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.

我建议使用Kingfisher库来异步下载图像。使用翠鸟最好的部分是，它默认缓存所有下载的图像，图像url作为id。下次当您请求下载具有特定URl的图像时，它将从缓存中加载它。

用法:

newsImage.kf.setImage(with: imageUrl!, placeholder: nil, options: nil, progressBlock: nil, completionHandler: { (image, error, cacheType, imageUrl) in
                if error == nil{
                    self.activityIndicator.stopAnimating()
                }else if error != nil{
                    self.activityIndicator.stopAnimating()
                }
            })

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
    }

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")

class Downloader {
    
    class func downloadImageWithURL(url: String) -> UIImage! {
        
        let date = NSData(contentsOf: URL(string: url)!)
        return UIImage(data: date! as Data)
    }
}

用法:

let img = Downloader.downloadImageWithURL(url: imageURL)
        self.imageView1.image = img