WM_DESTROY top-level constant Null safety
Sent when a window is being destroyed.
It is sent to the window procedure of the window being destroyed after the window is removed from the screen.
This message is sent first to the window being destroyed and then to the child windows (if any) as they are destroyed. During the processing of the message, it can be assumed that all child windows still exist.
const WM_DESTROY = 0x0002;