How do I generate a call to the UI thread on an ETO application using C#?

Question

I want to build a cross platform GUI app for linux and windows. ETO was recommended https://github.com/picoe/Eto I'm pretty used to winforms, but I'm stuck trying to get ETO to respond to a repeated call from a timer. The examples I've found require using the winforms this.InvokeRequired, which doesn't exist under Linux.

I want a timer to start up and send a signal to update the GUI textbox every 100ms.

I have this:

// This timer needs to kick off every 100ms to update the GUI.
Timer myTimer = new Timer(TimerTick, // the callback function
new object(),
0,
100); // Every 100ms

private static void TimerTick(object state)
{
    if (ProcessTics == true)
    { Task.Factory.StartNew(CallTheBackgroundFunctions); }

}


private static void CallTheBackgroundFunctions()
{
    OtherClass.ProcessTic();
    mainTextDisplay.Text = OtherClass.GetText(); //This errors out
}

The problem is the timer is a static instance and I've written my OtherClass as a static instance. If I provide a reference to the main form, this.Invalidate(); doesn't update the gui.

I believe I need to use ETO's invoke, but I'm really struggling to make it work.

Any suggestions for a good way to have a background thread update the GUI on an ETO form? Or suggestions for another cross platform GUI framework that supports C#? This is all for a text processing project.

Thank you for your time.

Answer 1

The real trick was to properly call Application.Instance.Invoke delegate.
In case anyone else runs into a similar issue, here's how I arranged the classes to update a textbox from another thread.

public static class TextRender
{   
    public delegate void BroadCastText(object sender, EventArgs e, string message);
    public static BroadCastText Broadcasting;



    public static void ProcessTic()
    {       
        string outboundText = "";
        // do some behind the scenes work.

        if (Broadcasting != null) // Verify someone has subscribed to the event, otherwise null object error.
        {
            Broadcasting(null, EventArgs.Empty, outboundText);
        }
        else
        {
            Console.WriteLine("I'm talking but no one is listening!!");
        }
    }
}

public class MainForm : Form
{
    Timer myTimer; // High resolution timer.
    UITimer UITimerTick = new UITimer(); // Low resolution timer, but runs on the UI thread.
    TextArea mainTextDisplay = new TextArea(); // Textbox that needs to be updated in realtime.
    

    
   private static void TimerTick(object state)
   {
       TextRender.ProcessTic();
   }


   /// <summary>
   /// Takes the incoming string and uses the UI thread to update the display.
   /// </summary>
   /// <param name="sender"></param>
   /// <param name="e"></param>
   /// <param name="message"></param>
   private void WriteTextDelegate(Object sender, EventArgs e, string message)
   {
       Application.Instance.Invoke(delegate {
           mainTextDisplay.Text = message;
       });
   }

   /// <summary>
   /// Toggles a timer that performs a callback to update the UI.
   /// </summary>
   private void Timer1()
   {
       if (Timer1Active)
       {
           TextRender.Broadcasting -= WriteTextDelegate;
           myTimer.Dispose();
           Timer1Active = false;
       }
       else
       {
           myTimer = new Timer(TimerTick, // the callback function
           new object(), 
           0, // the time to wait before the timer starts it's first tick
           50); // the tick interval

           TextRender.Broadcasting += WriteTextDelegate;  //  Subscribe to the event
           Timer1Active = true;
           Console.WriteLine("Timer 1 start");
       }
   }

   /// <summary>
   /// Toggles using the UI timer solution.  This is not intended to update faster than 1 per second.  
   /// </summary>
   private void Timer2()
   {
       if (Timer2Active)
       {
           UITimerTick.Stop();
           UITimerTick.Dispose();
           Timer2Active = false;
       }
       else
       {
           UITimerTick.Interval = 0.5;  //half second refresh.  Can't go any faster without window freezing.
           UITimerTick.Elapsed += (sender, ev) =>
           {
               TextRender.ProcessTic();
               mainTextDisplay.Text = TextRender.CachedText;
           };
           
           UITimerTick.Start();
           Timer2Active = true;
           Console.WriteLine("Timer 2 start.");
       }
   }

}

Answer 2

To invoke a method on the UI thread, use Eto.Forms.Application.Instance.Invoke() or Eto.Forms.Application.Instance.AsyncInvoke(). The latter of which will schedule the call and return immediately.

Alternatively, for this type of scenario you can also use Eto.Forms.UITimer instead, which schedules its event on the main loop.