if ([[UIDevice currentDevice] respondsToSelector:@selector(setOrientation:)]) {
        SEL selector = NSSelectorFromString(@"setOrientation:");
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[UIDevice instanceMethodSignatureForSelector:selector]];
        [invocation setSelector:selector];
        [invocation setTarget:[UIDevice currentDevice]];
        int val = orientation;
        [invocation setArgument:&val atIndex:2];
        [invocation invoke];
    }

这段代码可以用来在用户已经锁定屏幕旋转的情况下, 进行强制旋转屏幕, 虽然这样用并不明智, 但是为了满足需求, 确实需要使用这样的方法, 在近期开发过程中发现了这样的问题, 在APP从后台切入前台后的这个方法中:

  - (void)applicationDidBecomeActive:(UIApplication *)application

进行强制屏幕旋转会造成

- (void)applicationDidBecomeActive:(UIApplication *)application;
- (void)applicationWillResignActive:(UIApplication *)application;
- (void)applicationDidEnterBackground:(UIApplication *)application;
- (void)applicationWillEnterForeground:(UIApplication *)application;

会造成这几个方法再执行一遍;

最终的现象就是前后台通知回调走了两次, 从而造成各种莫名其妙的bug, 所以建议这种调用苹果私有API的情况尽量不要出现