Question

任意加载= YES，并检查功能中的后台提取。我究竟做错了什么？是否有解释这些概念的在线课程？这是在app委托文件中。我想在应用程序进入后台时从URL检索数据。

func applicationDidEnterBackground(_ application: UIApplication) {

    if let url = URL(string:"https://finviz.com/screener.ashx?v=111&f=exch_nasd,sh_curvol_o500,sh_price_u5&o=-change") {
        //url successful
        let task = URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
            if error != nil {
                //failed
                print("FAILED")
            } else {
                //successful
                print("SUCCESSFUL")
            }
        })
        print("TASK DID NOT RUN")
        task.resume()
    } else {
        //url failed
        print("URL FAILED")
    }
}

Answer 1

在运行代码之前使用beginBackgroundTask(expirationHandler:)。看看here。进入后台时系统会停止执行您的应用程序，您应该使用此功能以获得更多运行时间。同时删除＆＃34; TASK DID NOT RUN＆＃34;。它将始终打印

这是您的完整代码：

var identifier: UIBackgroundTaskIdentifier = 0

func applicationDidEnterBackground(_ application: UIApplication) {

self.identifier = application.beginBackgroundTask {
  application.endBackgroundTask(self.identifier)
}

if let url = URL(string:"https://finviz.com/screener.ashx?v=111&f=exch_nasd,sh_curvol_o500,sh_price_u5&o=-change") {
    //url successful
    let task = URLSession.shared.dataTask(with: url, completionHandler: { (data, response, error) in
        if error != nil {
            //failed
            print("FAILED")
        } else {
            //successful
            print("SUCCESSFUL")
        }
    })

    task.resume()
} else {
    //url failed
    print("URL FAILED")
}
}

在后台获取HTTP数据不起作用

1 个答案: