How to detect when the mouse leaves the form?

Question

I have a form with a lot of controls on it. How can I detect when the mouse leaves the form? I've tried wiring up a MouseLeave event for every single control and the form, but that does not work because those events fire all the time as the mouse passes over controls. Is there a way that actually works.?

Answer 1

The only reliable way I know of is a timer. Here's sample code that tweaks the opacity on a roll-over:

  public partial class Form1 : Form {
    Timer timer1 = new Timer();
    public Form1() {
      InitializeComponent();
      this.Opacity = 0.10;
      timer1.Tick += new EventHandler(timer1_Tick);
      timer1.Interval = 200;
      timer1.Enabled = true;
    }

    void timer1_Tick(object sender, EventArgs e) {
      Point pos = Control.MousePosition;
      bool inForm = pos.X >= Left && pos.Y >= Top && pos.X < Right && pos.Y < Bottom;
      this.Opacity = inForm ? 0.99 : 0.10;
    }
  }

Answer 2

You should listen:

• MouseLeave events of all controls of the form
• MouseLeave event of the form

Just link your listeners to a function that checks whether the cursor is in the forms client are or not.

Try this:

    protected override void OnControlAdded(ControlEventArgs e)
    {
        SubscribeEvents(e.Control);
        base.OnControlAdded(e);
    }

    protected override void OnControlRemoved(ControlEventArgs e)
    {
        UnsubscribeEvents(e.Control);
        base.OnControlRemoved(e);
    }

    private void SubscribeEvents(Control control)
    {
        control.MouseLeave += new EventHandler(control_MouseLeave);
        control.ControlAdded += new ControlEventHandler(control_ControlAdded);
        control.ControlRemoved += new ControlEventHandler(control_ControlRemoved);

        foreach (Control innerControl in control.Controls)
        {
            SubscribeEvents(innerControl);
        }
    }

    private void UnsubscribeEvents(Control control)
    {
        control.MouseLeave -= new EventHandler(control_MouseLeave);
        control.ControlAdded -= new ControlEventHandler(control_ControlAdded);
        control.ControlRemoved -= new ControlEventHandler(control_ControlRemoved);

        foreach (Control innerControl in control.Controls)
        {
            UnsubscribeEvents(innerControl);
        }
    }

    private void control_ControlAdded(object sender, ControlEventArgs e)
    {
        SubscribeEvents(e.Control);
    }

    private void control_ControlRemoved(object sender, ControlEventArgs e)
    {
        UnsubscribeEvents(e.Control);
    }

    protected override void OnMouseLeave(EventArgs e)
    {
        CheckMouseLeave();
        base.OnMouseLeave(e);
    }

    private void control_MouseLeave(object sender, EventArgs e)
    {
        CheckMouseLeave();
    }

    private void CheckMouseLeave()
    {
        Point pt = PointToClient(Cursor.Position);

        if (ClientRectangle.Contains(pt) == false)
        {
            OnMouseLeftFrom();
        }
    }

    private void OnMouseLeftFrom()
    {
        Console.WriteLine("Mouse left the form");
    }