HttpContext in eventhandler

First off all, i would like to thank Adil Baig to show Developers (specifically in MOSS) like us that thing like this can be done in first place.

I often heard that HttpContext is null in event handler and we cannot use session and Request.QueryString.
Here is the solution.

public class MyEventHandler: SPItemEventReceiver
{
HttpContext current;
public MyEventHandler()
{
current = HttpContext.Current;
}

public override void ItemAdding(SPItemEventProperties properties)
{
/// some thing went wrong so you need to cancel the event and redirect
}

With this Context you can find all the properties you want.
In SharePoint there is not any functionality for displaying our customized error page.
Like if for data validation in event/item handler we use

properties.ErrorMessage = “Opps... Not allowed”;
properties.Cancel = true;

And validation message displayed in SharePoint error Page which looks error in application.
But with this Context you can use to redirect to any of your custom or any out of the box Page.

SPUtility.Redirect(Url, SPRedirectFlags.Default, current);

HttpContext is available only in synchronous event like ItemAdding and ItemUpdating.

More Info Click Here