iOS 退出应用程序

退出应用程序，方法很简单，只是动画效果没有那么好。

- (void)exitApplication {
    AppDelegate *app = [UIApplication sharedApplication].delegate;
    UIWindow *window = app.window;
    [UIView animateWithDuration:1.0 animations:^{
        window.alpha = ;
    } completion:^(BOOL finished) {
        exit();
    }];
}