在Swift上从URL加载/下载图像

时间：2014-06-15 16:27:05

标签： ios swift uiimage nsurl

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然后使用Swift，我有一个编译错误：

  

'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imageWithData:为何与Swift不兼容，以及如何解决问题。

34 个答案:

答案 0 :(得分：691)

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：

使用完成处理程序创建一个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)
        }
    }
}

<强>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.")
}

<强>扩展：

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() {
                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")

答案 1 :(得分：306)

（Swift 4更新） 要直接回答原始问题，这里是发布的Objective-C片段的快速等价物。

let url = URL(string: image.url)
let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
imageView.image = UIImage(data: data!)

<强>声明：

请务必注意，Data(contentsOf:)方法会在执行代码的同一个帖子中下载网址同步的内容，因此不要在应用程序的主线程中调用它。

使用GCD实现异步运行相同代码而不是阻止UI的简单方法是：

let url = URL(string: image.url)

DispatchQueue.global().async {
    let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
    DispatchQueue.main.async {
        imageView.image = UIImage(data: data!)
    }
}

也就是说，在现实生活中的应用程序中，如果您希望获得最佳用户体验并避免多次下载同一图像，您可能还希望它们不仅可以下载，还可以缓存。已经有相当多的库可以非常无缝地完成，它们都非常易于使用。我个人推荐Kingfisher：

import Kingfisher

let url = URL(string: "url_of_your_image")
// this downloads the image asynchronously if it's not cached yet
imageView.kf.setImage(with: url)

就是这样

答案 2 :(得分：63)

如果您只想加载图片（异步！） - 只需将此小扩展名添加到您的swift代码中：

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)
                }
            }
        }
    }
}

并以这种方式使用它：

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

答案 3 :(得分：42)

Swift 2.2 || Xcode 7.3

  

我得到了惊人的结果 !!使用 AlamofireImage swift库

它提供了多种功能，如：

  • 异步 下载
  • 如果应用程序发生内存警告，则自动清除图像缓存
  • 图片网址缓存
  • 图片缓存
  • 避免重复下载

并且很容易为您的应用实施

Step.1安装窗格

Alamofire 3.3.x

  

pod＆＃39; Alamofire＆＃39;

AlamofireImage 2.4.x

  

pod＆＃39; AlamofireImage＆＃39;

Step.2导入和使用

import Alamofire
import AlamofireImage

let downloadURL = NSURL(string: "http://cdn.sstatic.net/Sites/stackoverflow/company/Img/photos/big/6.jpg?v=f4b7c5fee820")!
imageView.af_setImageWithURL(downloadURL)

那是它！它将照顾一切

非常感谢Alamofire guys，让iDevelopers变得轻松生活;）

答案 4 :(得分：25)

Xcode 8 • Swift 3

Leo Dabus的答案太棒了！我只是想提供一体化的功能解决方案：

let url = URL(string: 
    "http://www.apple.com/euro/ios/ios8/a/generic/images/og.png")

let task = URLSession.shared.dataTask(with: url!) { data, response, error in
    guard let data = data, error == nil else { return }

    DispatchQueue.main.async() {    // execute on main thread
        self.imageView.image = UIImage(data: data)
    }
}

task.resume()

答案 5 :(得分：16)

我将问题的最佳答案代码包装到一个扩展UIImageView的单个可重用类中，这样您就可以直接在故事板中使用异步加载UIImageViews（或者从代码中创建它们）。

这是我的班级：

import Foundation
import UIKit

class UIImageViewAsync :UIImageView
{

    override init()
    {
        super.init(frame: CGRect())
    }

    override init(frame:CGRect)
    {
        super.init(frame:frame)
    }

    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    func getDataFromUrl(url:String, completion: ((data: NSData?) -> Void)) {
        NSURLSession.sharedSession().dataTaskWithURL(NSURL(string: url)!) { (data, response, error) in
            completion(data: NSData(data: data))
        }.resume()
    }

    func downloadImage(url:String){
        getDataFromUrl(url) { data in
            dispatch_async(dispatch_get_main_queue()) {
                self.contentMode = UIViewContentMode.ScaleAspectFill
                self.image = UIImage(data: data!)
            }
        }
    }
}

以下是如何使用它：

imageView.downloadImage("http://www.image-server.com/myImage.jpg")

答案 6 :(得分：13)

let url = NSURL.URLWithString("http://live-wallpaper.net/iphone/img/app/i/p/iphone-4s-wallpapers-mobile-backgrounds-dark_2466f886de3472ef1fa968033f1da3e1_raw_1087fae1932cec8837695934b7eb1250_raw.jpg");
var err: NSError?
var imageData :NSData = NSData.dataWithContentsOfURL(url,options: NSDataReadingOptions.DataReadingMappedIfSafe, error: &err)
var bgImage = UIImage(data:imageData)

答案 7 :(得分：13)

仅供参考：对于swift-2.0 Xcode7.0 beta2 

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
                self.image = UIImage(data: data!)
            }
        }
    }
}

答案 8 :(得分：8)

swift 3，错误处理

let url = URL(string: arr[indexPath.row] as! String)
if url != nil {
    DispatchQueue.global().async {
        let data = try? Data(contentsOf: url!) //make sure your image in this url does exist, otherwise unwrap in a if let check / try-catch
        DispatchQueue.main.async {
            if data != nil {
                cell.imgView.image = UIImage(data:data!)
            }else{
                cell.imgView.image = UIImage(named: "default.png")
            }
        }
    }
}

使用扩展程序

extension UIImageView {

    func setCustomImage(_ imgURLString: String?) {
        guard let imageURLString = imgURLString else {
            self.image = UIImage(named: "default.png")
            return
        }
        DispatchQueue.global().async {
            let data = try? Data(contentsOf: URL(string: imageURLString)!)
            DispatchQueue.main.async {
                self.image = data != nil ? UIImage(data: data!) : UIImage(named: "default.png")
            }
        }
    }
}

扩展使用

myImageView。 setCustomImage（ “URL”）

答案 9 :(得分：7)

Swift 4：一个简单的小图片加载器（例如：缩略图），它使用NSCache并始终在主线程上运行：

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
}

答案 10 :(得分：7)

你想做的事：

UIImage(data: data)

在Swift中，他们用常规构造函数替换了大多数Objective C工厂方法。

请参阅：

https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/InteractingWithObjective-CAPIs.html#//apple_ref/doc/uid/TP40014216-CH4-XID_26

答案 11 :(得分：7)

Swift 2，错误处理和自定义请求标题

只需向UIImageView添加扩展名：

extension UIImageView {
    public func imageFromUrl(urlString: String) {
        if let url = NSURL(string: urlString) {
            let request = NSMutableURLRequest(URL: url)
            request.setValue("<YOUR_HEADER_VALUE>", forHTTPHeaderField: "<YOUR_HEADER_KEY>")
            NSURLSession.sharedSession().dataTaskWithRequest(request) {
                (data, response, error) in
                guard let data = data where error == nil else{
                    NSLog("Image download error: \(error)")
                    return
                }

                if let httpResponse = response as? NSHTTPURLResponse{
                    if httpResponse.statusCode > 400 {
                        let errorMsg = NSString(data: data, encoding: NSUTF8StringEncoding)
                        NSLog("Image download error, statusCode: \(httpResponse.statusCode), error: \(errorMsg!)")
                        return
                    }
                }

            dispatch_async(dispatch_get_main_queue(), {
                NSLog("Image download success")
                self.image = UIImage(data: data)
            })
            }.resume()
        }
    }
}

然后，使用新的imageFromUrl(urlString: String)下载图片

<强>用法： 

imageView.imageFromUrl("https://i.imgur.com/ONaprQV.png")

答案 12 :(得分：6)

Swift 4

此方法将异步下载网站中的图像并将其缓存：

    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()
    }

使用中：

    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
    }

答案 13 :(得分：5)

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。

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")

答案 14 :(得分：4)

  

Kingfisher是将图片加载到网址的最佳图书馆之一。

Github网址 - 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)

答案 15 :(得分：3)

如果您正在寻找一个非常简单的实现。 （这在Swift 2中对我有用）

 let imageURL = NSURL(string: "https://farm2.staticflickr.com/1591/26078338233_d1466b7da2_m.jpg")
 let imagedData = NSData(contentsOfURL: imageURL!)!
 imageView?.image = UIImage(data: imagedData)

我在一个tableview中实现了一个只有图像的自定义单元格

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell{

        let cell = tableView.dequeueReusableCellWithIdentifier("theCell", forIndexPath: indexPath) as! customTableViewCell

        let imageURL = NSURL(string: "https://farm2.staticflickr.com/1591/26078338233_d1466b7da2_m.jpg")

        let imagedData = NSData(contentsOfURL: imageURL!)!

        cell.imageView?.image = UIImage(data: imagedData)

        return cell

    }

答案 16 :(得分：3)

获取安全图像并使用Swift 2.0和X-Code 7.1的方法：

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)
}

然后你会这样调用这个方法：

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.
        }
    }

如果您要使用图片更新视图，则必须在＆＃34之后使用此视图;如果成功{＆＃34;：

    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
    }

如果在UI中使用图像，则需要最后一部分是因为网络调用需要时间。如果您尝试使用图像更新UI而不像上面那样调用dispatch_async，计算机将在图像仍然被提取时查找图像，发现没有图像（尚未），并继续前进，就像没有图像一样找到。将代码放入dispatch_async完成闭包中对计算机说，＆＃34; Go，获取此图像，完成后再完成此代码。＆＃34;这样，您将在调用代码时获得图像，并且事情会很好。

答案 17 :(得分：3)

您可以使用pod SDWebImage来实现相同目的。它易于使用。您可以在这里SDWebImage

这是示例代码

self.yourImage.sd_setImage(with: NSURL(string: StrUrl as String ) as URL!, placeholderImage: placeholderImage, options: SDWebImageOptions(rawValue: 0), completed: { (image, error, cacheType, imageURL) in
                if( error != nil)
                {
                    print("Error while displaying image" , (error?.localizedDescription)! as String)
                }
            })

答案 18 :(得分：3)

我建议使用Kingfisher库异步下载图像。关于使用Kingfisher最好的部分是，默认情况下，它以图像URL作为ID缓存所有下载的图像。下次当您请求下载带有该特定URl的图像时，它将从缓存中加载。

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()
                }
            })

答案 19 :(得分：1)

将图像下载到文件的Swift 2.x答案（与Leo Dabus的答案相反，后者将图像存储在内存中）。基于Leo Dabus的答案和Rob在Get the data from NSURLSession DownloadTaskWithRequest from completion handler的回答：

    // Set download vars
    let downloadURL = NSURL() // URL to download from
    let localFilename = "foobar.png" // Filename for storing locally 

    // Create download request
    let task = NSURLSession.sharedSession().downloadTaskWithURL(downloadURL) { location, response, error in
        guard location != nil && error == nil else {
            print("Error downloading message: \(error)")
            return
        }

        // If here, no errors so save message to permanent location
        let fileManager = NSFileManager.defaultManager()
        do {
            let documents = try fileManager.URLForDirectory(.DocumentDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: false)
            let fileURL = documents.URLByAppendingPathComponent(localFilename)
            try fileManager.moveItemAtURL(location!, toURL: fileURL)
            self.doFileDownloaded(fileURL, localFilename: localFilename)
            print("Downloaded message @ \(localFilename)")
        } catch {
            print("Error downloading message: \(error)")
        }
    }

    // Start download
    print("Starting download @ \(downloadURL)")
    task.resume()


// Helper function called after file successfully downloaded
private func doFileDownloaded(fileURL: NSURL, localFilename: String) {

    // Do stuff with downloaded image

}

答案 20 :(得分：1)

class ImageStore: NSObject { 
    static let imageCache = NSCache<NSString, UIImage>()
}

extension UIImageView {
    func url(_ url: String?) {
        DispatchQueue.global().async { [weak self] in
            guard let stringURL = url, let url = URL(string: stringURL) else {
                return
            }
            func setImage(image:UIImage?) {
                DispatchQueue.main.async {
                    self?.image = image
                }
            }
            let urlToString = url.absoluteString as NSString
            if let cachedImage = ImageStore.imageCache.object(forKey: urlToString) {
                setImage(image: cachedImage)
            } else if let data = try? Data(contentsOf: url), let image = UIImage(data: data) {
                DispatchQueue.main.async {
                    ImageStore.imageCache.setObject(image, forKey: urlToString)
                    setImage(image: image)
                }
            }else {
                setImage(image: nil)
            }
        }
    }
}

用法：

let imageView = UIImageView()
imageView.url("image url")

答案 21 :(得分：1)

Employee

我在UserAccountId类中创建了一个简单的类函数，用于调用您可以通过class func downloadImageFromUrl(with urlStr: String, andCompletionHandler:@escaping (_ result:Bool) -> Void) { guard let url = URL(string: urlStr) else { andCompletionHandler(false) return } DispatchQueue.global(qos: .background).async { URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) -> Void in if error == nil { let httpURLResponse = response as? HTTPURLResponse Utils.print( "status code ID : \(String(describing: httpURLResponse?.statusCode))") if httpURLResponse?.statusCode == 200 { if let data = data { if let image = UIImage(data: data) { ImageCaching.sharedInterface().setImage(image, withID: url.absoluteString as NSString) DispatchQueue.main.async { andCompletionHandler(true) } }else { andCompletionHandler(false) } }else { andCompletionHandler(false) } }else { andCompletionHandler(false) } }else { andCompletionHandler(false) } }).resume() } } 进行简单访问的方法，并使用Utils.swift类将图像保存在NSCache中

classname.methodname

快乐填充。干杯：）

答案 22 :(得分：1)

Swift 4.1，我创建了一个仅传递图像url的函数，在生成图像后将其设置为完成块。

sendBroadcast

答案 23 :(得分：1)

此处是用于从URL加载/下载图像的工作代码。在下载并加载实际映像（Swift 4代码）之前，NSCache自动并显示占位符映像。 

func NKPlaceholderImage(image:UIImage?, imageView:UIImageView?,imgUrl:String,compate:@escaping (UIImage?) -> Void){

    if image != nil && imageView != nil {
        imageView!.image = image!
    }

    var urlcatch = imgUrl.replacingOccurrences(of: "/", with: "#")
    let documentpath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
    urlcatch = documentpath + "/" + "\(urlcatch)"

    let image = UIImage(contentsOfFile:urlcatch)
    if image != nil && imageView != nil
    {
        imageView!.image = image!
        compate(image)

    }else{

        if let url = URL(string: imgUrl){

            DispatchQueue.global(qos: .background).async {
                () -> Void in
                let imgdata = NSData(contentsOf: url)
                DispatchQueue.main.async {
                    () -> Void in
                    imgdata?.write(toFile: urlcatch, atomically: true)
                    let image = UIImage(contentsOfFile:urlcatch)
                    compate(image)
                    if image != nil  {
                        if imageView != nil  {
                            imageView!.image = image!
                        }
                    }
                }
            }
        }
    }
}

像这样使用： 

// Here imgPicture = your imageView
// UIImage(named: "placeholder") is Display image brfore download and load actual image. 

NKPlaceholderImage(image: UIImage(named: "placeholder"), imageView: imgPicture, imgUrl: "Put Here your server image Url Sting") { (image) in }

答案 24 :(得分：1)

唯一缺少的是！

let url = NSURL.URLWithString("http://live-wallpaper.net/iphone/img/app/i/p/iphone-4s-wallpapers-mobile-backgrounds-dark_2466f886de3472ef1fa968033f1da3e1_raw_1087fae1932cec8837695934b7eb1250_raw.jpg");
var err: NSError?
var imageData :NSData = NSData.dataWithContentsOfURL(url!,options: NSDataReadingOptions.DataReadingMappedIfSafe, error: &err)
var bgImage = UIImage(data:imageData!)

答案 25 :(得分：0)

使用Ascyimageview，您可以轻松在imageview中加载imageurl。

让image1Url：URL = URL（字符串：“（imageurl）”作为字符串）！ imageview.imageURL = image1Url

答案 26 :(得分：0)

从服务器加载图像：- 

func downloadImage(from url: URL , success:@escaping((_ image:UIImage)->()),failure:@escaping ((_ msg:String)->())){
    print("Download Started")
    getData(from: url) { data, response, error in
        guard let data = data, error == nil else {
            failure("Image cant download from G+ or fb server")
            return
        }

        print(response?.suggestedFilename ?? url.lastPathComponent)
        print("Download Finished")
        DispatchQueue.main.async() {
             if let _img = UIImage(data: data){
                  success(_img)
            }
        }
    }
}
func getData(from url: URL, completion: @escaping (Data?, URLResponse?, Error?) -> ()) {
    URLSession.shared.dataTask(with: url, completionHandler: completion).resume()
}

用法：- 

  if let url = URL(string: "http://www.apple.com/euro/ios/ios8/a/generic/images/og.png") {
                        self.downloadImage(from:url , success: { (image) in
                            print(image)

                        }, failure: { (failureReason) in
                            print(failureReason)
                        })
                    }

答案 27 :(得分：0)

Swift 4.2和AlamofireImage

如果使用库不是问题，则可以在AlamofireImage的帮助下完成。 我的样本来自其Github

占位符图像示例： 

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)

它具有许多方便的功能和扩展功能，可以处理图像。从缓存到缩放和调整大小，甚至在图像上应用滤镜。如果图片对您的应用很重要，建议您使用此框架并节省时间。

答案 28 :(得分：0)

迅速5 

extension UIImageView {
    func load(url: URL) {
        DispatchQueue.global().async { [weak self] in
            if let data = try? Data(contentsOf: url) {
                if let image = UIImage(data: data) {
                    DispatchQueue.main.async {
                        self?.image = image
                    }
                }
            }
        }
    }
}

使用

override func awakeFromNib() {
    super.awakeFromNib()
    imgView.load(url: "<imageURLHere>")
}

答案 29 :(得分：0)

要在UITableView或UICollectionView中获得更好的性能，请使用轻量级库Smart Lazy Loading。如果要从异步url加载图像，可以使用这种惰性加载方法

在iOS中使用UICollectionView和UITableView在NSOperation或NSOperationQueue中进行智能“延迟加载”，因此在此项目中，我们可以在任何视图中下载多个图像（{{ 1}}或UICollectionView），通过使用UITableView和Operation并发来优化应用程序的性能。以下是该项目的关键点：智能延迟加载：创建图像下载服务。根据单元的可见性优先下载。

ImageDownloadService类将创建一个单例实例，并具有 NSCache 实例来缓存已下载的图像。我们已经将Operation类继承到TOperation以根据需要调整功能。我认为操作子类的属性在功能方面非常清楚。我们正在使用KVO监视操作状态的变化。

答案 30 :(得分：0)

使用SwiftUI时，SDWebImageSwiftUI是最佳选择。

通过XCode的Swift软件包管理器添加依赖项：https://github.com/SDWebImage/SDWebImageSwiftUI.git

然后只使用WebImage()而不是Image() 

WebImage(url: URL(string: "https://nokiatech.github.io/heif/content/images/ski_jump_1440x960.heic"))

答案 31 :(得分：0)

AsyncImage 是在 iOS 15 之后正式引入的，一种同步加载和显示图像的视图。

 var imageView : AsyncImage

imageView = AsyncImage(url: URL(string: entry.photo))
    .frame(width: 200, height: 200)

它还支持：

在doc中查看更多

答案 32 :(得分：-1)

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)
            }
        })
    }
  }
}

答案 33 :(得分：-1)

在Swift中使用此代码 

imageView.image=UIImage(data: NSData(contentsOfURL: NSURL(string: "http://myURL/ios8.png")!)!
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