Calling a confirm dialog box on code behind and get the chosen option

Question

I'm developing an asp.net application and I need to call a confirm dialog box on the code behind. And after that, I need to get the user's click (if he clicked at OK or Cancel).

If he clicked the OK button of the dialog, I must continue to running the code where I stopped before call the dialog.

To solve this problem I thought in put at the aspx an input of type button, and set it's style to visibility:hide. So, when the users click on the OK button the programm will call this hidden button which calls a method that will continue the job stopped.

I'll post my code, I expect it might help.

The code below is on my code behind, and it calls the confirm dialog.

System.Web.UI.
    ScriptManager.RegisterClientScriptBlock(this, GetType(), "__Mensagem", "if (confirm('" + CustomMessage + "')){document.getElementById(\'<%=btnSave.ClientID%>\').click();}", true); 

The code below is on my aspx, it's the "hidden" button.

<input style="visibility:hidden;" id="btnSave" runat="server" onclick="btnSave_Click"/>

I don't know why isn't working. The error that I receive after click on the button OK of the confirm dialog box is the following: Erro em tempo de execução do Microsoft JScript: 'document.getElementByID(...)' é nulo ou não é um objeto

I'm from Brazil so the error is in portuguese, a translation to english it's something like this:

"A runtime error occurred on Microsoft JScript 'document.getElementByID(...)' is null or is not an object"

I give a look at the html code of the page and I notice that the button isn't there.

Maybe it's because I'm using an UpdatePanel, but when I removed it (just for tests, I must use the Update Panel), the same error is showed, and in this time the button were on the page's html code.

Answer 1

A stab in the dark.

In your code-behind have you set btnSave.visible = false;? If so, this would prevent the button from being rendered to the HTML.

Also, is there any reason you're not using the ASP:Button control, rather than a mix of HTML with runat="server"?

Finally, it may help to have type='button' on your <input....

UPDATE

The problem is you're trying to apply an inline tag document.getElementById(\'<%=btnSave.ClientID%>\')

in your code be <%=btnSave.ClientID%> does not exist yet.

your code will break the moment you put your button inside another server control, as the clientId will become different.

Change the code to this:

     document.getElementById('" + btnSave.ClientID + "')

and it will work, regardless of where you have the button.