CODEWITHSUNDEEP
c#asp.net
kyletme
kyletme

Reputation: 471

Collection was modified; enumeration operation may not execute

I keep getting the following warning (not error) in a production ASP.Net application:

System.Web.HttpUnhandledException: Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
at System.Web.UI.ControlCollection.ControlCollectionEnumerator.MoveNext()
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
at System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer)
at System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output)
at System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
at DMAC.UI.Master.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
at System.Web.UI.Page.Render(HtmlTextWriter writer)
at Telerik.Web.UI.RadAjaxControl.RenderPageInAjaxMode(HtmlTextWriter writer, Control page)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
at System.Web.UI.Page.Render(HtmlTextWriter writer)
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
--- End of inner exception stack trace ---
at System.Web.UI.Page.HandleError(Exception e)
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.UI.Page.ProcessRequest()
at System.Web.UI.Page.ProcessRequest(HttpContext context)
at ASP.scan_history_aspx.ProcessRequest(HttpContext context)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Here is the code for the Render method where the error is occurring:

protected override void Render(HtmlTextWriter writer)
    {
        Header header = new Header();
        List<Menu> menus = DMAC.Application.Current().Menus;
        Menu menu = menus.Find(m => m.MenuId == MenuId);

        SiteMapWindow siteWindow = new SiteMapWindow();
        siteWindow.OpenerId = Menu.PATHID;
        this.Page.Form.Controls.Add(siteWindow);

        SupportWindow supportWindow = new SupportWindow();
        supportWindow.OpenerId = Menu.SUPPORTID;
        this.Page.Form.Controls.Add(supportWindow);

        this.Page.Form.Controls.AddAt(0, menu);
        this.Page.Form.Controls.AddAt(0, header);

        Scripts.GoogleAnalytics.RegisterScript(this.Page);
        base.Render(writer);
    }

I cannot recreate the error myself. Any ideas?

Upvotes: 1

Views: 2040

Answers (1)

user166390
user166390

Reputation:

I would suspect the problem arises from adding (non-child) controls in Render

That is, the controls are added to the Page Control Collection which is likely being iterated over in order to Render children. (And I am presuming that includes this code; in a child control.)

Move the layout modifications (really, everything in the method) into CreateChildControls or what may be appropriate. (I'm not sure CreateChildControls is actually okay here -- the issue, I believe, is the Page Controls aren't children.)

Happy coding.

Upvotes: 0

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