Why does Application_BeginRequest() fire twice when refreshing browser?

Question

I'm observing some really confusing behavior with the Application_BeginRequest event in my Global.asax file (in an ASP.NET MVC app). When running through the debugger, if I Refresh my browser (IE7), this event fires twice. If I click a link or otherwise manually request a page, it fires once - as expected.

Why does a refresh cause BeginRequest to fire twice?

I'm observing this with a brand new MVC project with the following addeded to Global.asax.cs

protected void Application_BeginRequest() { 
    //executed twice
}

For context, I'm trying to add a new object to the HttpContext.Current.Items collection during this event, so it will persist through the entire request process. Obviously, I don't want this to happen twice for a single refreshed request!

Answer 1

Are you sure it's really 2 request to the same URL? I would think that the second is probably some dynamic JS, CSS or image file. Try to find out either with Fiddler or by looking at HttpContext.Current.Request.Uri in the debugger

Answer 2

Something that surprised me a while back was that if you have an img tag in your html that doesn't have a proper image path, some browsers will make a request to the original page. Here is a related blog post.