无法将类型“System.Threading.Tasks.Task”隐式转换为“Windows.Foundation.IAsyncAction”。 存在显式转换

Question

So I'm coding this software in C# and I get hit with this error message. For the life of me, I cannot figure it out and searching is not bringing up anything useful, no matter what I do.

The code itself:

private async Task LoginIoTHub()
{
    TypeJson command_json = new TypeJson();

    if (NowNetSta == false) return;
    if (IoTHubConnectFlag == false) return;

    if (TeamName == null)
    {
        Debug.WriteLine("Please don't let your team name be void when you call methods 'new IoTHubLocalService(xx,xx,xx)'");
        await Task.Delay(TimeSpan.FromSeconds(4));
    }
    else
    {
        if (LoginF == false)
        {
            try
            {
                Debug.WriteLine("Start to login\r\n");

                LoginJson login_msg = new LoginJson();
                login_msg.DeviceID = BoardID;
                login_msg.name = TeamName;

                var messageString = JsonConvert.SerializeObject(login_msg);

                command_json.Type = 1;
                command_json.Command = messageString;
                messageString = JsonConvert.SerializeObject(command_json);

                var message = new Message(Encoding.ASCII.GetBytes(messageString));
                IAsyncAction Action = deviceClient.SendEventAsync(message);

                await Action;

                if (Action.Status == AsyncStatus.Completed)
                {
                    Debug.WriteLine("Login success");
                    LoginF = true;
                }
                else
                {
                    Debug.WriteLine("Login failed");
                    await Task.Delay(TimeSpan.FromSeconds(10));
                }
            }

            catch (Exception ex)
            {
                Debug.WriteLine("Login to IoT Hub failed, please check your team name and internet connection: " + ex.Message);
                await Task.Delay(TimeSpan.FromSeconds(10));
            }
        }
    }
}

Answer 1

DeviceClient.SendEventAsync(Message) returns a Task

Sends an event to device hub

public Task SendEventAsync(Message message)

change code to

var Action = deviceClient.SendEventAsync(message);
await Action;

Also note that Task inherits from IAsyncResult and not IAsyncAction like in your example.

You can also check completion using Task.IsCompleted Property

if (Action.IsCompleted) { ...

Answer 2

Your problem is here:

IAsyncAction Action = deviceClient.SendEventAsync(message);

Async method calls return Tasks. Not IAsyncActions.

Assuming the return value of your function call deviceClient.SendEventAsync(message) is a Task<IAsyncAction> you should updated your code to this:

IAsyncAction Action = await deviceClient.SendEventAsync(message);

Reference: https://msdn.microsoft.com/en-us/library/mt674882.aspx

Answer 3

Your problem is this line:

IAsyncAction Action = deviceClient.SendEventAsync(message);

SendEventAsync return a Task wether you expect a IAsyncAction. If an explicit conversion exists you can do the following:

IAsyncAction Action = deviceClient.SendEventAsync(message) as IAsyncResult;

But I think SendEventAsync returns Task<IAsyncAction> inside which means you have to await it:

IAsyncAction Action = await deviceClient.SendEventAsync(message);

Based on your comment:

I tried this, believe it or not. It throws another error though: "Cannot implicitly convert type 'void' to 'Windows.Foundation.IASyncAction'.

I would guess that you just don't get a IAsyncAction. So you have to do it this way:

await deviceClient.SendEventAsync(message);