异步NSURLConnection的抛出EXC_BAD_ACCESS

Question

我真的不知道为什么我的代码抛出一个EXC_BAD_ACCESS，我按照苹果的文档中的准则：

-(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!"); 
    } 

} 

我的委托方法

#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。即使该方法只包含一个NSLog，我也会得到该错误。

注：receivedData是NSMutableData *在我的头文件

Answer 1

使用NSZombieEnabled破发点，并检查它是释放对象。

同时检查：

- (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得到错误，无论它里面的代码，它看起来像你的委托被释放？

我会检查包含getMessages方法的对象在连接完成获取数据之前未被释放（或自动释放）。

---

编辑：下图显示了评论，我上面的回答是错误的:)

的问题是在recievedData变量 - 它被提前释放。 Mark建议在创建连接的对象的dealloc方法中释放它，所以他值得所有的功劳！

这里有一点小事要注意 - 如果你在dealloc方法中释放recievedData，如果你多次调用getMessages，将会泄漏内存。你需要稍微改变的getMessages这样：

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

Answer 3

我按照苹果的文档中的准则：

这是不正确的。在两个以下，你打破了规则：

- (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]; 
} 

在这两种情况下，你不获得的connection对象与alloc，方法开头new或含有copy。这些方法中您不拥有connection。你不能用这些方法释放它。

在我看来，稍微有点不妥，你也在那里发布receivedData。我建议你在释放它之后立即将实例变量设置为零。

[receivedData release]; 
receivedData = nil; 

这样，它不会被意外地释放一次。

Answer 4

评论JeremyP，他在那里说“在以下两种情况下，你违反规则”：Sheehan Alam正在关注Apple的代码（实际上，cut'n'paste）发现here。

我还想补充（这是一些没有很好回答here）'构建和分析'标志NSURLConnection（它是由一个“[NSURLConnection alloc ]“）。但是如果在NSURLConnection的[连接释放]中放入同样的方法，它将会崩溃。

因此，我们有一些似乎违背了内存管理的“规则”，但作品（据我所知），是苹果公司的文档..

Answer 5

我与设备调试时虽然没有问题得到了同样的错误在模拟中。添加下面的代码行后释放receivedData解决了这个问题：

receivedData = nil; 

Answer 6

我在NSURLConnection的EXC_BAD_ACCESS了异步调用。 由http://www.sudzc.com

我需要添加生成的代码保留

receivedData = [[NSMutableData data] retain];

和回调方法没有得到坏接入信号了。

• 如果我添加了

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

比我的web服务被取消，否则完美的作品。

Answer 7

虽然它没有回答完整的问题，但我已经遇到了这个错误几次，因为我将请求的HTTPBody设置为NSString而不是NSData。 Xcode试图警告我。