What do you do when you can't use ViewState?

Question

I have a rather complex page that dynamically builds user controls inside of a repeater. This repeater must be bound during the Init page event before ViewState is initialized or the dynamically created user controls will not retain their state.

This creates an interesting Catch-22 because the object I bind the repeater to needs to be created on initial page load, and then persisted in memory until the user opts to leave or save.

Because I cannot use ViewState to store this object, yet have it available during Init, I have been forced to store it in Session.

This also has issues, because I have to explicitly null the session value during non postbacks in order to emulate how ViewState works.

There has to be a better way to state management in this scenario. Any ideas?

Edit: Some good suggestions about using LoadViewState, but I'm still having issues with state not being restored when I do that.

Here is somewhat if the page structure

Page --> UserControl --> Repeater --> N amount of UserControls Dynamicly Created.

I put the overridden LoadViewState in the parent UserControl, as it is designed to be completely encapsulated and independent of the page it is on. I am wondering if that is where the problem is.

Answer 1

The LoadViewState method on the page is definitely the answer. Here's the general idea:

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

  // Get repeaterData from view state before the normal view state restoration occurs.
  repeaterData = savedStateArray[ 0 ];

  // Bind your repeater control to repeaterData here.

  // Instruct ASP.NET to perform the normal restoration of view state.
  // This will restore state to your dynamically created controls.
  base.LoadViewState( savedStateArray[ 1 ] );
}

SaveViewState needs to create the savedState array that we are using above:

protected override object SaveViewState() {
  var stateToSave = new List<object> { repeaterData, base.SaveViewState() };
  return stateToSave.ToArray();
}

Don't forget to also bind the repeater in Init or Load using code like this:

if( !IsPostBack ) {
  // Bind your repeater here.
}

Answer 2

This also has issues, because I have to explicitly null the session value during non postbacks in order to emulate how ViewState works.

Why do you have to explicitly null out the value (aside from memory management, etc)? Is it not an option to check Page.IsPostback, and either do something with the Session variable or not?

Answer 3

I have always recreated my dynamic controls in the LoadViewState event. You can store the number of controls needed to be created in the viewstate and then dynamically create that many of them using the LoadControl method inside the LoadViewState event. In this event you have access to the ViewState but it has not been restored to the controls on the page yet.