ASP.net control Postback Problem (Can't read the value the user entered!)

Question

I've written a custom widget to allow a user to select a location from a database of locations. This is my first ASP.net custom control. It seemed like everything was working fine, but now there's a problem.

My control implements the RaisePostBackEvent function as follows:

public void RaisePostBackEvent(string eventArgument)
{
    SelectedLocationId = eventArgument.Split('|')[0];
    SelectedLocationDescription = eventArgument.Split('|')[1];
}

I wrote a test page and included the following in my ASP code:

<%= locationSelector.SelectedLocationId %>

That worked fine.

However, in my web application, the following code does not work:

    protected void Page_Load(object sender, EventArgs e)
    {
        if (Page.IsPostBack)
         Response.Write(locationSelector.SelectedLocationId);
         // SelectedLocationId is null here!!!
    }

When I run this code in the debugger, I see that my Page Load event fires before the Post Back event! Therefore, the data is not yet read from the postback. I know that using the MS provided text field control, the text is available at Page Load, so I think I must be doing something wrong.

How can I read the location that the user selected when the Page Load event fires? To clarify, I'm refering to the Page Load of a web application page.

Answer 1

You're setting SelectedLocationId on a postback event and at the same time you are trying to retrieve its value on the first load. SelectedLocationId will be null all right.

Try:

protected void Page_Load(object sender, EventArgs e)
    {
       if (locationSelector != null)
         Response.Write(locationSelector.SelectedLocationId);
    }