URLSession dataTask completionHandler在游乐场中不起作用 [英] URLSession dataTask completionHandler does not work in playground

问题描述

我在youtube上观看了一个教程并尝试了这些教程。然后我在操场文件中写了
代码，但没有结果，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。在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内的所有工作。以下是XCode项目中的代码。

I watched a tutorial from youtube and tried that tutorials. Then I write the code in playground file and I got no result but there is no error. Thus I make a new Project in XCode. Then add a Button to Main.StoryBoard and connect the UI to code. After doing all necessary things I runthe project in simulator and everything go well and I can see all the work inside completion handler. Following is the code in XCode project.

@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()
}

以下是操场上的代码。

Following is the code in playground.

// 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()

推荐答案

您需要告诉操场继续执行足够长的时间以完成异步代码。为此：

You need to tell the playground to continue execution long enough for your async code to complete. To do that:

import PlaygroundSupport 

PlaygroundPage.current.needsIndefiniteExecution = true 

来自 Apple关于此属性的文档：

默认情况下，执行所有顶级代码，然后执行
终止。使用异步代码时，启用无限
执行以允许在
playground的顶级代码结束后继续执行。反过来，这给线程
和回调时间执行。

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.

这篇关于URLSession dataTask completionHandler在游乐场中不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！