ios - NSURLSessionDownloadDelegate 协议(protocol)的错误信息

Question

我实际上是在处理下载/上传文件并跟踪进度。它运作良好。但是，我只是想知道如果出现问题怎么办，而且我在该委托(delegate)中没有看到任何处理错误的方法。以下是 NSURLSessionDownloadDelegate 中的方法:

/*
 * Messages related to the operation of a task that writes data to a
 * file and notifies the delegate upon completion.
 */
@protocol NSURLSessionDownloadDelegate <NSURLSessionTaskDelegate>

/* Sent when a download task that has completed a download.  The delegate should 
 * copy or move the file at the given location to a new location as it will be 
 * removed when the delegate message returns. URLSession:task:didCompleteWithError: will
 * still be called.
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                              didFinishDownloadingToURL:(NSURL *)location;

@optional
/* Sent periodically to notify the delegate of download progress. */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                                           didWriteData:(int64_t)bytesWritten
                                      totalBytesWritten:(int64_t)totalBytesWritten
                              totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite;

/* Sent when a download has been resumed. If a download failed with an
 * error, the -userInfo dictionary of the error will contain an
 * NSURLSessionDownloadTaskResumeData key, whose value is the resume
 * data. 
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                                      didResumeAtOffset:(int64_t)fileOffset
                                     expectedTotalBytes:(int64_t)expectedTotalBytes;

@end

只是想知道如何返回错误消息，谢谢。

Answer 1

让您的代表符合 NSURLSessionTaskDelegate并实现:

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

EDIT 以进一步澄清，请参阅 the doc for NSURLSessionDownloadDelegate ，请注意靠近顶部的地方:

In addition to these methods, be sure to implement the methods in the NSURLSessionTaskDelegate and NSURLSessionDelegate protocols to handle events common to all task types and session-level events, respectively.

想法是 url session 的委托(delegate)可以符合任何这些协议(protocol)。您正在寻找的方法，即指示错误的方法，只是比下载任务更通用，它可能发生在任何类型的 session 任务上，因此他们将其放在更抽象的协议(protocol)中。