如何使用SDWebImageManager仅在未缓存时下载图像？

Question

如何使用SDWebImageManager仅在未缓存时下载图像？

7

我需要使用SDWebImageManager的完成处理程序功能（将已下载或缓存的图像设置为黑白），因此我正在使用它而不是sd_setimage。我的问题是，我无法弄清楚如何使用SDWebImageManager下载或获取缓存版本的图像。每次重用并重新加载tableview单元格时都会重新下载图像。我尝试设置选项：SDWebImageDownloaderOptions.useNSURLCache，但没有效果。任何建议都将不胜感激！以下是我的代码：

SDWebImageManager.shared().imageDownloader?.downloadImage(with:URL(string: imgURL), options: SDWebImageDownloaderOptions.useNSURLCache, progress: nil, completed: { (image, error, cacheType, url) in 
   if image != nil {
      let beginImage = CIImage(image: image!)
      let blackNwhiteImg = beginImage?.applyingFilter("CIColorControls", withInputParameters: [kCIInputSaturationKey:0.0])
      let newImage = UIImage(ciImage: blackNwhiteImg!)
      cell.button.setImage(newImage, for: .normal)
   }
})

- lucius degeer

2个回答

5

你可以使用SDWebImageManager.shared().cachedImageExists(for: imageUrl)方法来判断一个URL是否被缓存。

然后你可以使用这个方法获取缓存键(cacheKey)。

let cacheKey = SDWebImageManager.shared().cacheKey(for: imageUrl)

有了CacheKey，您可以调用此方法，在其闭包中获取缓存的图像。

SDWebImageManager.shared().imageCache.queryDiskCache(forKey: cacheKey, done: { (image, cacheType) in

                })

- Reinier Melian

1

谢谢您的回复。那么我该如何在完成块内获取该URL的缓存图像呢？据我所知，并没有传递“image”值。 - lucius degeer

1

谢谢你的回答。了解CacheKey非常有用。我认为.loadImage就是我在寻找的东西。 - lucius degeer

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- CodeBender · Accepted Answer

更新了从缓存中拉取的答案：

SDWebImageManager.shared().loadImage(with: URL?, options: SDWebImageOptions, progress: { (Int, Int, URL?) in
    code
}, completed: { (UIImage?, Data?, Error?, SDImageCacheType, Bool, URL?) in
    code
})

为了参考，我包含了这张截图，它展示了在输入函数时XCode所呈现的注释:

另外，在SDWebImageManager文件中包含的注释:

/**
 * Downloads the image at the given URL if not present in cache or return the cached version otherwise.
 *
 * @param url            The URL to the image
 * @param options        A mask to specify options to use for this request
 * @param progressBlock  A block called while image is downloading
 *                       @note the progress block is executed on a background queue
 * @param completedBlock A block called when operation has been completed.
 *
 *   This parameter is required.
 * 
 *   This block has no return value and takes the requested UIImage as first parameter and the NSData representation as second parameter.
 *   In case of error the image parameter is nil and the third parameter may contain an NSError.
 *
 *   The forth parameter is an `SDImageCacheType` enum indicating if the image was retrieved from the local cache
 *   or from the memory cache or from the network.
 *
 *   The fith parameter is set to NO when the SDWebImageProgressiveDownload option is used and the image is
 *   downloading. This block is thus called repeatedly with a partial image. When image is fully downloaded, the
 *   block is called a last time with the full image and the last parameter set to YES.
 *
 *   The last parameter is the original image URL
 *
 * @return Returns an NSObject conforming to SDWebImageOperation. Should be an instance of SDWebImageDownloaderOperation