Question

In my ASP.NET page, I have a generic class that is defined as below:

public partial class log_states : BasePage
{
    protected class StatesUsed
    {
        public int StateCode { get; set; }
        public string StateName { get; set; }
    }
    private List<StatesUsed> _statesUsed;
}

In the Page_Load() event, I initialize _statesUsed like below, and bind it to a grid:

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        _statesUsed = new List<StatesUsed>();
        BindMyGrid();
    }
}

private void BindMyGrid()
{
    gvStates.DataSource = _statesUsed;
    gvStates.DataBind();
}

I then have a form to add new States. When the user adds a state, I’m trying to add it to the local _statesUsed variable, and rebind the grid. Example:

protected void btnAddState_Click(object sender, EventArgs e)
{
    _statesUsed.Add(new StatesUsed { StateCode = 1, StateName = "Test" });

    BindMyGrid();
}

This always fails when trying to add the new item saying “Object reference not set to an instance of an object”…

How do I keep _statesUsed persistant? The idea is to add all user input using the generic class and then update the database at one go. If you know of another way to accomplish this, I’d be very grateful.

Thanks in advance!

Answer 1

Instead of

private List<StatesUsed> _statesUsed;

I’m usually using something similar to:

private List<StatesUsed> _statesUsed
{
    get
    {
        var result = ViewState["_stateUsed"] as List<StatesUsed>;

        if ( result == null )
        {
            result = new List<StatesUsed>();
            ViewState["_stateUsed"] = result;
        }

        return result;
    }
}

I.e. I am persisting page class variables to the ViewState.