ios - URLSession dataTask completionHandler 在 Playground 上不起作用

Question

我从 youtube 上观看了一个教程并尝试了该教程。然后我写 Playground 文件中的代码，我没有得到任何结果，但没有错误。因此，我在 XCode 中创建了一个新项目。然后向 Main.StoryBoard 添加一个 Button 并将 UI 连接到代码。完成所有必要的事情后，我在模拟器中运行项目，一切顺利，我可以看到完成处理程序中的所有工作。以下是 XCode 项目中的代码。

@IBAction func doNetwork(_ sender: UIButton) {
    print("start network jobs...")
    // url
    let url: URL! = URL(string: "http://192.168.0.12/swnet.php")
    URLCache.shared = URLCache(memoryCapacity: 0, diskCapacity: 0, diskPath: nil)
    // url session
    let session = URLSession.shared
    let task: URLSessionDataTask = session.dataTask(with: url, completionHandler: {
        (data, response, error) in
        print("Handler")
        if let respData = data {
            print("Data")
            print(respData)
        }
        if let resp = response {
            print("Resp")
            print(resp)
        }
        if let err = error {
            print("Error")
            print(err)
        }

    })

    task.resume()
}

以下是 playground 中的代码。

// url
let url: URL! = URL(string: "http://192.168.0.12/swnet.php")
URLCache.shared = URLCache(memoryCapacity: 0, diskCapacity: 0, diskPath: nil)
// url session
let session = URLSession.shared
let task: URLSessionDataTask = session.dataTask(with: url, completionHandler: {
    (data, response, error) in
    print("Handler")
    if let respData = data {
        print("Data")
        print(respData)
    }
    if let resp = response {
        print("Resp")
        print(resp)
    }
    if let err = error {
        print("Error")
        print(err)
    }

})

task.resume()

Answer 1

您需要告诉 playground 继续执行足够长的时间以使您的异步代码完成。为此:

import PlaygroundSupport 

PlaygroundPage.current.needsIndefiniteExecution = true 

来自 Apple's docs on this property :

By default, all top-level code is executed, and then execution is terminated. When working with asynchronous code, enable indefinite execution to allow execution to continue after the end of the playground’s top-level code is reached. This, in turn, gives threads and callbacks time to execute.