ios7下，NSURLSessionUploadTask和NSURLSessionDownloadTask的奇怪行为

今天通过DEBUG发现一个现象

如果创建下载任务时，调用的是带block的方法：

- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request completionHandler:(void (^)(NSURL *location, NSURLResponse *response, NSError *error))completionHandler;

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                              didFinishDownloadingToURL:(NSURL *)location;

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                                           didWriteData:(int64_t)bytesWritten
                                      totalBytesWritten:(int64_t)totalBytesWritten
                              totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite;

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                                      didResumeAtOffset:(int64_t)fileOffset
                                     expectedTotalBytes:(int64_t)expectedTotalBytes;

更奇怪的是，NSURLSessionUploadTask的行为并不一致，如果调用带block的方法：

- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromData:(NSData *)bodyData completionHandler:(void (^)(NSData *data, NSURLResponse *response, NSError *error))completionHandler;

这个方法不会被调用：

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
                           didCompleteWithError:(NSError *)error;

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
                                didSendBodyData:(int64_t)bytesSent
                                 totalBytesSent:(int64_t)totalBytesSent
                       totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend;

ios7下，NSURLSessionUploadTask和NSURLSessionDownloadTask的奇怪行为

原文：http://blog.csdn.net/kyfxbl/article/details/18680037