NSEvent不起作用

NSEvent* keyEvent = [NSEvent keyEventWithType:NSKeyDown location:NSZeroPoint modifierFlags:NSCommandKeyMask timestamp:0 windowNumber:[windowNumber intValue] context:[NSGraphicsContext currentContext] characters:@"A" charactersIgnoringModifiers:nil isARepeat:NO keyCode:0];
[NSApp postEvent:keyEvent atStart:NO];