Ios5 异步连接泄漏

我知道这个问题已经被报道了很多次，但几乎所有的答案都与非ARC项目有关，我已经被困了好几天了。我在很多论坛和文章中都看过。我希望我能在这里找到一些帮助

我使用异步NSURLConnection请求，以便使用IOS 5和ARC下载图片，以下代码来源于《学习IPAd编程》一书：

-(void) dowloadImageAtURL:(NSURL *)URL
{
    if (URL)
    {        
        self.image = nil;
        self.receivedData = [[NSMutableData alloc] init];
        NSURLRequest *request = [NSURLRequest requestWithURL:URL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0];
        [[NSURLCache sharedURLCache] setMemoryCapacity:0];
        [[NSURLCache sharedURLCache] setDiskCapacity:0];
        NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request              // Building asynchronous connection
                                                               delegate:self
                                                              startImmediately:NO];                 // This is the key to not run the connection synchronous
        [connection scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];     // We use the current loop but it will still be asynchronous
                                                                                                    // because of the mode added to the current loop
        [connection start];
        request = nil;
    }
}

#pragma marks - NSURLConnection delegate Methods

/*
 Called when the web server responds to the request.
 When the method is called, the receivedData property is reset with a length of zero, clearing any previously stored data.
 This ensures that only the data received from the final request is captured (see NSURLConnectionDelegate reference).
 */
- (void) connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [self.receivedData setLength:0];
    NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:0 diskCapacity:0 diskPath:nil];
    [NSURLCache setSharedURLCache:sharedCache];
    sharedCache = nil;
    connection = nil;
}


/*
 Called when data is received from the network. The method can be called a multiple times during a single request.
 The data is appended to the data already stored in the receivedData property.
 */
- (void) connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [self.receivedData appendData:data];

}


/*
 Called after the request has completed all data and all data has been received. This method converts
 the data stored to a UIImage object. 
 */
- (void) connectionDidFinishLoading:(NSURLConnection *)connection
{
    self.image = [UIImage imageWithData:self.receivedData];
    self.receivedData = nil;
    connection = nil;
    NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:0 diskCapacity:0 diskPath:nil];
    [NSURLCache setSharedURLCache:sharedCache];
    sharedCache = nil;

    // Here we post a notification to the observer
    [[NSNotificationCenter defaultCenter] postNotificationName:@"com.perfectmemory.famille.imageupdated" object:self];
}


/*
 Called if an error is detected at any time during the download process.
 */
- (void) connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    self.receivedData = nil;
    connection = nil;
    NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:0 diskCapacity:0 diskPath:nil];
    [NSURLCache setSharedURLCache:sharedCache];
    sharedCache = nil;

    // Here we post a notification to the observer
    [[NSNotificationCenter defaultCenter] postNotificationName:@"com.perfectmemory.famille.imageupdated" object:self];

}

运行这段代码时，下载效果很好，但我可以看到XCode工具中存在漏洞

URLConnectionLoader:：LoaderConnectionEventQueue URLConnection:：scheduleWithRunLoop CFURLResponse URLConnectionInstanceData

我已使用以下帮助尝试解决此问题，例如清除缓存，但没有成功：

我还尝试通过以下方式释放每个相关委托方法中的连接：

connection = nil

但仍然没有成功。我真的不明白发生了什么事。我找不到未发布的对象。你能帮帮我吗？这非常令人沮丧，因为我想这种异步下载请求非常常见

先谢谢你