Lessons-lostfocus and MessageBox

I wrote a logic error.CodeAt that time, I found the problem only when I did not think about debugging carefully. A simple logic is to use the control to determine the data on the control when the control loses focus, and then describe the error content pop-up dialog box, the key error is that you want to re-return the focus to the control after an error is found.
Control. Focus (); MessageBox. Show ("");
I forgot to focus first, and then MessageBox. Show re-triggered the focus loss event. It's depressing. It's just a dead end.

Put the focus behind show.