如何重试基于块的URL请求

我使用iOS7的新的URL请求方法来获取数据，如下所示：

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self.baseUrl stringByAppendingString:path]]]; NSURLSessionDataTask *dataTask = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response; NSUInteger responseStatusCode = [httpResponse statusCode]; if (responseStatusCode != 200) { // RETRY (??????) } else completionBlock(results[@"result"][symbol]); }]; [dataTask resume]; 

不幸的是，我不时得到HTTP响应，指出服务器不可达（ response code != 200 ），需要重新发送相同的请求到服务器。

如何才能做到这一点？ 我如何才能完成我的代码片段上面我的评论// RETRY ？

在我的例子中，成功获取后调用完成块。 但是我怎么能再次发送相同的请求？

谢谢！

Answer 1

把你的请求代码放在一个方法中，并在dispatch_async块中再次调用它;）

 - (void)requestMethod { NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self.baseUrl stringByAppendingString:path]]]; __weak typeof (self) weakSelf = self; NSURLSessionDataTask *dataTask = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response; NSUInteger responseStatusCode = [httpResponse statusCode]; if (responseStatusCode != 200) { dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul), ^{ [weakSelf requestMethod]; }); } else completionBlock(results[@"result"][symbol]); }]; [dataTask resume]; } 

Answer 2

最好有一个重试计数器来防止你的方法永远运行：

 - (void)someMethodWithRetryCounter:(int) retryCounter { if (retryCounter == 0) { return; } retryCounter--; NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self.baseUrl stringByAppendingString:path]]]; __weak __typeof(self)weakSelf = self; NSURLSessionDataTask *dataTask = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { NSHTTPURLResponse* httpResponse = (NSHTTPURLResponse*)response; NSUInteger responseStatusCode = [httpResponse statusCode]; if (responseStatusCode != 200) { [weakSelf someMethodWithRetryCounter: retryCounter]; } else completionBlock(results[@"result"][symbol]); }]; [dataTask resume]; } 

它应该被称为以下方式：

 [self someMethodWithRetryCounter:5];