R – Catching events from dynamically added ASP.NET User Controls

This is based on .NET v1 event sequence, but it should give you the idea:

• Initialize (Init event)
• Begin Tracking View State (checks if postback)
  • Load View State (if postback)
  • Load Postback Data (if postback)
• Load (Load event)
  • Raise Changed Events (if postback)
  • Raise Postback Events (if postback)
• PreRender (PreRender event)
• Save View State
• Render
• Unload (Unload event)
• Dispose

As you can see, the loading of ViewState data back to the controls happen before the Load event. So in order for your dynamically-added controls to "retain" those values, they have to be present for the ASP.NET page to reload the values in the first place. You would have to re-create those controls at the Init stage, before Load View State occurs.

I agree with the other points made here "If you can get out of creating controls dynamically, then do so..." (by @Jesper Blad Jenson aka) but here is a trick I worked out with dynamically created controls in the past.

The problem becomes chicken and the egg. You need your ViewState to create the control tree and you need your control tree created to get at your ViewState. Well, that's almost correct. There is a way to get at your ViewState values just before the rest of the tree is populated. That is by overriding LoadViewState(...) and SaveViewState(...).

In SaveViewState store the control you wish to create:

protected override object SaveViewState()
{
    object[] myState = new object[2];
    myState[0] = base.SaveViewState();
    myState[1] = controlPickerDropDown.SelectedValue;

    return myState
}

When the framework calls your "LoadViewState" override you'll get back the exact object you returned from "SaveViewState":

protected override void LoadViewState(object savedState) 
{
    object[] myState = (object[])savedState;

    // Here is the trick, use the value you saved here to create your control tree.
    CreateControlBasedOnDropDownValue(myState[1]);

    // Call the base method to ensure everything works correctly.
    base.LoadViewState(myState[0]);
}

I've used this successfully to create ASP.Net pages where a DataSet was serialised to the ViewState to store changes to an entire grid of data allowing the user to make multiple edits with PostBacks and finally commit all their changes in a single "Save" operation.