異步NSURLConnection的拋出EXC_BAD_ACCESS

Question

我真的不知道爲什麼我的代碼拋出一個EXC_BAD_ACCESS，我按照蘋果的文檔中的準則：

-(void)getMessages:(NSString*)stream{ 

    NSString* myURL = [NSString stringWithFormat:@"http://www.someurl.com"]; 

    NSURLRequest *theRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:myURL]]; 

    NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self]; 
    if (theConnection) { 
     receivedData = [[NSMutableData data] retain]; 
    } else { 
     NSLog(@"Connection Failed!"); 
    } 

} 

我的委託方法

#pragma mark NSURLConnection Delegate Methods 
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response 
{ 
    // This method is called when the server has determined that it 
    // has enough information to create the NSURLResponse. 

    // It can be called multiple times, for example in the case of a 
    // redirect, so each time we reset the data. 

    // receivedData is an instance variable declared elsewhere. 
    [receivedData setLength:0]; 
} 

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data 
{ 
    // Append the new data to receivedData. 
    // receivedData is an instance variable declared elsewhere. 
    [receivedData appendData:data]; 
} 

- (void)connection:(NSURLConnection *)connection 
    didFailWithError:(NSError *)error 
{ 
    // release the connection, and the data object 
    [connection release]; 
    // receivedData is declared as a method instance elsewhere 
    [receivedData release]; 

    // inform the user 
    NSLog(@"Connection failed! Error - %@ %@", 
      [error localizedDescription], 
      [[error userInfo] objectForKey:NSErrorFailingURLStringKey]); 
} 

- (void)connectionDidFinishLoading:(NSURLConnection *)connection 
{ 
    // do something with the data 
    // receivedData is declared as a method instance elsewhere 
    NSLog(@"Succeeded! Received %d bytes of data",[receivedData length]); 

    // release the connection, and the data object 
    [connection release]; 
    [receivedData release]; 
} 

我得到didReceiveData上的EXC_BAD_ACCESS。即使該方法只包含一個NSLog，我也會得到該錯誤。

注：receivedData是NSMutableData *在我的頭文件

Answer 1

使用NSZombieEnabled破發點，並檢查它是釋放對象。

同時檢查：

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response 
{ 
    if ([response expectedContentLength] < 0) 
    { 
     NSLog(@"Connection error"); 
      //here cancel your connection. 
      [connection cancel]; 
     return; 
    } 
} 

Answer 2

如果你在didRecieveData得到錯誤，無論它裏面的代碼，它看起來像你的委託被釋放？

我會檢查包含getMessages方法的對象在連接完成獲取數據之前未被釋放（或自動釋放）。

---

編輯：下圖顯示了評論，我上面的回答是錯誤的:)

的問題是在recievedData變量 - 它被提前釋放。 Mark建議在創建連接的對象的dealloc方法中釋放它，所以他值得所有的功勞！

這裏有一點小事要注意 - 如果你在dealloc方法中釋放recievedData，如果你多次調用getMessages，將會泄漏內存。你需要稍微改變的getMessages這樣：

... 
if (theConnection) { 
    [recievedData release]; // If we've been here before, make sure it's freed. 
    receivedData = [[NSMutableData data] retain]; 
} else { 
... 

Answer 3

我按照蘋果的文檔中的準則：

這是不正確的。在兩個以下，你打破了規則：

- (void)connection:(NSURLConnection *)connection 
didFailWithError:(NSError *)error 
{ 
    // release the connection, and the data object 
    [connection release]; 
    // receivedData is declared as a method instance elsewhere 
    [receivedData release]; 

    // inform the user 
    NSLog(@"Connection failed! Error - %@ %@", 
      [error localizedDescription], 
      [[error userInfo] objectForKey:NSErrorFailingURLStringKey]); 
} 

- (void)connectionDidFinishLoading:(NSURLConnection *)connection 
{ 
    // do something with the data 
    // receivedData is declared as a method instance elsewhere 
    NSLog(@"Succeeded! Received %d bytes of data",[receivedData length]); 

    // release the connection, and the data object 
    [connection release]; 
    [receivedData release]; 
} 

在這兩種情況下，你不獲得的connection對象與alloc，方法開頭new或含有copy。這些方法中您不擁有connection。你不能用這些方法釋放它。

在我看來，稍微有點不妥，你也在那裏發佈receivedData。我建議你在釋放它之後立即將實例變量設置爲零。

[receivedData release]; 
receivedData = nil; 

這樣，它不會被意外地釋放一次。

Answer 4

評論JeremyP，他在那裏說「在以下兩種情況下，你違反規則」：Sheehan Alam正在關注Apple的代碼（實際上，cut'n'paste）發現here。

我還想補充（這是一些沒有很好回答here）'構建和分析'標誌NSURLConnection（它是由一個「[NSURLConnection alloc ]「）。但是如果在NSURLConnection的[連接釋放]中放入同樣的方法，它將會崩潰。

因此，我們有一些似乎違背了內存管理的「規則」，但作品（據我所知），是蘋果公司的文檔..

Answer 5

我與設備調試時雖然沒有問題得到了同樣的錯誤在模擬中。添加下面的代碼行後釋放receivedData解決了這個問題：

receivedData = nil; 

Answer 6

我在NSURLConnection的EXC_BAD_ACCESS了異步調用。 由http://www.sudzc.com

我需要添加生成的代碼保留

receivedData = [[NSMutableData data] retain];

和回調方法沒有得到壞接入信號了。

• 如果我添加了

  if ([response expectedContentLength] < 0) { NSLog(@"Connection error"); //here cancel your connection. [connection cancel]; return; }

比我的web服務被取消，否則完美的作品。

Answer 7

雖然它沒有回答完整的問題，但我已經遇到了這個錯誤幾次，因爲我將請求的HTTPBody設置爲NSString而不是NSData。 Xcode試圖警告我。