iOS 5：pList的異步檢索 - 接收到的數據總是0字節

嗨我試圖使用NSURLConnection委託方法獲取存儲在服務器上的屬性List到我的設備。iOS 5：pList的異步檢索 - 接收到的數據總是0字節

我在Jeff LaMarche的iOS 3書中看到了一些教程，基本上我試圖實現這些方法。

這些都是實現方法

但是，我一直不斷收到：「收到0字節的數據，」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]; 
    } 

}

即時得到控制檯上面的輸出。有人可以給我任何想法從哪裏開始解決這個問題嗎？

fileFetcher.m - [fileFetcher連接：didReceiveResponse：] 183
fileFetcher.m - [fileFetcher連接：didReceiveData：] 190
接收數據是零
fileFetcher.m - [fileFetcher connectionDidFinishLoading：] 215
成功了！接收的0字節的數據
的有接收到一個對propertyList
流轉換數據具有字節太少
fileFetcher.m錯誤 - [fileFetcher connectionDidFinishLoading：] 236和

感謝。

來源

2012-01-26 banditKing

receivedData不弱，是嗎？ –

是的，它很弱。那就是那個神聖的問題。哇，它的奇怪，我花了大約1天的時間來調試這個東西！ iOS 5的這些變化讓我瘋狂！非常感謝。您可以「回答」我的問題，以便我可以接受接受您的答案。 – banditKing

添加了一個更詳細的答案，爲什麼會發生這種情況。 –

在retrieveFileFromServerAsynchronously中設置receivedData的最簡單原因將是零，如果它被拒絕是一個弱引用。

當你分配/ init本地「數據」變量時，你創建一個強引用，但是你將它賦值給一個歸零弱引用並從方法返回，導致「數據」超出範圍，只有強有力的參考，並導致弱參考receivedData被清空。

來源

2012-01-26 19:48:30

iOS 5：pList的異步檢索 - 接收到的數據總是0字節

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