Thread Error while updating UI by calling method from IOT Hub

I am very new to C# and Azure IoT. Perhaps the problem I have is very simple to solve. I would like to update the an UI Element by invoking a method from the cloud. But I am getting the following Error:

The application called an interface that was marshalled for a different thread. (Exception from HRESULT: 0x8001010E (RPC_E_WRONG_THREAD))

I know t has something to do with the fact that the UI is running in another thread. but I didn´t find any solution.

Here the code

public sealed partial class MainPage : Page
{

    DeviceClient deviceClient;

    public MainPage()
    {
        this.InitializeComponent();
        deviceClient = DeviceClient.CreateFromConnectionString(GlobalConstant.DEVICE_CONNECTION_STRING, TransportType.Mqtt);
        deviceClient.SetMethodHandlerAsync("UpdateTextfield", UpdateTextfield, null);
    }

    private void updateTextField ()
    {
        IncomingMessage.Text = "Update";
    }

    private Task<MethodResponse> UpdateTextfield(MethodRequest methodRequest, object userContext)
    {
        updateTextField();
        string result = "{\"result\":\"Executed direct method: " + methodRequest.Name + "\"}";
        return Task.FromResult(new MethodResponse(Encoding.UTF8.GetBytes(result), 200));
    }
}

The process that you are calling the: IncomingMessage.Text = "Update"; is happening on a thread that is non-UI threads. You need to marshal the thread from the current executing thread to the UI thread.

Windows.UI.Core.CoreDispatcher can be used to this. Here is an example:

    using Windows.ApplicationModel.Core;

    private async void updateTextField ()
    {
        await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, ()=>{
            IncomingMessage.Text = "Update";
        });    
    }

Cross reference: "Run code on UI thread in WinRT"