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

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
    }

2017-04-30 09:17:09

其他回答

Xcode 12•Swift 5

Leo Dabus的答案非常棒!我只是想提供一个一体化的功能解决方案:

if 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()
}

2016-09-23 17:18:49

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)
                        })
                    }

2019-01-02 23:18:40

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

AsyncImage是在iOS 15之后正式引入的，一个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:

使用init(url:scale:content:placeholder:)指定一个自定义占位符。要获得对加载过程的更多控制，请使用init(url:scale:transaction:content:)

详见文档

2021-06-10 03:34:02

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

在Swift上从URL加载/下载图像

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