Since there is no easy way for preserving the changes for rows with failed validation after postback, what I could suggest is that you handle the row validation entirely on client-side and allow the user to save only when the validation for all rows passes.
For your convenience I am attaching a simple example demonstrating such client-side validation, where you could go through each row, get reference to any of the cells of that row and validate each value. This should be achieved in the client-side OnCommand
event of the grid. If the validation fails for any row you could cancel the command, which will prevent the postback.
Please give a try to the attached sample page and see if the same approach could be used for your requirement.
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