iOS 创建子线程方法

方法1：performSelectorOnMainThread
[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:NO];

方法2：dispatch_async(dispatch_get_main_queue(), ^{ ... }

dispatch_async(dispatch_get_global_queue(0, 0), ^{
// 处理耗时操作的代码块...

//通知主线程刷新
dispatch_async(dispatch_get_main_queue(), ^{
//回调或者说是通知主线程刷新，
});

});