AlamofireImage磁盘缓存不起作用 [英] AlamofireImage Disk Cache not working

问题描述

我想使用AlamofireImage从URL下载图像，然后将其缓存在设备磁盘空间上。我阅读了有关此内容的几篇文章，发现AlamofireImage在 ImageDownloader 类。在此SO答案中，

I want to use AlamofireImage to download images from an url and then cache it on the device disk space. I read several posts about this and found out that AlamofireImage supports this with the help of the ImageDownloader class. The most interesting information was given in this SO answer

所以我尝试为ImageDownloader设置自定义NSURLCache，以便它将图像直接缓存到磁盘。我通过将内存容量设置为0来做到这一点。然后使用此自定义ImageDownloader下载图像。我为磁盘路径指定的文件夹是在磁盘上创建的，但不幸的是，该文件夹保持为空，并且图像没有以任何方式进行缓存。

So I tried to set a custom NSURLCache for the ImageDownloader so that it would cache the images directly to the disk. I did that by setting the memory capacity to 0. Then I use this custom ImageDownloader to download an image. The folder that I specified for the disk path is created on the disk but unfortunately it stays empty and the image is not cached in any way.

**编辑：**重要的是要注意，缓存的响应不是保存在缓存目录的文件夹中，而是保存在该文件夹旁边的数据库文件中。

** ** It is important to notice that the cached responses are not saved in the folder in the caches directory but in a database file next to the folder.

有人可以告诉我我这里做错了吗？非常感谢您的阅读！

Can anybody tell me what I am doing wrong here? Thanks very much for reading!

func diskImageDownloader(diskSpaceMB: Int = 100) -> ImageDownloader {

    let diskCapacity = diskSpaceMB * 1024 * 1024
    let diskCache = NSURLCache(memoryCapacity: 0, diskCapacity: diskCapacity, diskPath: "alamofireimage_disk_cache")
    let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
    configuration.URLCache = diskCache
    let downloader = ImageDownloader(configuration: configuration)
    UIImageView.af_sharedImageDownloader = downloader

    return downloader
}

func getProfileImage(atURL url: String, onComplete: SRServiceResponse<UIImage> -> Void) {
    guard let imageURL = NSURL(string: url) else
    {
        // TODO: Fail here
        return
    }

    let request = NSURLRequest(URL: imageURL)

    let imageDownloader = self.diskImageDownloader()

    imageDownloader.downloadImage(URLRequest: request) { (response) in
        switch response.result
        {
        case .Success(let image):
            // Do something
        case .Failure(let error):
            // Do something
        }
    }
}

推荐答案

要实现目标，请使 NSURLCache 用作磁盘缓存，实际上是自定义设置存储图像的到期日期：

To reach your goal make your NSURLCache which you use as diskCache really custom to set your own expiration date for the stored images:

class DiskCache: NSURLCache {
    private let constSecondsToKeepOnDisk = 30*24*60*60 // 30 days

    override func storeCachedResponse(cachedResponse: NSCachedURLResponse, forRequest request: NSURLRequest) {
        var customCachedResponse = cachedResponse
        // Set custom Cache-Control for Image-Response
        if let response = cachedResponse.response as? NSHTTPURLResponse,
            let contentType = response.allHeaderFields["Content-Type"] as? String,
            var newHeaders = response.allHeaderFields as? [String: String] where contentType.containsString("image") {
            newHeaders["Cache-Control"] = "public, max-age=\(constSecondsToKeepOnDisk)"
            if let url = response.URL, newResponse = NSHTTPURLResponse(URL: url, statusCode: response.statusCode, HTTPVersion: "HTTP/1.1", headerFields: newHeaders) {
                customCachedResponse = NSCachedURLResponse(response: newResponse, data: cachedResponse.data, userInfo: cachedResponse.userInfo, storagePolicy: cachedResponse.storagePolicy)
            }
        }
        super.storeCachedResponse(customCachedResponse, forRequest: request)
    }
}

而不是每次重新使用共享实例时都创建新的 ImageDownloader 调用 downloadImage 方法： UIImageView.af_sharedImageDownloader.downloadImage（URLRequest：request）

Instead of creating a new ImageDownloader every time you could reuse the shared instance to call the downloadImage method: UIImageView.af_sharedImageDownloader.downloadImage(URLRequest: request)

这篇关于AlamofireImage磁盘缓存不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！