How to hide gridview

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I am using a required validation control to force the user to select a value from the drop downs.If they are not selected the valiation summary will display a reminder for the user to select a values and once they do the data will be display in the gridview controls.if they want to go back and change the value and did not select the value then I would like to hide the previous gridview result and show them on the validation summary that they need to select a value.How can I hide the gridview in this kind of sceneria. thanks for the help. I try the below code but did not give me the result I wanted

If valSummary.Visible = True Then
gvFedBrdg.Visible = False
Else
gvFedBrdg.Visible = True
End If