Question

I need to update a control only whenever the mouse moves over it with the left mouse button pressed. I would normally simply check for the e.Button property, but it is unavailable in the MouseEnter event.

void MyControl_MouseEnter(object sender, EventArgs e)
    {
        // MouseEventArgs needed to check this

        // if (e.Button == MouseButtons.Left)
        // {
        //     update MyControl
        // }
    }

How would you accomplish this?

Answer 1

Use the static Control.MouseButtons property. For example:

    private void panel1_MouseEnter(object sender, EventArgs e) {
        if (Control.MouseButtons == MouseButtons.Left) {
            // etc...
        }
    }

This is very difficult to get going, whatever the user clicks on to get the mouse button pressed is going to capture the mouse, preventing the control’s MouseEnter event from firing. It is also UI that’s completely undiscoverable to the user. Do consider a better mouse trap.