如果你只是想加载图像(异步!)-只需添加这个小扩展到你的swift代码:

extension UIImageView {
    public func imageFromUrl(urlString: String) {
        if let url = NSURL(string: urlString) {
            let request = NSURLRequest(URL: url)
            NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) {
                (response: NSURLResponse?, data: NSData?, error: NSError?) -> Void in
                if let imageData = data as NSData? {
                    self.image = UIImage(data: imageData)
                }
            }
        }
    }
}

然后这样用:

myImageView.imageFromUrl("https://robohash.org/123.png")

一种获取图像的方法是安全的，适用于Swift 2.0和X-Code 7.1:

static func imageForImageURLString(imageURLString: String, completion: (image: UIImage?, success: Bool) -> Void) {
    guard let url = NSURL(string: imageURLString),
        let data = NSData(contentsOfURL: url),
        let image = UIImage(data: data)
        else { 
            completion(image: nil, success: false); 
            return 
       }

    completion(image: image, success: true)
}

然后你可以像这样调用这个方法:

imageForImageURLString(imageString) { (image, success) -> Void in
        if success {
            guard let image = image 
                 else { return } // Error handling here 
            // You now have the image. 
         } else {
            // Error handling here.
        }
    }

如果你要用图像更新视图，你必须在" If success{"后面加上这个:

    dispatch_async(dispatch_get_main_queue()) { () -> Void in
         guard let image = image 
              else { return } // Error handling here 
         // You now have the image. Use the image to update the view or anything UI related here
         // Reload the view, so the image appears
    }

The reason this last part is needed if you are using the image in the UI is because network calls take time. If you try to update the UI using the image without calling dispatch_async like above, the computer will look for the image while the image is still being fetched, find that there is no image (yet), and move on as if there was no image found. Putting your code inside of a dispatch_async completion closure says to the computer, "Go, get this image and when you are done, then complete this code." That way, you will have the image when the code is called and things will work well.

Swift 2.0:

1)

if let url = NSURL(string: "http://etc...") {
    if let data = NSData(contentsOfURL: url) {
        imageURL.image = UIImage(data: data)
    }        
}

OR

imageURL.image =
    NSURL(string: "http:// image name...")
    .flatMap { NSData(contentsOfURL: $0) }
    .flatMap { UIImage(data: $0) }

2)将此方法添加到VC或Extension中。

func load_image(urlString:String)
{   let imgURL: NSURL = NSURL(string: urlString)!
    let request: NSURLRequest = NSURLRequest(URL: imgURL)

    NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) { (response: NSURLResponse?, data: NSData?, error: NSError?) in

        if error == nil {
            self.image_element.image = UIImage(data: data)
        }
    }
}

用法:

self.load_image(" url strig here")

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)

斯威夫特4

这个方法将从一个网站异步下载图像并缓存它:

    func getImageFromWeb(_ urlString: String, closure: @escaping (UIImage?) -> ()) {
        guard let url = URL(string: urlString) else {
return closure(nil)
        }
        let task = URLSession(configuration: .default).dataTask(with: url) { (data, response, error) in
            guard error == nil else {
                print("error: \(String(describing: error))")
                return closure(nil)
            }
            guard response != nil else {
                print("no response")
                return closure(nil)
            }
            guard data != nil else {
                print("no data")
                return closure(nil)
            }
            DispatchQueue.main.async {
                closure(UIImage(data: data!))
            }
        }; task.resume()
    }

在使用:

    getImageFromWeb("http://www.apple.com/euro/ios/ios8/a/generic/images/og.png") { (image) in
        if let image = image {
            let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
            imageView.image = image
            self.view.addSubview(imageView)
        } // if you use an Else statement, it will be in background
    }

Swift 4:一个简单的小图像加载器(例如:缩略图)，使用NSCache，总是运行在主线程上:

class ImageLoader {

  private static let cache = NSCache<NSString, NSData>()

  class func image(for url: URL, completionHandler: @escaping(_ image: UIImage?) -> ()) {

    DispatchQueue.global(qos: DispatchQoS.QoSClass.background).async {

      if let data = self.cache.object(forKey: url.absoluteString as NSString) {
        DispatchQueue.main.async { completionHandler(UIImage(data: data as Data)) }
        return
      }

      guard let data = NSData(contentsOf: url) else {
        DispatchQueue.main.async { completionHandler(nil) }
        return
      }

      self.cache.setObject(data, forKey: url.absoluteString as NSString)
      DispatchQueue.main.async { completionHandler(UIImage(data: data as Data)) }
    }
  }

}

用法:

ImageLoader.image(for: imageURL) { image in
  self.imageView.image = image
}