PROSAGA码农传奇-IOS-在Swift上从URL加载/下载图像

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
}
```

异步地：

创建带有完成处理程序的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()
}
```
创建一种下载图像的方法（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() { [weak self] in
            self?.imageView.image = UIImage(data: data)
        }
    }
}
```

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.")
}
```

扩展名：

```
extension UIImageView {
    func downloaded(from url: URL, contentMode mode: UIView.ContentMode = .scaleAspectFit) {
        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() { [weak self] in
                self?.image = image
            }
        }.resume()
    }
    func downloaded(from link: String, contentMode mode: UIView.ContentMode = .scaleAspectFit) { 
        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")`