在Swift上从URL加载/下载图像

Question

我想从我的应用程序中的URL加载图像，因此我首先尝试使用Objective-C，但是它可以正常工作，但是对于Swift，我遇到了编译错误：

‘imageWithData’不可用：使用对象构造’UIImage（data :)’

我的功能：

@IBOutlet var imageView : UIImageView

override func viewDidLoad() {
    super.viewDidLoad()

    var url:NSURL = NSURL.URLWithString("http://myURL/ios8.png")
    var data:NSData = NSData.dataWithContentsOfURL(url, options: nil, error: nil)

    imageView.image = UIImage.imageWithData(data)// Error here
}

在Objective-C中：

- (void)viewDidLoad {
    [super viewDidLoad];

    NSURL *url = [NSURL URLWithString:(@"http://myURL/ios8.png")];
    NSData *data = [NSData dataWithContentsOfURL:url];

    _imageView.image = [UIImage imageWithData: data];
    _labelURL.text = @"http://www.quentinroussat.fr/assets/img/iOS%20icon's%20Style/ios8.png";
 }

有人可以解释一下为什么imageWithData:Swift无法使用它，以及如何解决该问题。

Answer 1

Xcode 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 code")
    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 code. 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")