UWP AppServiceConnection - SendResponseAsync 返回 AppServiceResponseStatus.Failure

Question

我正在尝试在 Raspberry Pi3 上创建一个 UWP 服务应用程序，它提供对板载 UART 的访问。我遇到了有关 AppConnection 请求/响应的问题。

这是处理来自客户端应用程序的传入请求的服务方法

internal class Inbound
{
    public static async void OnRequestReceived(AppServiceConnection sender, AppServiceRequestReceivedEventArgs args)
    {
        var messageDeferral = args.GetDeferral();
        var response = new ValueSet();

        bool success = false;
        var msg = args.Request.Message.Keys;
        if (args.Request.Message.TryGetValue(ServiceApiRequests.Keys.Command, out object command))
        {
            try
            {
                switch (command)
                {

                    case ServiceApiRequests.CommandValues.UartWrite:
                        if (args.Request.Message.TryGetValue(ServiceApiRequests.Keys.UartTxBuffer, out object txBuffer))
                        {
                            string rxBuff = "";
                            success = await Pi3.Peripherals.Uart.GerInstance(57600).Write((string)txBuffer);

                            if (success)
                            {
                                Debug.WriteLine("Tx: " + (string)txBuffer);
                                if (args.Request.Message.TryGetValue(ServiceApiRequests.Keys.ReadUartResponse, out object getResponse))
                                {
                                    if ((string)getResponse == ServiceApiRequests.ReadUartResponse.Yes)
                                    {
                                        rxBuff = await Pi3.Peripherals.Uart.GerInstance(57600).Read();
                                        Debug.WriteLine("Rx: " + rxBuff);
                                    }
                                }
                            }
                            response.Add(ServiceApiRequests.Keys.UartRxBuffer, rxBuff);

                        }
                        break;
                }
            }
            catch (Exception ex)
            {
                success = false;
            }
        }

        response.Add(new KeyValuePair<string, object>(ServiceApiRequests.Keys.Result, success ? ServiceApiRequests.ResultValues.Ok : ServiceApiRequests.ResultValues.Ko));
        var result = await args.Request.SendResponseAsync(response);
        if (result == AppServiceResponseStatus.Failure)
        {
            Debug.WriteLine("Failed to send the response");
        }
        messageDeferral.Complete();
    }
}

如您所见，Uart 类是使用方法Pi3.Peripherals.Uart.GerInstance(57600) 使用单例模式获取的。

按照我用于从客户端应用程序发送请求的代码。

    public static class Uart
{
    public static IAsyncOperation<string> SendCommand(this AppServiceConnection DriverControllerConnection, string txBuffer, string awaitResponse = ServiceApiRequests.ReadUartResponse.Yes)
    {
        return _SendCommand(DriverControllerConnection, txBuffer, awaitResponse).AsAsyncOperation();
    }
    private static async Task<string> _SendCommand(AppServiceConnection DriverControllerConnection, string txBuffer, string awaitResponse)
    {
        AppServiceResponse response = null;
        string response_str = "";
        try
        {
            if (DriverControllerConnection != null)
            {
                response = await DriverControllerConnection.SendMessageAsync(new ServiceApiRequests.UartWrite().GetCommand(txBuffer, awaitResponse));
                if (response.Status == AppServiceResponseStatus.Success)
                {
                    if (response.Message.TryGetValue(ServiceApiRequests.Keys.Result, out object result))
                    {
                        if ((string)result == ServiceApiRequests.ResultValues.Ok && awaitResponse == ServiceApiRequests.ReadUartResponse.Yes)
                        {
                            response_str = response.Message[ServiceApiRequests.Keys.UartRxBuffer] as string;
                        }
                    }
                }
            }
        }
        catch (Exception ex)
        {
            // TODO: log
        }
        return response_str;
    }
}

系统运行良好一段时间，直到我有response.Status == AppServiceResponseStatus.Success，然后请求的结果发生变化，它变成AppServiceResponseStatus.Failure。这样程序计数器就不会进入条件if (response.Status == AppServiceResponseStatus.Success)。

知道原因吗？ 非常感谢您的帮助。

编辑

按照建议，我为ServiceClosed 事件添加了一个处理程序。这是主类。

public sealed class DriverListener : IBackgroundTask
{
    private BackgroundTaskDeferral backgroundTaskDeferral;
    private AppServiceConnection appServiceConnection;
    public void Run(IBackgroundTaskInstance taskInstance)
    {
        backgroundTaskDeferral = taskInstance.GetDeferral();
        // taskInstance.Canceled += OnTaskCanceled;

        var triggerDetails = taskInstance.TriggerDetails as AppServiceTriggerDetails;
        appServiceConnection = triggerDetails.AppServiceConnection;
        appServiceConnection.RequestReceived += Inbound.OnRequestReceived;
        appServiceConnection.ServiceClosed += OnTaskCanceled;
    }

    private void OnTaskCanceled(AppServiceConnection sender, AppServiceClosedEventArgs reason)
    {
        if (this.backgroundTaskDeferral != null)
        {
            Debug.WriteLine("ServiceClosed");
            // Complete the service deferral.
            this.backgroundTaskDeferral.Complete();
        }
    }
}

在这个函数中放置一个断点，我发现它从未被触发。 应用程序连接使用单例模式打开，并放入我在客户端应用程序中使用的 dll 中

    public static AppServiceConnection GetDriverConnectionInstance()
    {
        if (_DriverConnectionInstance == null)
        {
            try
            {
                _DriverConnectionInstance = OpenDriverConnection().AsTask().GetAwaiter().GetResult();
            }
            catch
            {

            }
        }
        return _DriverConnectionInstance;   
    }

我还向服务添加了一个切换 LED 的请求，我注意到 LED 状态发生了变化，但来自应用服务的响应仍然是“失败”并且消息为空。

Answer 1

AppService 的默认生命周期为 25 秒，除非前台体验请求它。当服务关闭连接时，您的客户端进程将收到 ServiceClosed 事件，因此您知道下次要发送请求时需要重新打开连接。