Question

我现在在斯坦福iOS Swift Assignment 6上，其中一项所需任务是使用URLCache缓存本地磁盘上的映像。经过几天的谷歌搜索，我仍然无法弄清楚如何使用它。如果有人能指点我一个好导游，那会很有帮助！

在尝试理解官方文档后，我的代码就像这样。官方文档没有我可以参考的示例代码，这没有任何帮助：（

let urlCache = URLCache.shared

所需的任务是设置缓存并指定大小限制。我尝试初始化URLCache并传递参数中的大小。它工作，但存储和获取缓存似乎不起作用。如果每次启动应用程序（或视图控制器）时初始化URLCache，是否会忽略先前创建和存储的缓存？

我认为此代码没有问题？从缓存中读取数据

if let cachedURLResponse = urlCache.cachedResponse(for: URLRequest(url: url)) {
    if let fetchedImage = UIImage(data: cachedURLResponse.data) {
        image = fetchedImage
    }
}

我把数据写入缓存

urlCache.storeCachedResponse(CachedURLResponse(response: URLResponse(), data: imageData), for: URLRequest(url: url))

如何正确初始化URLResponse？我查看了init方法，它还要求将url作为参数传入。发现这很奇怪，因为url也在URLRequest（）中。我做错了吗？

非常感谢有用的建议！

Answer 1

您可以通过使用URLSession请求图像数据然后使用其完成处理程序中提供的数据和响应来使用URLCache，例如：

import UIKit

class GalleryCollectionViewController: UICollectionViewController, UICollectionViewDragDelegate, UICollectionViewDropDelegate, UICollectionViewDelegateFlowLayout {

 // MARK: - Model

 var gallery: Gallery?

 // MARK: - Properties

 private var cache = URLCache.shared
 private var session = URLSession(configuration: .default)

 override func viewDidLoad() {
    super.viewDidLoad()
    cache = URLCache(memoryCapacity: 100, diskCapacity: 100, diskPath: nil) // replace capacities with your own values
 }

 override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "GalleryCell", for: indexPath)
    if let galleryCell = cell as? GalleryCollectionViewCell {
        galleryCell.image = nil
        galleryCell.imageView.isHidden = true
        if let url = gallery?.images[indexPath.item].url {
            let request = URLRequest(url: url.imageURL) // imageURL from Utilities.swift of Stanford iOS course
            if let cachedResponse = cache.cachedResponse(for: request), let image = UIImage(data: cachedResponse.data) {
                galleryCell.image = image
                galleryCell.imageView.isHidden = false
            } else {
                DispatchQueue.global(qos: .userInitiated).async { [weak self, weak galleryCell] in
                    let task = self?.session.dataTask(with: request) { (urlData, urlResponse, urlError) in
                        DispatchQueue.main.async {
                            if urlError != nil { print("Data request failed with error \(urlError!)") }
                            if let data = urlData, let image = UIImage(data: data) {
                                if let response = urlResponse {
                                    self?.cache.storeCachedResponse(CachedURLResponse(response: response, data: data), for: request)
                                }
                                galleryCell?.image = image
                            } else {
                                galleryCell?.image = UIImage(named: "placeholder")
                            }
                            galleryCell?.imageView.isHidden = false
                        }
                    }
                    task?.resume()
                }
            }
        }
    }
    return cell
 }
}

URLCache（CS193P作业6）

1 个答案: