Xpre 8或更高版本•Swift 3或更高版本
同步：
if let filePath = Bundle.main.path(forResource: "imageName", ofType: "jpg"), let image = UIImage(contentsOfFile: filePath) { imageView.contentMode = .scaleAspectFit imageView.image = image}异步地：
创建带有完成处理程序的方法以从您的网址获取图像数据
func getData(from url: URL, completion: @escaping (Data?, URLResponse?, Error?) -> ()) { URLSession.shared.dataTask(with: url, completionHandler: completion).resume()}创建一种下载图像的方法（启动任务）
func downloadImage(from url: URL) { print("Download Started") getData(from: url) { data, response, error in guard let data = data, error == nil else { return } print(response?.suggestedFilename ?? url.lastPathComponent) print("Download Finished") DispatchQueue.main.async() { [weak self] in self?.imageView.image = UIImage(data: data) } }}用法：
override func viewDidLoad() { super.viewDidLoad() // Do any additional setup after loading the view, typically from a nib. print("Begin of pre") let url = URL(string: "https://cdn.arstechnica.net/wp-content/uploads/2018/06/macOS-Mojave-Dynamic-Wallpaper-transition.jpg")! downloadImage(from: url) print("End of pre. The image will continue downloading in the background and it will be loaded when it ends.")}扩展名 ：
extension UIImageView { func downloaded(from url: URL, contentMode mode: UIViewContentMode = .scaleAspectFit) { // for swift 4.2 syntax just use ===> mode: UIView.ContentMode contentMode = mode URLSession.shared.dataTask(with: url) { data, response, error in guard let httpURLResponse = response as? HTTPURLResponse, httpURLResponse.statusCode == 200, let mimeType = response?.mimeType, mimeType.hasPrefix("image"), let data = data, error == nil, let image = UIImage(data: data) else { return } DispatchQueue.main.async() { [weak self] in self?.image = image } }.resume() } func downloaded(from link: String, contentMode mode: UIViewContentMode = .scaleAspectFit) { // for swift 4.2 syntax just use ===> mode: UIView.ContentMode guard let url = URL(string: link) else { return } downloaded(from: url, contentMode: mode) }}用法：
imageView.downloaded(from: "https://cdn.arstechnica.net/wp-content/uploads/2018/06/macOS-Mojave-Dynamic-Wallpaper-transition.jpg")
