How to validate the form when positive button click?

I have my dialog with some form. when user click positive button if form has errors they should be shown and dialog shouldn't dismiss. if all are validated then it should be closed. when neagative button clicked, dialog should dismiss. how can i achieve this?

No source files, tests, or entry points are identified in the issue. Start by inspecting the dialog's positive and negative button API and any usage examples, then verify whether form errors can prevent dismissal while a valid form closes and the negative action always dismisses.

Written by the indexing model from the issue text.