ios - 委托(delegate)在操作期间释放

Question

我正在寻找解决以下问题的解决方案:

我有一个在后台下载图像的 NSOperation:

@protocol CoreImageDownloadingOperationDelegate <NSObject>

@required
-(void) handleResponse:(UIImage*) response;
-(void) handleException:(MobileServiceException*) exception;

@end

@interface CoreImageDownloadingOperation : NSOperation{
}

-(id) initWithDelegate:(id<CoreImageDownloadingOperationDelegate>)del andImageID: (NSString *) image;

@property (nonatomic, assign) id <CoreImageDownloadingOperationDelegate> delegate;

当下载完成后，调用委托(delegate)方法，将图片设置到imageView:

pragma mark - overridden from NSOperation
- (void) main {

    if (self.isCancelled)
        return;

    @autoreleasepool {

        @try {

            UIImage* image = [[CoreEnvironment sharedInstance] getImageFromServer: [imageID stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];

            if (self.isCancelled)
                return;

            if(delegate){
                [delegate handleResponse:image];
            }
            else
                NSLog(@"CachedImageView already deallocated");

        }@catch (NSException *exception) {

            TestLog(@"%@", exception.reason);

            if (self.isCancelled)
                return;

            if(delegate && [exception isKindOfClass:[MobileServiceException class]])
                [delegate handleException:(MobileServiceException*)exception];

        }
    }
}

问题是:当我在下载图像时转到另一个页面时，cachedImageView被释放，但是当imageDownloadingOperation完成下载时，委托(delegate)不为零，并且它正在尝试处理Response...当然我得到了消息发送到已解除分配...

我在 CachedImageView 中像这样分配初始化操作:

CoreImageDownloadingOperation* imageDownloadingOperation = [[CoreImageDownloadingOperation alloc] initWithDelegate:self andImageID:imageKey];

或:

-[CachedImageView isKindOfClass:]: message sent to deallocated instance 0x18868550

Answer 1

The problem is: when I go to another page while the image is downloading, the cachedImageView is deallocated

通常的处理方法是在 CachedImageView 的 dealloc 中将自己作为委托(delegate)删除。喜欢

// in CachedImageView
- (void)dealloc {
  // CachedImageView keeps a reference to the operation
  // called imageDownloadingOperation
  imageDownloadingOperation.delegate = nil;
  [super dealloc];
}