Question

您好我正在尝试使用NSURLConnection委托方法将存储在服务器上的属性列表添加到我的设备上。

我在Jeff LaMarche的iOS 3书中看到了一些教程，基本上我试图实现这些方法。

这些是实施方法

但我总是不断得到：“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];
    }

}

我在控制台上获得了上述输出。有人能告诉我从哪里开始解决这个问题吗？

fileFetcher.m - [fileFetcher connection：didReceiveResponse：] 183
fileFetcher.m - [fileFetcher connection：didReceiveData：] 190
收到的数据为零 fileFetcher.m - [fileFetcher connectionDidFinishLoading：] 215
成功了！收到0字节的数据
将收到的数据转换为propertyList
时出错流有太少的字节
fileFetcher.m - [fileFetcher connectionDidFinishLoading：] 236

非常感谢。

Answer 1

在retrieveFileFromServer中异步设置后，receiveData的最简单原因是nil，如果它被作为弱引用而被删除。

当您分配/初始化本地“数据”变量时，您创建一个强引用，但是然后将其分配给归零弱引用并从方法返回，导致“数据”超出范围，仅丢失强引用并导致弱引用receivedData被淘汰。

iOS 5：pList的异步rettrieval - 接收数据总是0字节

1 个答案: