IOS 应用 退出的一个小方法

 AppDelegate * app=(AppDelegate *)[[UIApplication sharedApplication]delegate];
    UIWindow *window = app.window;
    [UIView animateWithDuration:1.0f animations:^{
        window.alpha = 0;
        window.frame = CGRectMake(window.bounds.size.width/2.0, window.bounds.size.width, 0, 0);
    } completion:^(BOOL finished) {
        exit(0);
    }];