Can access a object after postback - ASP.NET

Question

I am really confused with this behavior. Can someone explain this to me?

I have the following class structure:

public abstract BaseUserControl : System.Web.UI.UserControl
{
  public List<string> listFieldMapper = new List<string>();
}

  public partial class Property : BaseUserControl
  {
    protected override void OnInit(EventArgs e)
    {
      base.OnInit(e);

      base.listFieldMapper.Add("test");
    }
  }

In a event handler of a button, (causes Postback), I can access the base.listFieldMapper

My understanding was that between postbacks, the state is not maintained, to be able to maintain the state, use the ViewState object. How is it that the list maintains the values?

On a side note, If I set the value of base.listFieldMapper after OnInit (Ex: Load), I have a null object after postback.

Answer 1

I would think that when a button click calls a postback:

1. When the server is handling the request, an instance of the user control is being instantiated.
2. The server then calls the method that handles the button click.

When the page is requested (not handling a button click):

1. When the server is handling the request, an instance of the user control is being instantiated.
2. The server then calls the method that handles the Load event.

Answer 2

The ViewState does not play a role in here. For it to track anything, you need to actually put something in it (most default properties do).

In your case, the sequence of events in the first case is (setting the list on init):

Control.OnInit -> add value
Page.OnInit    -> value present
Page.OnLoad    -> value present
Control.OnLoad -> value present
#PostBack
Control.OnInit -> add value
Page.OnInit    -> value present
Page.OnLoad    -> value present
Control.OnLoad -> value present
Button.OnClick -> value present

In the second case (setting the list on load):

Control.OnInit -> value absent
Page.OnInit    -> value absent
Page.OnLoad    -> value absent
Control.OnLoad -> add value
#PostBack
Control.OnInit -> value absent
Page.OnInit    -> value absent
Page.OnLoad    -> value absent
Control.OnLoad -> add value
Button.OnClick -> value present

And the listFieldMapper itself gets assigned in class constructor and will be non-null at any point in control's life cycle.

Answer 3

objLightBox