Invoked automatically to inform the window that it has become the key window; never invoke this method directly.
This method reestablishes the window’s first responder, sends the
becomeKeyWindow message to that object if it responds, and posts an
didBecomeKeyNotification to the default notification center.
Managing Key Status
var isKeyWindow: Bool
A Boolean value that indicates whether the window is the key window for the application.
Moves the window to the front of the screen list, within its level, and makes it the key window; that is, it shows the window.
Invoked automatically when the window resigns key window status; never invoke this method directly.