CODEWITHSUNDEEP
c#uwp
shawnseanshaun
shawnseanshaun

Reputation: 1107

UWP AppServiceConnection not getting value

I'm trying to communicate between my host app and service via AppServiceConnection. I'm using the following code in my host app:

using (var connection = new AppServiceConnection())
{
    connection.AppServiceName = extension.AppServiceName;
    connection.PackageFamilyName = extension.PackageFamilyName;

    var connectionStatus = await connection.OpenAsync();

    if (connectionStatus == AppServiceConnectionStatus.Success)
    {
        var response = await connection.SendMessageAsync(requestMessage);

        if (response.Status == AppServiceResponseStatus.Success)
            returnValue = response.Message as ValueSet;
    }
}

And my service code:

private async void OnRequestReceived(AppServiceConnection sender, AppServiceRequestReceivedEventArgs args)
{
    var messageDeferral = args.GetDeferral();
    var message = args.Request.Message;
    var returnData = new ValueSet();

    var command = message["Command"] as string;

    switch (command)
    {
        case "ACTION":
            var value = await AsyncAction();
            returnData = new ValueSet { { "Value", JsonConvert.SerializeObject(value) } };
            break;                
        default:
            break;
    }

    await args.Request.SendResponseAsync(returnData);
    messageDeferral.Complete();
}

This works some of the time, but other times the ValueSet (returnValue) is randomly empty when the host receives it. It has Value in it when returned in the service, but when I get the response in the host, nothing.

I've verified that the service is indeed setting the value, adding it to the ValueSet and returning it correctly.

Note that my service is receiving the request, the host is receiving the response and the response status is Success; a failed connection isn't the issue.

Sometimes this happens only once before requests start working again, other times it will happen ten times in a row.

The first working response after a failure always takes significantly longer than normal.

Also, I have no issues in the request from host to service. It's always service to host where the problem shows up.

Has anyone else run into this issue and figured it out?

Upvotes: 2

Views: 1098

Answers (1)

shawnseanshaun
shawnseanshaun

Reputation: 1107

In the process of creating a sample app I realized what the problem was. I was performing an asynchronous action (albeit a very short one) before my line var messageDeferral = args.GetDeferral();. It appears that this was allowing the background task to be closed before it had responded to the host. Simply moving that line to the beginning of the OnRequestReceived function fixed the problem for me.

So for anyone who runs into a similar issue, get your deferral before you do anything else! Spare yourself the pain I went through.

Upvotes: 6

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