Calling server-side device methods from the client-hosted device UI

VS Project: ProxySample1.zip

Connexion 14.5+ includes a framework to communicate directly with your server-side device from the associated device user-interface. This is often useful if you need to query for server-side state, perform a database lookup or connection availability, or run a specific method on the server.

In order to utilize these service calls, the following steps are required:

Create an interface which defines all the methods implemented by the server-side device which the client UI will call
Implement this interface in your server-side device
Create a proxy variable in your device viewmodal class and use this to invoke the remote calls

In this example, we're going to add a diagnostics button to a device UI which will call our server-side device and display the resulting text.

First, create the interface:

  public interface IDiagnostics
  {
    Task<string> GetDiagnosticsAsync();
  }

Next, implement the interface in your device:

using System;
using System.Threading;
using Connexion.Core;
using System.Threading.Tasks;
namespace ProxySample1
{
  [DevicePlugin("ProxySample1", "Example of device proxying", DeviceDefinitionFlags.None, typeof(object), typeof(object), typeof(ProxySample1Factory))]
  public class ProxySample1 : BaseDevice<ProxySample1Configuration>, IDiagnostics
  {
    public override void Start()
    {
    }
    public override void Stop()
    {
    }
    public override async Task ProcessMessageAsync(IMessageContext context, CancellationToken token)
    {
    }
   
    public async Task<string> GetDiagnosticsAsync()
    {
      return Task.FromResult(Environment.MachineName);
    }
  }
}

Now, create a proxy variable in your viewmodel. Note that we recommend you perform proxy calls on a different thread so that you do not block the UI thread.

using Connexion.Core;
using System.Threading.Tasks;
using System.Windows.Input;
namespace ProxySample1
{
  public class ProxySample1UIViewModel : ViewModelBase
  {
    private ProxySample1Configuration m_Config;
    private IDeviceUIParams m_DeviceUIParams;
    private IDiagnostics m_Proxy;
    public ProxySample1UIViewModel(ProxySample1Configuration config, IDeviceUIParams deviceUIParams)
    {
      m_Config = config;
      m_DeviceUIParams = deviceUIParams;
      m_Proxy = deviceUIParams.GetServerDeviceProxy<IDiagnostics>(); // <-- creation of the proxy
    }
    public ProxySample1Configuration Configuration
    {
      get { return m_Config; }
    }
    private RelayCommand m_GetDiagnosticsCommand;
    public ICommand GetDiagnosticsCommand
    {
      get { return m_GetDiagnosticsCommand ?? (m_GetDiagnosticsCommand = new RelayCommand(async p => await GetDiagnostics())); }
    }
    private async Task GetDiagnostics()
    {
		try
		{
			DiagnosticResult = await m_Proxy.GetDiagnosticsAsync();	// <-- Calling the server
		}
		catch(exception ex)
		{
			DiagnosticResult = ex.Message;
		}
    }    
    private string m_DiagnosticResult = "Click to run the diagnostics";
    public string DiagnosticResult
    {
      get { return m_DiagnosticResult; }
      set
      {
        if(m_DiagnosticResult != value)
        {
          m_DiagnosticResult = value;
          RaisePropertyChanged();
        }
      }
    }
  }
}

Now we'll create the button and text box on the UI:

<UserControl x:Class="ProxySample1.ProxySample1UI"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300"
             Padding="6">
    <Border Margin="10">
        <StackPanel>
            <Button Command="{Binding GetDiagnosticsCommand}"
                    Content="Get Diagnostics" />

            <TextBox Text="{Binding DiagnosticResult, Mode=OneWay}"
                     IsReadOnly="True"
                     Margin="0,10,0,0"
                     MinHeight="200"
                     VerticalContentAlignment="Top"/>
        </StackPanel>
    </Border>
</UserControl>

When clicking the button, we now get the following result:

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Calling server-side device methods from the client-hosted device UI

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