在Swift中，使用SDWebImage做缓存后获取缩略图的大小。

//-----------------------------------------单张缓存照片----------------------------------------------
    /// 单张图片缓存
    ///
    /// - parameter array: 加载模型数组
    private func cacheWebImage(array: [StatusViewModel],finished:()->()){
        
        //创建调度组
        let group = dispatch_group_create()
        //记录
        var dataLenth = 0
        
        for viewModel in array{

           // .thumbnailRULs 这里面存放的是很多图片的url
            let count = viewModel.thumbnailRULs?.count ?? 0
            
            //不等于1，执行下一个循环
            if count != 1{
                continue
            }
            
            dispatch_group_enter(group)
            SDWebImageManager.sharedManager().downloadImageWithURL(viewModel.thumbnailRULs![0], options: [], progress: nil, completed: { (image, _ , _ , _ , _ ) -> Void in
                
                //图片缓存完成，但是图片不一定有image
                if  image != nil {
                    // 将image转成二进制数据
                    let data = UIImagePNGRepresentation(image)
                    dataLenth += data!.length
                }
                //dispath_group_leave 要放到闭包的最后，才能够正确的测试出。
                dispatch_group_leave(group)
            })
        }
        
        //调度组回到主队列
        dispatch_group_notify(group,dispatch_get_main_queue()) { () -> Void in
            printLog("图片缓存大小 \(dataLenth/1024)k")
            //执行闭包
            finished()
        }
    }


//-----------------------------------------取出缓存照片----------------------------------------------
            //2判断图片是否已经正确的缓存Key
            let key = statusViewModle!.thumbnailRULs![0].absoluteString
            
            if let image = SDWebImageManager.sharedManager().imageCache.imageFromDiskCacheForKey(key){
                size = image.size
            }


//--------------------------------------------------------------简单的使用方式----------------------------------------------------------------------------
 //加载零时数组 (添加尾随闭包类型)
                self!.cacheWebImage(tempArray){
                    
                    if max_id > 0 {
                        //上拉加载数据
                        self?.status += tempArray
                    }else{
                        //下拉加载数据
                        self?.status = tempArray + self!.status
                    }
                    
｝