如何等待 RequestAccessAsync？答案

【问题标题】：How to await for RequestAccessAsync?如何等待 RequestAccessAsync？
【发布时间】：2017-05-30 03:46:45
【问题描述】：

我正在尝试按照this example on Micr*soft's blog 上的步骤创建 Windows 通知的侦听器

据说获得用户授权的第二个代码片段没有编译：

error CS4033: The 'await' operator can only be used within an async method. 
Consider marking this method with the 'async' modifier and changing its return type to 'Task'.

虽然我不熟悉C#的async/await机制，但是问题的方法叫RequestAccessAsync，Visual Studio打开的源码在方法上方有一个[RemoteAsync]。

这是完整的代码片段：

// Get the listener
UserNotificationListener listener = UserNotificationListener.Current;

// And request access to the user's notifications (must be called from UI thread)
UserNotificationListenerAccessStatus accessStatus = await listener.RequestAccessAsync();

switch (accessStatus)
{
    // This means the user has granted access.
    case UserNotificationListenerAccessStatus.Allowed:

        // Yay! Proceed as normal
        break;

    // This means the user has denied access.
    // Any further calls to RequestAccessAsync will instantly
    // return Denied. The user must go to the Windows settings
    // and manually allow access.
    case UserNotificationListenerAccessStatus.Denied:

        // Show UI explaining that listener features will not
        // work until user allows access.
        break;

    // This means the user closed the prompt without
    // selecting either allow or deny. Further calls to
    // RequestAccessAsync will show the dialog again.
    case UserNotificationListenerAccessStatus.Unspecified:

        // Show UI that allows the user to bring up the prompt again
        break;
}

我该如何解决这个问题？

【问题讨论】：

你的方法签名在哪里？你把它标记为async了吗？
您需要展示更多代码，您需要展示保存您的代码示例的方法，
谢谢大家，这就是问题所在。这段代码在一个类构造函数中，（正如我刚刚学到的，不能是异步的）
@RSFalcon7 查看我更新的答案，以解决在构造函数中运行异步代码的解决方法。

标签： c# uwp async-await

【解决方案1】：

这不是完整的代码sn-p...你需要将调用方法标记为async。

public async Task<ReturnType> MyMethod()
{
    // Get the listener
    UserNotificationListener listener = UserNotificationListener.Current;

    // And request access to the user's notifications (must be called from UI thread)
    UserNotificationListenerAccessStatus accessStatus = await listener.RequestAccessAsync();
}

要在构造函数中执行此操作，根据您的 cmets，我会像这样使用 Nito.AsyncEx 和 AsyncContext：

public class MyProgram
{
    public MyProgram()
    {
        UserNotificationListenerAccessStatus accessStatus = AsyncContext.Run(listener.RequestAccessAsync);
    }
}

【讨论】：