在Swift上从URL加载/下载图像

我想从我的应用程序中的URL加载图像，所以我首先尝试了Objective-C和它的工作，但是，与Swift，我有一个编译错误:

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

我的函数:

@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";
 }

有人能解释一下为什么imageWithData:不能与Swift一起工作，我该如何解决这个问题。

当前回答

Swift 4.1我创建了一个函数，只是传递图像url，图像生成后缓存键设置为完成块。

   class NetworkManager: NSObject {
  
  private var imageQueue = OperationQueue()
  private var imageCache = NSCache<AnyObject, AnyObject>()
  
  func downloadImageWithUrl(imageUrl: String, cacheKey: String, completionBlock: @escaping (_ image: UIImage?)-> Void) {
    
    let downloadedImage = imageCache.object(forKey: cacheKey as AnyObject)
    if let  _ = downloadedImage as? UIImage {
      completionBlock(downloadedImage as? UIImage)
    } else {
      let blockOperation = BlockOperation()
      blockOperation.addExecutionBlock({
        let url = URL(string: imageUrl)
        do {
          let data = try Data(contentsOf: url!)
          let newImage = UIImage(data: data)
          if newImage != nil {
            self.imageCache.setObject(newImage!, forKey: cacheKey as AnyObject)
            self.runOnMainThread {
              completionBlock(newImage)
            }
          } else {
            completionBlock(nil)
          }
        } catch {
          completionBlock(nil)
        }
      })
      self.imageQueue.addOperation(blockOperation)
      blockOperation.completionBlock = {
        print("Image downloaded \(cacheKey)")
      }
    }
  }
}
extension NetworkManager {
  fileprivate func runOnMainThread(block:@escaping ()->Void) {
    if Thread.isMainThread {
      block()
    } else {
      let mainQueue = OperationQueue.main
      mainQueue.addOperation({
        block()
      })
    }
  }
}

2018-08-19 14:53:53

其他回答

对于Swift-3及以上版本:

extension UIImageView {
  public func imageFromUrl(urlString: String) {
    if let url = URL(string: urlString) {
        let request = URLRequest(url: url)
        NSURLConnection.sendAsynchronousRequest(request as URLRequest, queue: .main, completionHandler: { (response, data, error) in
            if let imageData = data as NSData? {
                self.image = UIImage(data: imageData as Data)
            }
        })
    }
  }
}

2017-06-15 11:24:46

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"))

2020-04-23 11:54:03

Swift 4.2和AlamofireImage

如果使用库不是问题，您可以通过AlamofireImage的帮助来完成。我的样本来自它的Github

占位符图片

let imageView = UIImageView(frame: frame)
let url = URL(string: "https://httpbin.org/image/png")!
let placeholderImage = UIImage(named: "placeholder")!
imageView.af_setImage(withURL: url, placeholderImage: placeholderImage)

它有许多方便的功能和扩展工作与图像。从缓存到缩放和调整大小，甚至在图像上应用过滤器。如果图像在你的应用中很重要，我建议使用这个框架来节省你的时间。

2019-01-09 21:15:21

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:)

2018-09-11 08:44:49

翠鸟是一个最好的库加载图像到URL。

Github URL - https://github.com/onevcat/Kingfisher

// If you want to use Activity Indicator.
imageview_pic.kf.indicatorType = .activity
imageview_pic.kf.setImage(with: URL(string: "Give your url string"))

// If you want to use custom placeholder image.
imageview_pic.kf.setImage(with: URL(string: "Give your url string"), placeholder: UIImage(named: "placeholder image name"), options: nil, progressBlock: nil, completionHandler: nil)

2018-04-13 21:13:06

在Swift上从URL加载/下载图像

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