private void FlexChart1_PointerPressed(object sender, PointerRoutedEventArgs e)
 {
     if (e.Pointer.PointerDeviceType == Windows.Devices.Input.PointerDeviceType.Mouse)
     {
         flexChart1.Focus(FocusState.Pointer);
         _flexChartContextMenu.Hide();
         var p = e.GetCurrentPoint((UIElement)sender);
         if (p.Properties.IsRightButtonPressed)
         {
             if (al.HitTest(e.GetCurrentPoint(flexChart1).Position) != null)
             {
                 al.SelectedAnnotation = al.HitTest(e.GetCurrentPoint(flexChart1).Position);
                 _flexChartContextMenu.Show(flexChart1, p.Position);
             }
         }
     }
 }