编辑为最新更改2021年9月

// It's better to use extension 
extension UIImageView {
func downloadImage(from URLString: String, with completion: @escaping (_ response: (status: Bool, image: UIImage? ) ) -> Void) {
    guard let url = URL(string: URLString) else {
        completion((status: false, image: nil))
        return
    }
    
    URLSession.shared.dataTask(with: url) { data, response, error in
        guard error == nil else {
            completion((status: false, image: nil))
            return
        }
        
        guard let httpURLResponse = response as? HTTPURLResponse,
              httpURLResponse.statusCode == 200,
              let data = data else {
            completion((status: false, image: nil))
            return
        }
        
        let image = UIImage(data: data)
        completion((status: true, image: image))
    }.resume()
}
}

快乐的鳕鱼。欢呼:)

在使用SwiftUI时，SDWebImageSwiftUI是最好的选择。

通过XCode的Swift Package Manager添加依赖:https://github.com/SDWebImage/SDWebImageSwiftUI.git

然后使用WebImage()而不是Image()

WebImage(url: URL(string: "https://nokiatech.github.io/heif/content/images/ski_jump_1440x960.heic"))

Swift 3错误处理

let url = URL(string: arr[indexPath.row] as! String)
if url != nil {
    DispatchQueue.global().async {
        let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
        DispatchQueue.main.async {
            if data != nil {
                cell.imgView.image = UIImage(data:data!)
            }else{
                cell.imgView.image = UIImage(named: "default.png")
            }
        }
    }
}

与扩展

extension UIImageView {

    func setCustomImage(_ imgURLString: String?) {
        guard let imageURLString = imgURLString else {
            self.image = UIImage(named: "default.png")
            return
        }
        DispatchQueue.global().async { [weak self] in
            let data = try? Data(contentsOf: URL(string: imageURLString)!)
            DispatchQueue.main.async {
                self?.image = data != nil ? UIImage(data: data!) : UIImage(named: "default.png")
            }
        }
    }
}

扩展使用

myImageView. setCustomImage("url")

具有缓存支持

let imageCache = NSCache<NSString, UIImage>()

extension UIImageView {

    func loadImageUsingCacheWithURLString(_ URLString: String, placeHolder: UIImage?) {

        self.image = nil
        if let cachedImage = imageCache.object(forKey: NSString(string: URLString)) {
            self.image = cachedImage
            return
        }

        if let url = URL(string: URLString) {
            URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in

                //print("RESPONSE FROM API: \(response)")
                if error != nil {
                    print("ERROR LOADING IMAGES FROM URL: \(String(describing: error))")
                    DispatchQueue.main.async { [weak self] in
                        self?.image = placeHolder
                    }
                    return
                }
                DispatchQueue.main.async { [weak self] in
                    if let data = data {
                        if let downloadedImage = UIImage(data: data) {
                            imageCache.setObject(downloadedImage, forKey: NSString(string: URLString))
                            self?.image = downloadedImage
                        }
                    }
                }
            }).resume()
        }
    }
}

为了在UITableView或UICollectionView中获得更好的性能，使用轻量级库智能惰性加载，如果你想从url异步加载图像，可以使用这种惰性加载方法

因此，在这个项目中，我们可以通过使用操作和操作队列并发优化应用程序的性能，在任何视图(UICollectionView或UITableView)中下载多个图像。以下是这个项目的重点智能延迟加载:创建图像下载服务。根据单元格的可见性优先下载。

ImageDownloadService类将创建一个单例实例，并有一个NSCache实例来缓存已下载的图像。我们已经将Operation类继承给TOperation，以便根据我们的需要修改功能。我认为就功能而言，operation子类的属性非常清楚。我们使用KVO监测操作状态的变化。

class ImageStore: NSObject { 
    static let imageCache = NSCache<NSString, UIImage>()
}

extension UIImageView {
    func url(_ url: String?) {
        DispatchQueue.global().async { [weak self] in
            guard let stringURL = url, let url = URL(string: stringURL) else {
                return
            }
            func setImage(image:UIImage?) {
                DispatchQueue.main.async {
                    self?.image = image
                }
            }
            let urlToString = url.absoluteString as NSString
            if let cachedImage = ImageStore.imageCache.object(forKey: urlToString) {
                setImage(image: cachedImage)
            } else if let data = try? Data(contentsOf: url), let image = UIImage(data: data) {
                DispatchQueue.main.async {
                    ImageStore.imageCache.setObject(image, forKey: urlToString)
                    setImage(image: image)
                }
            }else {
                setImage(image: nil)
            }
        }
    }
}

用法:

let imageView = UIImageView()
imageView.url("image url")

class Downloader {
    
    class func downloadImageWithURL(url: String) -> UIImage! {
        
        let date = NSData(contentsOf: URL(string: url)!)
        return UIImage(data: date! as Data)
    }
}

用法:

let img = Downloader.downloadImageWithURL(url: imageURL)
        self.imageView1.image = img