                         } else {
                             // 或放个默认的图片
                             let defaultImage = tailDirection == .Left ? UIImage(named: "left_tail_image_bubble")! : UIImage(named: "right_tail_image_bubble")!
+
                             dispatch_async(dispatch_get_main_queue()) {
                                 completion(loadingProgress: preloadingPropgress, image: defaultImage)
                             }

                completion(loadingProgress: preloadingPropgress, image: thumbnail)

            } else {
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
                    if let message = messageWithMessageID(messageID, inRealm: Realm()) {
                        if let blurredThumbnailImage = blurredThumbnailImageOfMessage(message) {
                            let bubbleBlurredThumbnailImage = blurredThumbnailImage.bubbleImageWithTailDirection(tailDirection, size: size).decodedImage()


                let fileName = message.localAttachmentName

                dispatch_async(self.cacheQueue) {

                    // 再看看是否已有地图图片文件

