C# WindowsForms - Hide control after clicking outside of it

Question

C# WindowsForms - Hide control after clicking outside of it

I have a picturebox (f.e. picturebox1) which is not visible as default. When I click a button (let's say button1) the picturebox1 will show up. Now -> I need the picturebox1 to become hidden again when I click outside of it (on form itself or any other control). It works the same as a contextmenu would work.

I have no idea how to do it since any "Click_Outside" event doesn't exist. Is there any simple way to do this? Thanks.

Answer 1

Here is a simple solution, albeit not one that is totally easy to fully understand as it does involve catching the WndProc event and using a few constants from the Windows inderds..:

This is the obvious part:

private void button1_Click(object sender, EventArgs e)
{
    pictureBox1.Show();
}

Unfortunately we can't use the pictureBox1.LostFocus event to hide the Picturebox.

That is because only some controls can actually receive focus when clicking them; a Button or other interactive controls like a ListBox, a CheckBox etc can, too.

But a Panel, a PictureBox and also the Form itself can't receive focus this way. So we need a more global solution.

As ever so often the solution comes form the depths of the Windows message system:

const int WM_PARENTNOTIFY = 0x210;
const int WM_LBUTTONDOWN = 0x201;

protected override void WndProc(ref Message m)
{
    if (m.Msg == WM_LBUTTONDOWN || (m.Msg == WM_PARENTNOTIFY && 
        (int)m.WParam == WM_LBUTTONDOWN))
        if (!pictureBox1.ClientRectangle.Contains( 
                         pictureBox1.PointToClient(Cursor.Position))) 
            pictureBox1.Hide();
    base.WndProc(ref m);
}

Note that we need to make sure that you can still clcik on the PictureBox itself; so we check if the mouse is inside its ClientRectangle..

Simply add this to the form code and every click outside the PictureBox will hide it.