Swift async/await关键字

在日常项目开发中，一般耗时的操作我们不可能全部让主线程去做完，会导致app的卡顿。我们一般都是异步执行的。

以图片渲染为例子。

闭包

从前我们经常是异步下载了图片，然后闭包为回调触发使用。

异步下载图片闭包回调

    private func blockGetImage(completionHandler: @escaping(Data) -> Void) {
        
        DispatchQueue.global().async {
            let url : URL = URL(string: "http://i8-static.jjwxc.net/tmp/backend/authorspace/s1/28/27087/2708639/20220518224228.jpg")!
            let data : Data = try! Data(contentsOf: url)
            DispatchQueue.main.async {
                completionHandler(data)
            }
        }
    }}

闭包使用

SwiftUI

    var body: some View {
        VStack
        {
            Image(uiImage: UIImage(data: data) ?? UIImage())
                .resizable()
        }
        .onAppear {
            print("name = \(self)")
            blockGetImage {
                data = $0
            }
        }
        .navigationTitle("async和await")
    }

Swift

    override func viewDidLoad() {
        super.viewDidLoad()
        self.img = UIImageView(frame: CGRect(x: 0, y: 100, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height - 100))
        self.view.addSubview(self.img)
        
        blockGetImage {
            self.img.image = UIImage(data: $0)
        }
        
   }

async/await

async是异步请求
await是将async异步转为同步

    // async方式得到图片的Data
    private func asyncGetImage() async -> Data {
        do {
            let (d, _) = try await URLSession.shared.data(for: URLRequest(url: URL(string: "http://i8-static.jjwxc.net/tmp/backend/authorspace/s1/28/27087/2708639/20220518224228.jpg")!))
            return d
        } catch {
            return Data()
        }
    }

SwiftUI使用

    var body: some View {
        VStack
        {
            Image(uiImage: UIImage(data: data) ?? UIImage())
                .resizable()
        }
        .onAppear {
            print("name = \(self)")
        }
        .task { 
            data = await asyncGetImage()
        }
        .navigationTitle("async和await")
    }

Swift使用

    override func viewDidLoad() {
        super.viewDidLoad()
        self.img = UIImageView(frame: CGRect(x: 0, y: 100, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height - 100))
        self.view.addSubview(self.img)
        
        Task {
            self.img.image = await UIImage(data: asyncGetImage())
        }
    }

Github地址

懒得打的可以直接打开项目查看 Github地址 https://github.com/HahnLoving/iOS_Study