Retrieving a dp value from another task

I'm using a dp, and I created 2 tasks.

In task1, I new a TestClass. In task2, I want to get Num value, but got error:

Exception thrown: 'System.InvalidOperationException' in WindowsBase.dll
An exception of type 'System.InvalidOperationException' occurred in WindowsBase.dll but was not handled in user code
The calling thread cannot access this object because a different thread owns it.

Note, they must be in different thread for some reason. Actually there are 3 threads, I just made a sample to reproduce it.

namespace WpfApp1 { /// /// Interaction logic for MainWindow.xaml /// public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            var task1 = new Task(Test1);
            task1.Start();

            var task2 = new Task(Test2);
            task2.Start();

            task1.Wait();
            task2.Wait();
        }

        private TestClass another = null;
        private AutoResetEvent autoResetEvent = new AutoResetEvent(false);

        private void Test1()
        {
            another = new TestClass();
            autoResetEvent.Set();
        }

        private void Test2()
        {
            //Task.Delay(1000);
            autoResetEvent.WaitOne();

            int k = 0;
            k = another.Num;
        }

    }

    public class TestClass : DependencyObject
    {
        public int Num
        {
            get
            {
                return (int)GetValue(NumProperty);
            }
            set { SetValue(NumProperty, value); }
        }

        public static readonly DependencyProperty NumProperty =
            DependencyProperty.Register("Num", typeof(int), typeof(TestClass), new PropertyMetadata(10));
    }
}

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