Trying to understand what drives a refresh; timer versus Application.AddTimeout approach.

[dandole]

Hi, I'm trying to understand why these two variations on the same "concept" are not working identical.

This first one is a timer which runs UpdateLabel and SetNeedsDraw() on that label. Instead of updating every 100 milliseconds it only updates if the mouse is over the window or moving or lost/got focus; and not at a rate of every 100ms. It's like its ignoring the SetNeedsDraw() request and only refreshing because of some other events firing.

internal class Program
{
    private static readonly System.Timers.Timer _timer = new(100) { Enabled = false };
    private static readonly Window _window = new() { Title = "Test", Y = 1, Height = Dim.Fill(1) };
    private static readonly Label _labelView = new() { X = 0, Y = 0, Width = Dim.Fill(), Height = Dim.Fill(1) };
    static void Main(string[] args)
    {
        Application.Init();
        _window.Add(_labelView);
        UpdateLabel();
        _timer.Elapsed += (s, e) => 
        { 
            UpdateLabel(); 
            _labelView.SetNeedsDraw(); 
        };
        _timer.Start();
        Application.Run(_window);
        _timer.Stop();
        Application.Shutdown();
    }
    private static void UpdateLabel()
    {
        _labelView.Text = DateTime.Now.ToString("s.fff") + "\n";
        for (int i = 0; i < 10; i++)
            _labelView.Text += new string(' ', i) + DateTime.Now.ToString("T") + "\n";
    }
}

Versus this second one; which instead of the timer, uses Application.AddTimeout and updates the window every 100 milliseconds as expected. So wondering why the timer based approach doesnt give the same result as the below.

internal class Program
{
    private static readonly Window _window = new() { Title = "Test", Y = 1, Height = Dim.Fill(1) };
    private static readonly Label _labelView = new() { X = 0, Y = 0, Width = Dim.Fill(), Height = Dim.Fill(1) };
    static void Main(string[] args)
    {
        Application.Init();
        _window.Add(_labelView);
        UpdateLabel();

        Application.AddTimeout(TimeSpan.FromMilliseconds(100),
            () =>
            {
                UpdateLabel();
                return true;
            });

        Application.Run(_window);
        Application.Shutdown();
    }

    private static void UpdateLabel()
    {
        _labelView.Text = DateTime.Now.ToString("s.fff") + "\n";
        for (int i = 0; i < 10; i++)
            _labelView.Text += new string(' ', i) + DateTime.Now.ToString("T") + "\n";
    }
}

Thanks!

[BDisp]

Because Application.AddTimeout force an iteration which will redraw again. For the timer work as well you have to call Application.Invoke inside the Elapsed event.

        _timer.Elapsed += (s, e) => 
        { 
            Application.Invoke(() => {
                UpdateLabel(); 
                _labelView.SetNeedsDraw(); 
            });
        };

[dandole]

Thanks!!! Got it. And it appears I don't have to call SetNeedsDraw() for it to work either. This worked:

        _timer.Elapsed += (s, e) =>
        {
            Application.Invoke(() =>
            {
                UpdateLabel();
            });
        };

[tznind]

Yup! This is exactly right. UI changes should only be made from the UI thread.

If you are on background thread e.g. in the timer, then you must 'queue' the work using the Invoke. That work will then be run on main UI thread during next 'iteration' of the main loop.