Xamarin.Ios BeingBackgroundTask参数

Question

我正在尝试 Xamarin 的这段代码。 Ios 后台任务文档：https://docs.microsoft.com/en-us/xamarin/ios/app-fundamentals/backgrounding/ios-backgrounding-techniques/ios-backgrounding-with-tasks。它说 行 6 中的变量 taskId 有 CS0841: Cannot use local variable 'taskId' before it is declared。我应该如何分配 taskId？另外，如何声明myFlag？我找不到有关如何使用此变量的任何说明。

Task.Factory.StartNew( () => {

    //expirationHandler only called if background time allowed exceeded
    var taskId = UIApplication.SharedApplication.BeginBackgroundTask(() => {
        Console.WriteLine("Exhausted time");
        UIApplication.SharedApplication.EndBackgroundTask(taskId); 
    });
    while(myFlag == true)
    {
        Console.WriteLine(UIApplication.SharedApplication.BackgroundTimeRemaining);
        myFlag = SomeCalculationNeedsMoreTime();
    }
    //Only called if loop terminated due to myFlag and not the expiration of time
    UIApplication.SharedApplication.EndBackgroundTask(taskId);
});

Answer 1

这是正确的 link : iOS Backgrounding with Tasks .

How should I assign the taskId?

正如link中提到的，taskId是注册过程中returns的唯一标识符，我们只需要在调用EndBackgroundTask时传递它即可。

nint taskID = UIApplication.SharedApplication.BeginBackgroundTask( () => {});
UIApplication.SharedApplication.EndBackgroundTask(taskId);

how do you declare myFlag?

这个变量只是表示后台任务结束的标志，如果你不想停止任务就设置为true。

Xamarin.Ios BeingBackgroundTask参数

Xamarin.Ios BeingBackgroundTask parameters

xamarin.ios

ios

xamarin

xamarin.forms