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  • Workaround for ASP.NET 2.0 bug: LoadControl gives an exception in a TemplateControl

    Workaround for ASP.NET 2.0 bug: LoadControl gives an exception in a TemplateControl

    When you have your own custom TemplateControl and perform a LoadControl in there, this results in ax exception.


    For instance, the following code will trigger the exception:


    public class NavController : System.Web.UI.TemplateControl
    {
        public void LoadContent(string     url)
        {
                Control ctrl = this    .LoadControl(url);

                this    .Controls.Clear();
                this    .Controls.Add(ctrl);
        }
    }


    The exception you get is:


    [ArgumentNullException: Value cannot be null.
    Parameter name: basepath]
       System.Web.Util.UrlPath.Combine(String appPath, String basepath, String relative) +322
       System.Web.UI.TemplateControl.LoadControl(String virtualPath) +29
       SimpleContainer.NavController.LoadContent(String url)


    The reason for this is that the property AppRelativeTemplateSourceDirectory is not correctly initialized. The workaround for this is to add the following code to your TemplateControl:


    protected override void OnInit(EventArgs e)
    {
            this.AppRelativeTemplateSourceDirectory = Page.AppRelativeTemplateSourceDirectory;
            base.OnInit(e);
    }

    [Update: This bug no longer occurs in the RTM version]

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3 comments

  1. is this the correct vb port:

    Me.AppRelativeTemplateSourceDirectory = Page.AppRelativeTemplateSourceDirectory

    Me.OnInit(e)

    i just don’t know ehere to put it.

    Will

  2. This VB code should work AFAIK. You should put it in your own TemplateControl derived class, as an override of the OnInit function, as shown in the posting.

    In the postings sample, it would be the OnInit function of the NavController class.

    The VB syntax would be:

    Protected Overloads OnInit(EventArgs e)

    Begin

    Me.AppRelativeTemplateSourceDirectory = Page.AppRelativeTemplateSourceDirectory

    Me.OnInit(e)

    End

    Raimond

  3. Hi Raimond,

    I tried your workaround, but it doesn’t work. My class from where I call the LoadControl() method looks like this:

    namespace myNSbla

    {

    public class RenderContent : System.Web.UI.Page

    {

    private void NoRecord()

    {

    this.AppRelativeTemplateSourceDirectory = base.AppRelativeTemplateSourceDirectory;

    myobj tpl = (myobj)this.LoadControl("path");

    tpl.ArticleId = Guid.Empty;

    ContentPlaceholder.Controls.Add(tpl);

    }

    protected override void OnInit(EventArgs e)

    {

    this.AppRelativeTemplateSourceDirectory = Page.AppRelativeTemplateSourceDirectory;

    base.OnInit(e);

    }

    }

    }

    This class is located in a class library project, and is called from codebehind from a .aspx. I’ve tried all I know, but nothing works 🙁

    Greetings from Germany in hope of help 😉

    Thomas

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