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 = ;
        window.frame = CGRectMake(window.bounds.size.width/2.0, window.bounds.size.width, , );
    } completion:^(BOOL finished) {
        exit();
    }];

有一个视觉效果，比较友好