如何在Swift中使用URLSession缓存图像 [英] How to cache images using URLSession in Swift
本文介绍了如何在Swift中使用URLSession缓存图像的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我想增强下面的代码来缓存图像,并仅在以前没有缓存过的情况下才下载它们.我似乎找不到如何使用URLSession对象执行此操作的任何好示例.
I would like to enhance the code below to cache images and only download them if they haven't been cached previously. I can't seem to find any good examples of how to use URLSession object to do this.
extension UIImageView {
func loadImageWithURL(_ url: URL) -> URLSessionDownloadTask {
let session = URLSession.shared
let downloadTask = session.downloadTask(with: url, completionHandler: { [weak self] url, response, error in
if error == nil, let url = url,
let data = try? Data(contentsOf: url), let image = UIImage(data: data) {
DispatchQueue.main.async {
if let strongSelf = self {
strongSelf.image = image
}
}
}
})
downloadTask.resume()
return downloadTask
}
}
推荐答案
已针对Swift 4更新
import UIKit
let imageCache = NSCache<AnyObject, AnyObject>()
class ImageLoader: UIImageView {
var imageURL: URL?
let activityIndicator = UIActivityIndicatorView()
func loadImageWithUrl(_ url: URL) {
// setup activityIndicator...
activityIndicator.color = .darkGray
addSubview(activityIndicator)
activityIndicator.translatesAutoresizingMaskIntoConstraints = false
activityIndicator.centerXAnchor.constraint(equalTo: centerXAnchor).isActive = true
activityIndicator.centerYAnchor.constraint(equalTo: centerYAnchor).isActive = true
imageURL = url
image = nil
activityIndicator.startAnimating()
// retrieves image if already available in cache
if let imageFromCache = imageCache.object(forKey: url as AnyObject) as? UIImage {
self.image = imageFromCache
activityIndicator.stopAnimating()
return
}
// image does not available in cache.. so retrieving it from url...
URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
if error != nil {
print(error as Any)
DispatchQueue.main.async(execute: {
self.activityIndicator.stopAnimating()
})
return
}
DispatchQueue.main.async(execute: {
if let unwrappedData = data, let imageToCache = UIImage(data: unwrappedData) {
if self.imageURL == url {
self.image = imageToCache
}
imageCache.setObject(imageToCache, forKey: url as AnyObject)
}
self.activityIndicator.stopAnimating()
})
}).resume()
}
}
用法:
// assign ImageLoader class to your imageView class
let yourImageView: ImageLoader = {
let iv = ImageLoader()
iv.frame = CGRect(x: 10, y: 100, width: 300, height: 300)
iv.backgroundColor = UIColor(red: 0.94, green: 0.94, blue: 0.96, alpha: 1.0)
iv.contentMode = .scaleAspectFill
iv.clipsToBounds = true
return iv
}()
// unwrapped url safely...
if let strUrl = "https://picsum.photos/300/300".addingPercentEncoding(withAllowedCharacters: .urlFragmentAllowed),
let imgUrl = URL(string: strUrl) {
yourImageView.loadImageWithUrl(imgUrl) // call this line for getting image to yourImageView
}
这篇关于如何在Swift中使用URLSession缓存图像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!
查看全文