以下代码欲在NSOperation子线程中异步请求网络数据,请在注释处写上一段代码以满足要求。finished_代表异步请求结束的标志变量。
请选出有作用的选项:【多选】()
-(void)start { if (![self isCancelled]) { connection_ = [[NSURLConnection alloc]initWithRequest: [NSURLRequest requestWithURL:download_url cachePolicy:NSURLRequestReloadlgnoringLocalCacheData timeoutlnterval:15]delegate:self]; if (connection_ != nil) { executing_ = YES; } else { finished_ = YES; } while (!finished_) { //代码加入处 } } else { finished_ = YES; } }