Asynchronous iOS 5:pList的异步检索-接收的数据始终为0字节

嗨，我正在尝试使用NSURLConnection委托方法将存储在服务器上的属性列表获取到我的设备上

我在Jeff LaMarche的iOS 3书中看到了一些教程，基本上我正在尝试实现这些方法

这些是实现方法

但我总是收到：“收到0字节的数据”我不明白：

#pragma -NSURLCOnnection Delegate Methods

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__);
    [receivedData setLength:0];
}
//==============================================================================
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
   [receivedData appendData:data];
   NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__); 
    if(!self.receivedData)
    {
        NSLog(@"Received Data was nil");
    }
}
//==============================================================================
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{

    UIAlertView *alert1 = [[UIAlertView alloc] 
                           initWithTitle:@"Error" 
                           message:[NSString stringWithFormat:@" Connection Failed! Error: %@ ,(URL:%@)", [error localizedDescription] ,[[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]]
                           delegate:self 
                           cancelButtonTitle:@"Cancel" 
                           otherButtonTitles:nil];
    [alert1 show];


    NSLog(@"Connection failed! Error - %@ %@",[error localizedDescription],[[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
    NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__);

    NSLog(@"Succeeded! Received %d bytes of data",[self.receivedData length]);
    //Now take the data and convert it into a propertylist
    NSData *plistData = self.receivedData;
    NSPropertyListFormat format;
    NSString *error;
    id pList = [NSPropertyListSerialization propertyListFromData:plistData
                                                mutabilityOption:NSPropertyListImmutable
                                                          format:&format
                                                errorDescription:&error];


    if(!pList)
    {
        NSLog(@"There was an error converting data received into a propertyList");
        NSLog(error);
    }

    self.receivedData = nil;
    NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__);
}

-(void)retrieveFileFromServerAsynchronously
{
    NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__);
    if(![self getURLToGetFileFrom])
    {    
        UIAlertView *alert1 = [[UIAlertView alloc] 
                              initWithTitle:@"Error" 
                              message:@"InvalidPath" 
                              delegate:self cancelButtonTitle:@"Cancel" 
                              otherButtonTitles:nil];
        [alert1 show];
    }

    if(![self getFileName])
    {
        UIAlertView *alert2 = [[UIAlertView alloc] 
                               initWithTitle:@"Error" 
                               message:@"Invalid FileName" 
                               delegate:self cancelButtonTitle:@"Cancel" 
                               otherButtonTitles:nil];
        [alert2 show];


    }


    NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__);

    NSMutableString *urlString = [[NSMutableString alloc] initWithString:[self getURLToGetFileFrom]];

    [urlString appendString:[self getFileName]];
    NSLog((@"Fetching file from URL %@", urlString));

    NSURLRequest *req = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:urlString]
                                              cachePolicy:NSURLRequestUseProtocolCachePolicy 
                                          timeoutInterval:60.00 ];

    NSURLConnection *con = [[NSURLConnection alloc] initWithRequest:req delegate:self];


    if(con)
    {
        NSMutableData *data = [[NSMutableData alloc] init ];
        self.receivedData = data;
        if(!self.receivedData)
            NSLog(@"Received Data was nil");
        NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__);
    }
    else
    {
        NSLog(@"%s %s %d", __FILE__, __FUNCTION__, __LINE__);
        UIAlertView *alert = [[UIAlertView alloc] 
                              initWithTitle:@"Error" 
                              message:@"Couldn't connect to remote server" 
                              delegate:self cancelButtonTitle:@"Cancel" 
                              otherButtonTitles:nil];
        [alert show];
    }

}

我在控制台上得到上面的输出。有人能告诉我从哪里开始修理这个吗

fileFetcher.m-[fileFetcher连接：didReceiveResponse:]183
fileFetcher.m-[fileFetcher连接：didReceiveData:]190
收到的数据为零
fileFetcher.m-[fileFetcher connectiondFinishLoading:]215
成功！接收到0字节的数据
将收到的数据转换为propertyList时出错
流的字节太少
fileFetcher.m-[fileFetcher connectiondFinishLoading:]236

---

非常感谢。

异步在RetrieveFileFromServers中设置receivedData后，最简单的原因是它是否因为弱引用而被置空

---

当您alloc/init本地“data”变量时，您创建了一个强引用，但随后将其分配给一个调零弱引用并从方法返回，导致“data”超出范围，丢失唯一的强引用并导致弱引用receivedData被调零。

receivedData不是弱的，是吗？是的，它是弱的。天哪，那就是问题所在。哇，真奇怪，我花了大约一天的时间调试这个东西！！iOS 5的这些变化快把我逼疯了！！谢谢。你可以“回答”我的问题，这样我就可以接受你的答案。添加了一个更详细的答案，解释为什么会发生这种情况。