swift - 用GCD下载图片并显示

DispatchQueue.global().async {
var image: UIImage?

let imageURL: URL = URL(string: "https://pic4.zhimg.com/v2-ae2d8b65d65eaf011d1ed873f504e1db_b.jpg")!

URLSession(configuration: .default)
.dataTask(with: imageURL, completionHandler: {
(imageData, response, error) in
if let data = imageData {
print("Did download image data")
//主线程里显示图片
DispatchQueue.main.async {
image = UIImage(data: data)
let imageView = UIImageView(image: image)
imageView.contentMode = .scaleAspectFit
self.view.addSubview(imageView)
}
}
}).resume()
}

更多在swift3.0里使用GCD 参考这篇博客