How to Hide the DropDownList Behind Layer
A very common problem for modern web interface developers is displaying layers over a DropDownListBox. The DropDownListBox always wants to be displayed on top of any other control or layer in the page. This is because the DropDownListBox is actually a system control and not something controlled by the browser.
There is a common method to control this behavior that many are not aware of and it involves wrapping the DropDownListBox in a Div tag and using some JavaScript to control the display behavior.
Recently I came into a situation where I needed to display a layer as a Model dialog on top of my web page. The dialog layer would not hide a DropDownListBox that happened to be position directly behind it.
Hiding the DropDownListBox
Hiding the DropDownListBox involves wrapping it in a DIV or maybe a SPAN tag, depending on your preferences. In my case I also register a startup script because my Modal Dialog is displayed when the page is loaded, but you could just add this as a normal JavaScript method. In the JavaScript you need to set the visibility of the Div to hidden.
<
div id="'dlWrapperLayer'"> <asp:DropDownList ID="ddlMyList" runat="server"> </asp:DropDownList></div> Registering the Startup script is done in the code behind.
If Me.ClientScript.IsStartupScriptRegistered("ShowModalDialog") = False Then Dim sb As New StringBuilder sb.Append(
"document.all['ModalDialogLayer'].style.visibility = 'visible';document.all['PopUpBackGround'].style.height = 1500;document.all['PopUpBackGround'].style.width = window.screen.availWidth;document.all['PopUpBackGround'].style.visibility = 'visible';document.all['dlWrapperLayer'].style.visibility = 'hidden';") Me.ClientScript.RegisterStartupScript(GetType(printcopyfax), "ShowModalDialog", sb.ToString, True) End If I will try to remember to write an entry on doing a modal dialog soon, so don't worry.
Redisplay the DropDownListBox
I have a button on my dialog layer to close it, or essentially hide it from view. I leverage the onclick event handler to redisplay the drowdownlistbox.
<input id="cbDontShow" value="I Acknowledge" type="button" accesskey="S" title="Ackowledge Message." runat="server" onclick="document.all['ModalDialogLayer'].style.visibility = 'hidden';document.all['dlWrapperLayer'].style.visibility = 'visible';document.all['PopUpBackGround'].style.visibility = 'hidden';" /></td> Hopefully this will prove to be useful for you in the future.