Ajax Enabled .NET Server Control registered

Question

I've created an Ajax enabled .NET Server control. This control inherits a Panel and implements the IScriptControl (in order to enable the Ajax component of the control).

It's pretty simple actually. It's essentially a Panel that has a style of overflow:scroll (it's a "scrollable Panel") and it remembers it's scroll position between asynchronous postbacks to the server so that the scroll position is not reset to 0,0 when the asynchronous postback returns.

Everything's been working for some time now (years) but I never tried to make this control invisible (server side). Even if I set the parent of this control to Visible=false this control is not working properly.

I'm getting an exception thrown by the Ajax.NET framework in the web browser:

Error: Sys.ScriptLoadFailedException: The script "http://UrlToAScript" contains multiple calls to Sys.Application.notifyScriptLoaded(). Only one is allowed.

It has something to do with the Render event not being fired (because the control is not visible, it's not rendered so the Render event doesn't actually take place). When the control is made visible (and the Render event does take place) I'm seeing the exception in the web browser (client side) stating that it's registered more than once. (Hopefully I'm speaking to an audience that understands that the ScriptDescriptors are registered with the ScriptManager in the Render event of Ajax enabled server controls.)

Here is my implementation that handles the OnPreRender and Render events:

Protected Overrides Sub OnPreRender(ByVal e As System.EventArgs)
        Me.Style.Add("overflow", "scroll")

        If Not Me.DesignMode Then
            If ScriptManager Is Nothing Then
                Throw New HttpException("A ScriptManager control must exist on the page.")
            End If
            ScriptManager.RegisterScriptControl(Me)
        End If
        MyBase.OnPreRender(e)
    End Sub
    Protected Overrides Sub Render(ByVal writer As System.Web.UI.HtmlTextWriter)
        'Register the ScrollContiner's script descriptors that are created by the GetScriptDescriptors method
        If Not Me.DesignMode Then
            ScriptManager.RegisterScriptDescriptors(Me)
        End If
        MyBase.Render(writer)
    End Sub
    Public Function GetScriptReferences() As System.Collections.Generic.IEnumerable(Of System.Web.UI.ScriptReference) Implements System.Web.UI.IScriptControl.GetScriptReferences

        Dim reference As ScriptReference = New ScriptReference()
        reference.Name = "MyNamespace.ScrollContainer.js"
        reference.Assembly = "MyNamespace"

        Return New ScriptReference() {reference}
    End Function 
    Public Function GetScriptDescriptors() As System.Collections.Generic.IEnumerable(Of System.Web.UI.ScriptDescriptor) Implements System.Web.UI.IScriptControl.GetScriptDescriptors
        Dim descriptor As ScriptControlDescriptor = New ScriptControlDescriptor("MyNamespace.ScrollContainer", Me.ClientID)
        descriptor.AddProperty("LeftScrollPosition", Me.LeftScrollPosition)
        descriptor.AddProperty("RightScrollPosition", Me.RightScrollPosition)
        descriptor.AddProperty("ScrollPositionMessengerName", Me.ScrollPositionMessengerName)
        Return New ScriptDescriptor() {descriptor}
    End Function

I have no idea how to get around this problem. Any insight would be greatly appreciated.

Thanks a lot,

-Frinny

Answer 1

I found the answer to my problem.

I had the following in my JavaScript code that my Ajax enabled server control used:

if (typeof (Sys) !== 'undefined')  Sys.Application.notifyScriptLoaded();

For some reason this line is also (automatically) added by .NET if the control's visibility state changes on the server. The strange thing about it is that .NET only added it when the control's visibility state changed and not every time.

I removed my "if (typeof (Sys) !== 'undefined') Sys.Application.notifyScriptLoaded();" and just let .NET add this line for me and everything works fine now.

Edit: apparently this line is automatically added to the Control's JavaScript when you use the ControlJS template. So, beware of this problem if you're creating controls. Make sure you remove this line or you'll probably experience the same issue as I did.

Thanks for your time!

-Frinny

Answer 2

I removed this as well if (typeof(Sys) !== 'undefined') Sys.Application.notifyScriptLoaded(); but it did not solve problem for the Timeout control. The ScriptManager is defined on the Master page and the control is defined on the master page.

Answer 3

I ran into this strange problem today, and you saved me. Thanks

Answer 4

Thank you my Work fine untill i add it to a list View Then I got this error