Conditional Validation in DataGrids

I have an insert row in the footer of a DataGrid. I need to validate user data on each text box but only when the "Add Button" is clicked, otherwise empty textboxes will flag a warning preventing the user even from moving between pages.

I thought of using a custom validator and checking that the add button was clicked to submit the form, but I'm not sure as to the syntax to follow. Has anyone done any of this before??

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