调用代码使APP退出进入iPhone手机主屏幕界面

第一种方法：    [[UIApplication sharedApplication]
     performSelector:@selector(suspend)];

第二种方法： 
- (void)exitApplication {
        AppDelegate *app = [UIApplication sharedApplication].delegate;
        UIWindow *window = app.window;
        [UIView animateWithDuration:1.0f animations:^{
            window.alpha = 0;
        } completion:^(BOOL finished) {
            exit(0);//退出APP
        }];
    }