// 1.GCD方法，通过向主线程队列发送一个block块，使block里的方法可以在主线程中执行。dispatch_async(dispatch_get_main_queue(), ^{    //需要执行的方法});// 2.NSOperation 方法NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];  //主队列NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{    //需要执行的方法}];[mainQueue addOperation:operation];// 3.NSThread 方法[self performSelector:@selector(method) onThread:[NSThread mainThread] withObject:nil waitUntilDone:YES modes:nil];[self performSelectorOnMainThread:@selector(method) withObject:nil waitUntilDone:YES];[[NSThread mainThread] performSelector:@selector(method) withObject:nil];// 4.RunLoop方法[[NSRunLoop mainRunLoop] performSelector:@selector(method) withObject:nil];