Injecting javascript from a user control inside an UpdatePanel

Question

When the page initially renders, the initializeControl function is called and everything works.

When the page performs a full post-back (via a submit button), the initializeControl function is also called and everything works.

When there is partial post-back of the UpdatePanel, though, the initializeControl function is never called and the control stops working.

HTML:

<asp:ScriptManager ID="myScriptManager" runat="server" />
<asp:UpdatePanel ID="myUpdatePanel" runat="server">
    <ContentTemplate>
        <uc:MyControl ID="myControl" runat="server" />
    </ContentTemplate>
</asp:UpdatePanel>

User Control:

Protected Overrides Sub Render(ByVal writer As HtmlTextWriter)
    Dim initializeScript = String.Format("initializeControl('{0}');", ClientID)

    Page.ClientScript.RegisterStartupScript(GetType(Page),
        New Guid().ToString(), initializeScript, True)

    MyBase.Render(writer)
End Sub

For testing purposes, assume the initializeControl function is just a debugger; (the content of the function works fine - it's just not being called when it needs to be).

Please keep in mind that there is no way (that I know of) for the user control to know if it is inside an UpdatePanel or not, and there is also no way it can access the ScriptManager element on the parent page in server code.

Thanks in advance.

P.S. I know UpdatePanels are awful and should be avoided at all costs, but I am working with hundreds of consuming pages that are already using them and they can not be changed.

Community · Accepted Answer · 2017-05-23 12:27:56Z

2

It's most likely due to the fact that the page update is happening through the update panel. Startup scripts can have issues with not firing in these cases, and need to be wrapped in:

Sys.Application.add_load(function(){ myFunctionCall(); });

It's the Microsoft AJAX library's way of ensuring your startup script happens when it should during MS AJAX roundtrips.

Here's an easy way to ensure all client scripts added to the page work, regardless of whether they are contained in an ajax updatepanel or not. We use this in all of our projects and it works flawlessly:

ASP.Net - Javascript inside AJAX UpdatePanel

edited May 23, 2017 at 12:27

CommunityBot

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answered Oct 16, 2012 at 15:22

KP.

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3 Comments

jbabey Over a year ago

i snagged the function from your other answer - upon partial postback of the update panel it appears to be calling the initializeControl function twice - any thoughts?

jbabey Over a year ago

I removed the scriptText = String.Concat("Sys.Application.add_load(function(){", scriptText, "});") from the function and it appears to be working well, thanks!

KP. Over a year ago

@jbabey good stuff. Yes my answer here is if you were simply going to use it in isolation. The linked question/answer is a complete solution that doesn't require you to add the add_load call because the code does it for you.

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