Ios NSURLConnectionDataDelegate和NSURLConnectionDownloadDelegate实现这两个功能时工作不正常

我想实现两个代理。在实现这两个

NSURLConnectionDataDelegate

时，将调用两个方法。如果我正在删除

nsurconnectionDownloadDelegate

方法，则

nsurconnectionDataDelegate

方法工作正常。我不明白原因。下面是代码

-(void)downloadImageFromServer
{
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http:/*************/-yqaDz5cGzAY/USm27B4zbOI/AAAAAAAADEA/3sgkCfGNwqw/s1600/lion_hd_wallpaper.jpg"]];

    NSURLConnection *conn = [NSURLConnection connectionWithRequest:request delegate:self];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    self.mData = [NSMutableData data];

    NSLog(@"http header fields %@", [(NSHTTPURLResponse*)response allHeaderFields]);

    NSDictionary *headerFields = [(NSHTTPURLResponse*)response allHeaderFields];

    long int dataLength = [[headerFields valueForKey:@"Content-Length"] intValue];

    self.progress = [NSProgress progressWithTotalUnitCount:dataLength];

    [_progress addObserver:self
            forKeyPath:@"fractionCompleted"
               options:NSKeyValueObservingOptionNew
               context:NULL];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [_mData appendData:data];

    self.ImageViewer.image = [UIImage imageWithData:_mData];
}
- (void)connection:(NSURLConnection *)connection didWriteData:(long long)bytesWritten totalBytesWritten:(long long)totalBytesWritten expectedTotalBytes:(long long) expectedTotalBytes
{
    NSLog(@"DOwnloading..");
}

---

您是否实现了连接：didFailWithError:方法？是的，实现了。这也没有被调用。关于.h文件，您是否符合NSURLConnectDelegate？这可能是一个线索（来自文档）“NSURLConnectionDownloadDelegate协议描述了应该由NSURLConnection实例的委托实现的方法，这些实例是使用报摊工具包的downloadWithDelegate:方法创建的。”@改革者使三位代表都符合要求。