Can't change background color out of TimedEvent();

Question

in my C# WPF project I have a timed Event. Inside the timedEvent I have multiple try catch function. For example this:

try
            {
                StreamWriter sw = new StreamWriter("Dateien/DB/Box" + boxnumber + "_Abwesenheit.txt", true, Encoding.ASCII);
                sw.Write("\n" + WNR_KNR[1] + datetime);
                sw.Close();
                Rec_Background.Fill = new SolidColorBrush(Color.FromRgb(255, 255, 0));
            }
            catch (Exception y)
            {
                Console.WriteLine("Exception; " + y.Message);
            }
            finally
            {
                Console.WriteLine("Abwesenheit automatisch Pause(1059)");
                absence = true;
            }

at Rec_background.Fill = new SolidColorBrush(Color.FromRgb(255, 255, 0));

I got a Exception thrown:

Exception thrown: 'System.InvalidOperationException' in WindowsBase.dll The thread 0xf4c has exited with code 0 (0x0). Exception; Der aufrufende Thread kann nicht auf dieses Objekt zugreifen, da sich das Objekt im Besitz eines anderen Threads befindet. The thread 0x4848 has exited with code 0 (0x0).

This exception is thrown multiple times in the timed Event. For example also when I try to write to text-file. But this is only happening in the TimedEvent no where else.

Answer 1

To put this Application.Current.Dispatcher.Invoke(() => before the Rec_background.... solved it.