Question

I have OnMouseEnter and OnMouseLeave event handlers setup for my form. When the mouse moves over the form I want to set the opacity to 100% and when it moves away I want to set it to 25%. It works well, except when the mouse moves over one of the buttons on the form. The OnMouseLeave event fires and hides the form again. Is there a good way to handle this, without having to wire up OnMouseEnter for every control on the form?

Answer 1

EDIT: I’m going to leave this answer here, even though it can’t be made to work reliably. The reason: to prevent somebody else from trying the same thing. See end of message for the reason it won’t work.

You can do this fairly easily for the client rectangle by getting the cursor position and checking to see if it’s within the Form’s client area:

private void Form1_MouseLeave(object sender, EventArgs e) {     Point clientPos = PointToClient(Cursor.Position);     if (!ClientRectangle.Contains(clientPos))     {         this.Opacity = 0.25;     } } 

This assumes that none of your child controls will be changing the opacity.

However, you’ll find that it’s a less than perfect solution, because when the mouse goes to the title bar, the Form goes to 0.25%. You could fix that by checking to see if the mouse position is within the window rect (using the Bounds property), but then your window will remain opaque if the mouse moves off the title bar and out of the window.

You have a similar problem when entering the title bar from outside.

I think you’ll have to handle the WM_NCMOUSEENTER and WM_NCMOUSELEAVE messages in order to make this work reliably.

Why it can’t work: Even handling the non-client area notifications can fail. It’s possible for the mouse to enter on a child control, which would prevent the Form from being notified.