PolicyList.aspx
<asp:TextBox ID="txtFirstName" runat="server" Font-Size="14px" ></asp:TextBox>
WebForm1.aspx
<asp:TextBox Width="100%" ID="txtNameOfInsured" runat="server">
<asp:Button ID="btnPolicy" runat="server" Text="Policy" />
<cc1:ModalPopupExtender ID="mp1" runat="server" PopupControlID="Panl1"
TargetControlID="btnPolicy" CancelControlID="btnCancel" BackgroundCssClass="Background" PopupDragHandleControlID="Panl1">
</cc1:ModalPopupExtender>
<asp:Panel ID="Panl1" runat="server" CssClass="Popup" align="center" style = "display:none">
<iframe style=" width: 350px; height: 300px;" id="irm1" src="PolicyList.aspx" runat="server"></iframe>
<br/>
<asp:Button ID="btnOK" UseSubmitBehavior="false" OnClick="OkButton_Clicked" runat="server" Text="OK"></asp:Button>
<asp:Button ID="btnCancel" runat="server" Text="Close"></asp:Button>
</asp:Panel>
and codebehind
protected void OkButton_Clicked(object sender, EventArgs e)
{
TextBox textbox1 = (TextBox)Panl1.FindControl("txtFirstName");
txtNameOfInsured.Text = textbox1.Text;
}
But doesn't work textbox1 is null, Could you help me? thanks