iOS学习之问题：后台线程修改自动布局引擎

错误代码：
This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release.
原因：一个后台线程修改自动布局引擎,这可能导致引擎腐败和奇怪的崩溃
解决方法：把需要更新UI的放在的主线程就好了

//在主线程上执行didThread:，waitUntilDone表示是否在当前线程等待该方法执行完成
[self performSelectorOnMainThread:@selector(didThread) withObject:@"11" waitUntilDone:NO];
- (void)didThread{
    if ([NSThread isMainThread]) {
        NSLog(@"2.主线程");
        //这里写主线程要写的代码
    }
}