c# - WinRT 对象中的异步回调应该如何实现？

Question

到目前为止，我可以创建一个委托类型，例如：

// Can't use Task in WinRT interface and TypedEventHandler doesn't work with async await
public delegate IAsyncOperation<string> AsyncEventHandler(object sender, object args);

然后像这样在 WinRT 对象中公开：

public AsyncEventHandler OnMyEvent { get; set; }

在 WinRT 对象中，我会这样称呼它：

if (OnMyEvent != null)
{
    var result = await OnMyEvent.Invoke(this, someArgs);
    // Do something with the result...
}

使用 WinRT 对象的客户端代码可以执行以下操作：

instanceOfWinRTObject.OnMyEvent = OnCalledBackFromWinRT;

但是因为委托返回 anIAsyncOperation我们需要做一些包装：

private async Task<string> OnCalledBackFromWinRTAsync(object sender,
        object args)
{
    return await GetSomeStringAsync(args);
}

private IAsyncOperation<string> OnCalledBackFromWinRT(object sender, object args)
{
    return OnCalledBackFromWinRTAsync(sender, args).AsAsyncOperation();
}

只是感觉必须有一种更清洁的方法来实现这一目标。

Answer 1

这是 Peter Torr 的评论提示的另一种选择。

// Custom event args class
public sealed class MyEventArgs
{
    public string Result;
    public Deferral Deferral;
}

// Declare the event handler on the WinRT component
public event TypedEventHandler<object, MyEventArgs> OnSuspendingEvent;

然后在 WinRT 组件中，您可以像这样调用事件：

if (OnSuspendingEvent != null)
{
    var tcs = new TaskCompletionSource();
    using (var deferral = new Deferral(() => tcs.SetResult(true)))
    {
        var myArgs = MyEventArgs();
        myArgs.Deferral = deferral;
        OnSuspendUnloading.Invoke(this, myArgs);
        await tcs.Task;
        DoSomethingWithResult(args.Result);
    }
}

最后在客户端代码中添加一个处理程序，如下所示：

instanceOfWinRTObject.OnSuspendingEvent += async (sender, args) =>
{
    var deferral = args.Deferral;
    try
    {
        // Client does some async work with a result
        args.Result = await GetSomeStringAsync(args);
    }
    finally
    {
        deferral.Complete();
    }
}