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

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        var yoba = new Yoba();
        yoba.YobaSpeaks += YobaOnYobaSpeaks;
    }

    private void YobaOnYobaSpeaks(object sender, YobaEventArgs yobaEventArgs)
    {
        Dispatcher.Invoke(() => tb.Text += yobaEventArgs.NewMessage + Environment.NewLine);
    }
}

#######################

public class YobaEventArgs : EventArgs
{
    public string NewMessage { get; set; }

    public YobaEventArgs(string message)
    {
        NewMessage = message;
    }
}

public class Yoba
{
    private Timer timer;

    public event EventHandler<YobaEventArgs> YobaSpeaks;

    protected virtual void OnYobaSpeaks(YobaEventArgs e)
    {
        var handler = YobaSpeaks;
        if (handler != null) handler(this, e);
    }

    public Yoba()
    {
        timer = new Timer(1000);
        timer.Elapsed += TimerOnElapsed;
        timer.Enabled = true;
    }

    private void TimerOnElapsed(object sender, ElapsedEventArgs elapsedEventArgs)
    {
        var message = "yoba, eto ti?";
        OnYobaSpeaks(new YobaEventArgs(message));
    }
}