摘要：
回调主线程（1）NSThread1.performSelectorOnMainThread调用主线程的方法、[selfperformSelectorOnMainThread:@selector(finish)withObject:selfwaitUntilDone:NO];2.回调其她子线程也是可以的，但是不用selfperformSelector:（2）GCDdispatch_async(dis
回调主线程
（1）NSThread
1.performSelectorOnMainThread调用主线程的方法、
[self performSelectorOnMainThread:@selector(finish) withObject:self waitUntilDone:NO];
2.回调其她子线程也是可以的，但是不用
self performSelector:
（2）GCD
dispatch_async(dispatch_get_main_queue(), ^{
（3）NSOperation
NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];
[mainQueue addOperationWithBlock:^{