I'm wondering if you can disable the RequiredFieldValidator when a certain button is clicked and be enabled when another button is clicked?

I tried with enable = false and true but it didn't work because the onclick event isn't triggered before the right value has been writen.

public void btnNext_OnClick( object sender, System.EventArgs e )
{
rfvZipCode.Enabled = true;
Response.Redirect( "B.aspx" );
}
public void btnPrev_OnClick( object sender, System.EventArgs e )
{

rfvZipCode.Enabled = false;
Response.Redirect( "C.aspx" );
}

<asp:RequiredFieldValidator ID="rfvZipCode" ErrorMessage="Du mste fylla i ett postnr" Runat="server" ControlToValidate="tbZipCode" />