am not sure how are you going to resolve your issue by calling it again. One of the extra step: you will have to re-store the checkboxes state once you have re-binded.