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Asked: 2026-05-13T23:35:04+00:00

My original understanding was that the asp.net page lifecycle is run once for all

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My original understanding was that the asp.net page lifecycle is run once for all pages and controls under normal circumstances. When I attached a control during a container’s OnPreRender, I encountered a situation where the control’s OnInit was not called. OK, I considered that a bug in my code and fixed as such, by attaching the control earlier.

But just today, I encountered a situation where OnInit for a control seems to be called after the normal OnInit has been done for everyone else. See stack below. It seems that during the page’s PreRender, the control’s OnInit is called as it is being dynamically added.

So I just want to confirm exactly what ASP.NET’s behavior is? Does it actually keep track of the stage of each control’s lifecycle, and upon adding a new control, it will run from the very beginning?

[HttpException (0x80004005): The control collection cannot be modified during DataBind, Init, Load, PreRender or Unload phases.]
System.Web.UI.ControlCollection.Add(Control child) +8678663
MyCompany.Web.Controls.SetStartPageWrapper.Initialize()
MyCompany.Web.Controls.SetStartPageWrapper.OnInit(EventArgs e)
System.Web.UI.Control.InitRecursive(Control namingContainer) +333
System.Web.UI.Control.InitRecursive(Control namingContainer) +210
System.Web.UI.Control.AddedControl(Control control, Int32 index) +198
System.Web.UI.ControlCollection.Add(Control child) +80
MyCompany.Web.Controls.PageHeader.OnPreRender(EventArgs e) in
System.Web.UI.Control.PreRenderRecursiveInternal() +80
System.Web.UI.Control.PreRenderRecursiveInternal() +171
System.Web.UI.Control.PreRenderRecursiveInternal() +171
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +842

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1 Answer

  1. Editorial Team

    A control’s OnInit is called as soon as it’s added to the control tree. In your stack you can see this happening, this occurs:

    System.Web.UI.Control.AddedControl(Control control, Int32 index) +198   
System.Web.UI.ControlCollection.Add(Control child) +80

    Then this is triggered:

    MyCompany.Web.Controls.SetStartPageWrapper.OnInit(EventArgs e)

    So at whatever point in the lifecycle it’s added, it’s OnInit kicks off.

    Egghead has a good image depicting normal event lifecycles between pages and controls, but just keep in mind that something can’t be executing events if it doesn’t exist yet…if it’s just added, it has to catch up on events at that point instead of when they would have happened if the controls were in markup or CreateChildControls.

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