Could someone explain this interesting ASP.NET HTTP pipeline events behavior?

Question

It is clear that member variables of an ASP.NET page should lose scope every time the page is refreshed.

I have the following code to display a grid of "Alerts" with edit capabilities:

public partial class Alerts : System.Web.UI.Page
{
    private _WikiSyntaxEngine;

    protected void Page_Load(object sender, EventArgs e)
    {
        _WikiSyntaxEngine = new WikiSyntaxEngine();
    }

    protected void gvAlerts_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        var alert = (DataModel.Alert)(e.Row.DataItem);
        // Below is the only line of interest, because only when published
        // to the server would it throw an exception...
        string html = _WikiSyntaxEngine.ConvertWikiTextToHTML(alert.Description);
    }
}

It was only on the development server to which I published did this code fail (i.e. throws a NullReferenceException because _WikiSyntaxEngine was null) during an update to the row.

However, on my local machine the code runs just fine - the row is updated and the grid refreshes as expected.

I have since fixed the code to make the WikiSyntaxEngine a singleton, or the way it should have been designed from the beginning because it shouldn't have to be instantiated everywhere it is used.

My question then, is how can the Page_Load event be called before gvAlerts_Databound() on my local machine (as expected), but not called on the development machine resulting in the NullReferenceException for _WikiSyntaxEngine?

Answer 1

I'm assuming that your gvAlerts GridView is defined in the ASP.NET markup of the page. If this is the case, it is probably being DataBound in the OnInit() event, not on Page_Load(), where you're instantiating WikiSyntaxEngine.

You probably should use OnInit() to instantiate your WikiSyntaxEngine if your GridView is getting bound before Page_Load.

As for why you're getting different behavior in development and production is still a mystery to me.