在Swift上从URL加载/下载图像 [英] Loading/Downloading image from URL on Swift

问题描述

我想从我的应用程序中的URL加载一个图像，所以我首先尝试使用Objective-C，然而它可以使用Swift，我有一个编译错误：

I'd like to load an image from a URL in my application, so I first tried with Objective-C and it worked, however, with Swift, I've a compilation error:

'imageWithData'不可用：使用对象构造'UIImage（数据:)'

'imageWithData' is unavailable: use object construction '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：

In Objective-C:

- (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：不适用于Swift，我该如何解决问题。

Can someone please explain me why the imageWithData: doesn't work with Swift, and how can I solve the problem.

推荐答案

Xcode 8•Swift 3

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：

创建一个使用完成处理程序从您的网址获取图像数据的方法

func getData(from url: URL, completion: @escaping (Data?, URLResponse?, Error?) -> ()) {
    URLSession.shared.dataTask(with: url, completionHandler: completion).resume()
}

创建下载图像的方法（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() {
            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")
    if let url = URL(string: "http://www.apple.com/euro/ios/ios8/a/generic/images/og.png") {
        imageView.contentMode = .scaleAspectFit
        downloadImage(from: url)
    }
    print("End of code. The image will continue downloading in the background and it will be loaded when it ends.")
}

---

扩展程序：

extension UIImageView {
    func downloaded(from url: URL, contentMode mode: UIViewContentMode = .scaleAspectFit) {
        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() {
                self.image = image
            }
        }.resume()
    }
    func downloaded(from link: String, contentMode mode: UIViewContentMode = .scaleAspectFit) {
        guard let url = URL(string: link) else { return }
        downloaded(from: url, contentMode: mode)
    }
}

用法：

imageView.downloaded(from: "http://www.apple.com/euro/ios/ios8/a/generic/images/og.png")

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