Re: Application.Run()
- From: "Simon Tamman {Uchiha Jax}" <i_am_GETRIDOFTHISJUNKanti_everything@xxxxxxxxxxxxxxxxx>
- Date: Mon, 17 Oct 2005 12:04:36 GMT
That's excellent, thanks for the information!
I appreciate that you have trawled back through the posts to answer this
question that was left unanswered so long ago.
Many, many thanks.
UchihaJax (Simon)
"Richard Grimes" <richardg@xxxxxxxx> wrote in message
news:uG8hGoo0FHA.3660@xxxxxxxxxxxxxxxxxxxxxxx
> Uchiha Jax wrote:
> > What exactly is the "standard application message loop" (from MS
> > documentation:
> >
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemWindowsFormsApplicationClassRunTopic.asp)
> > and how does this differ to a standard thread event model?
> > Are there ways in which you can find out if an object requires the
> > "standard application message loop" other than trial and error?
> > Does anyone have any other information on this subject as I find it a
> > fascinating situation.
>
> new Form();
>
> just creates a form object, it does not create the form window
>
> Form f = new Form();
> f.Visible = true;
>
> the second line will create the window. In this property accessor a
> Win32 window class is registered, then a window is created. Every window
> has to have a windows procedure that handles messages. The messages are
> put into a queue for the thread and a loop on the thread calls
> GetMessage() to get a message from this queue and then passes it to the
> windows procedure by calling DispatchMessage().
>
> There is another aspect that you should be aware of. If a thread
> procedure returns, the thread dies. So if your application has just one
> thread, your application will live as long as the thread lives. (This
> assumes that the thread is a foreground thread.) Even if the application
> has a window and you have *not* clicked on the close button, if the
> thread procedure finishes then the application will die. Try this:
>
> class App
> {
> static void Main()
> {
> Form f = new Form();
> f.Visible = true;
> }
> }
>
> What happens? The form shows briefly and then goes away. The reason is
> that the window is created but the thread procedure completes so the
> process dies and the window is destroyed. Also, this window will not
> respond to windows messages. to get round this you can add a call to
> Application.Run() after the call to set the Visible property.
>
> Now the window will remain, because Run implements a
> GetMessage/DispatchMessage loop, so the main thread does not die. The
> loop also means that the form will handle messages sent by the OS.
> However there is a problem. If you click on the close button of the
> form, the window will go away, but if you run task manager you'll see
> that the process is still running. The problem is that the Visible set
> accessor provides a windows procedure that handles the click on the
> close button to close the window, but this windows procedure has no
> connection to the application - it cannot tell the application to end.
> This needs something called an application context, which is a
> connection between the window and the message queue. If you pass the
> form object to Application.Run an application context will be created. I
> won't go into the details, but basically the application context is
> based on the form, and if the form dies the application context breaks
> the message loop and so the process dies. If the message queue dies then
> the application context tells the form object (as opposed to the window)
> to allow your code to clean up (Dispose is called).
>
> Thus the life of the process is determined by the life of the form. Any
> other form in the application will not have the application context and
> so will not kill the process when it is closed.
>
> > I found I could "fix" my test by putting Application.Run at the end
> > of the thread that initializes the object. This is of course
> > equivalent to loading it into a Form and running the same thread in
> > the LoadEvent of the form. Having never encountered this problem
> > before I had some questions that I wondered if anyone could help me
> > understand.
>
> Hopefully the above will explain what's going on.
>
> I wrote an article for DDJ about this, but unfortunately you have to
> register to read it:
>
> http://www.ddj.com/documents/s=9698/ddj0505l/0505l.html
>
> I am considering writing a workshop on how windows forms work (on the
> lines of my workshops on Fusion and on Security), but to be honest at
> the moment I'm quite pissed off with Microsoft so I don't seem to have
> any incentive to do so.
>
> Richard
> --
> http://www.grimes.demon.co.uk/workshops/fusionWS.htm
> http://www.grimes.demon.co.uk/workshops/securityWS.htm
>
>
.
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