Question

I have been looking for a reason, but about every single topic on stackoverflow I could find suggested a busy UI as the reason.
I have very basic code, just for testings and it simply won’t update the UI, even though I am sure it cannot be busy doing something else:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    static double t = 0;
    static double dt = 0.1;

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        Timer timer = new Timer(5000);
        timer.Enabled = true;
        timer.Elapsed += new ElapsedEventHandler(Update);
        timer.Start();
    }

    void Update(object sender, ElapsedEventArgs e)
    {
        t = t + dt;
        testBlock1.Text = (t).ToString();
    }
}

I debugged it and set a breakpoint to the textBlock1.Text update and it did break every 5 seconds, but the UI is never updated. As can be seen in the code, when I move my mouse over the Button I use to start the timer, the button shows its typical “mouse-over-button” animation. Why does that happen, but not the text update?

If anyone can lead me to a good topic on stackoverflow, please do so and I will delete my question here, but I couldn’t find any topic explaining why this approach doesn’t update the UI even though the UI is not busy doing anyting else.

Answer 1

For WPF, you should use DispatcherTimer –
Also with the above code you posted, i am getting a cross thread error since elapsed event is raised on other thread and not on UI thread.

private void button1_Click(object sender, RoutedEventArgs e)
{
   DispatcherTimer timer = new DispatcherTimer();
   timer.Interval = new TimeSpan(0, 0, 5);
   timer.Tick += new EventHandler(timer_Tick);
   timer.Start();
}

void timer_Tick(object sender, EventArgs e)
{
   t = t + dt;
   txt.Text = (t + dt).ToString();
}

EDIT

Also, you can marshal it on UI Dispatcher with your existing code like this –

void Update(object sender, ElapsedEventArgs e)
{
    App.Current.Dispatcher.Invoke((Action)delegate()
    {
        t = t + dt;
        txt.Text = (t + dt).ToString();
    });
}