异步 NSURLConnection 抛出 EXC_BAD_ACCESS

我不太确定为什么我的代码抛出 EXC_BAD_ACCESS，我遵循了 Apple 文档中的指南：

-(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!");
    }

}

和我的委托方法

#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];
}

我在 didReceiveData 上收到 EXC_BAD_ACCESS。即使该方法仅包含 NSLog，我也会收到错误。

注意：receivedData 是我的头文件中的 NSMutableData*

Use NSZombie启用断点并检查哪个是释放的对象。

另请检查：

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