Simpliest code: Can't change label "Content" programmatically

Pew_new

Hello everyone. Currently I am trying to work with timers in WPF.

private void Window_Loaded(object sender, RoutedEventArgs e)
{
_timer = new System.Timers.Timer();
_timer.Interval = 1000;
_timer.Elapsed += OnTimerElapsed;
_timer.Start();

    }

    int i=0;
    private void OnTimerElapsed(object sender, ElapsedEventArgs e)
    {
        i++;

        label1.Content = i.ToString();

    }

I've got an exception at this string

label1.Content = i.ToString();

What I'm doing wrong with a label? Thanks in advance! XAML:

Bernhard Hiller

Pew_new wrote:

What I'm doing wrong with a label?

You access it from a different thread - you must not do that, and that holds true also for other UI technologies like WinForms. With WPF also comes MVVM. Instead of setting the Content property directly, you bind it to some property of your view model. When that property changes, you raise an PropertyChanged event, and that will do the magic of "transporting" the change in the correct thread.

Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!

Pew_new

Please explain where have you seen " different thread"? "different thread", you mean that with a System.Timer it's not possible? P.S. Here https://www.youtube.com/watch?v=QkT8fgoFz3g, a guy is doing that easily. True he's using a Dispatcher Timer. So what's difference?

Richard Deeming

The DispatcherTimer documentation makes things slightly clearer than the System.Timers.Timer documentation:

DispatcherTimer Class (System.Windows.Threading) | Microsoft Docs[^]:

If a System.Timers.Timer is used in a WPF application, it is worth noting that the System.Timers.Timer runs on a different thread than the user interface (UI) thread. In order to access objects on the user interface (UI) thread, it is necessary to post the operation onto the Dispatcher of the user interface (UI) thread using Invoke or BeginInvoke. Reasons for using a DispatcherTimer as opposed to a System.Timers.Timer are that the DispatcherTimer runs on the same thread as the Dispatcher and a DispatcherPriority can be set on the DispatcherTimer.

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