Question

I have a user control where i registered idle event under Load event of that control.

Control_Load(object sender, System.EventArgs e)
{
    Application.Idle += new EventHandler(Application_Idle);
}

I know this will trigger when application finishes processing and reached idle state.But i really confused what is application here which goes idle, does that this usercontrol where load event register the idle event handler.When i put breakpoint every time it hits, what does this means?

For example i created a Form which contains this code

int counter = 0;
private void Form1_Idle(object sender, System.EventArgs e)
{
    counter++;
    label1.Text = counter.ToString();
}

private void Form1_Load(object sender, System.EventArgs e)
{
    Application.Idle +=new EventHandler(Form1_Idle);
}

then i create some buttens in that form which has certain operations to do.As per my understading label counter should not increase when i am doing operations through the buttons i created because its not in idle state, but now what happens is even some operation going on by clicking button lable counter is increasing, except if i press form title bar and move the form around.

One more thing do i need to detach these event handler when close my window even if this is main application window. If so if i do in dispose method will that sufficient?

protected override void Dispose(bool disposing)

UPDATE
if i am pressing some text through keyboard say “LARSEN” ,between the press of alphabet “L” and “A” does idle event occurs?

Answer 1

It triggers every time when it have processed all the messages and there are no messages left. As for disposing, per MSDN “Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.” – so I guess detaching it on form dispose (or probably on form close if its handler has something to do with the form) is enough.

upd: message loop is started in your Program.cs like this:

    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new frmMain());
    }

It processes all the messages like mouse move, key pressed and lots and lots more. You probably should read in length about it somewhere, possibly a book, but yes, there is an “idle” state after your first keypress is processed, long before you hit second key.

upd2: If you want to detect “real idle” you might want to start (and re-start) some sort of timer in this handler and when it expires maybe check CPU load or some such, depending on exact desired condition.