             loadingProgress(1.0)
 
         } else {
+            let messageID = message.messageID
+
             // 若可以，先显示 blurredThumbnailImage
 
             let thumbnailKey = "thumbnail" + imageKey

                completion(thumbnail)

            } else {
                if let blurredThumbnailImage = blurredThumbnailImageOfMessage(message) {
                    let bubblebBlurredThumbnailImage = blurredThumbnailImage.bubbleImageWithTailDirection(tailDirection, size: size)

                    self.cache.setObject(bubblebBlurredThumbnailImage, forKey: thumbnailKey)

                    completion(bubblebBlurredThumbnailImage)

                } 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")!
                    completion(defaultImage)
                }
            }


            if message.mediaType == MessageMediaType.Video.rawValue {
                imageURLString = message.thumbnailURLString
            }

            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {

