我如何针对TabControl选项卡进行测试？

Question

给定一个相对于Page的点，我如何针对TabControl的选项卡进行测试？ VisualTreeHelper.HitTest给了我内容，但是当我走上视觉树时，我看不到任何可以告诉我实际上已经碰到标签的东西。我甚至看不到标签控件本身。

public class ViewManipulationAgent : IDisposable
{
    private const int _limit = 125;

    private INavigationService _navigationService;

    private FrameworkElement _container;
    private FrameworkElement _element;

    private TranslateTransform _translate;

    private IInputElement _touchTarget;


    // When I use this object, 
    // a_container is the main Frame control in my application. 
    // a_element is a page within that frame.
    public ViewManipulationAgent(FrameworkElement a_container, FrameworkElement a_element)
    {
        _navigationService = a_navigationService;
        _container = a_container;
        _element = a_element;

        // Since I set IsManipulationEnabled to true all touch commands are suspended
        // for all commands on the page (a_element) unless I specifically cancel (see below)
        _element.IsManipulationEnabled = true;
        _element.PreviewTouchDown += OnElementPreviewTouchDown;
        _element.ManipulationStarting += OnElementManipulationStarting;
        _element.ManipulationDelta += OnElementManipulationDelta;
        _element.ManipulationCompleted += OnElementManipulationCompleted;

        _translate = new TranslateTransform(0.0, 0.0);
        _element.RenderTransform = _translate;
    }


    // Since the ManipulationStarting doesn't provide position I capture the position
    // here and then hit test elements to find any controls for which I want to bypass
    // manipulation.
    private void OnElementPreviewTouchDown(object sender, TouchEventArgs e)
    {
        var position = e.GetTouchPoint(_element).Position;

        _touchTarget = null;
        HitTestResult result = VisualTreeHelper.HitTest(_element, position);

        if (result.VisualHit == null)
            return;

        var button = VisualTreeHelperEx.FindAncestorByType<ButtonBase>(result.VisualHit) as ButtonBase;
        if (button != null)
        {
            _touchTarget = button;
            return;
        }

        var slider = VisualTreeHelperEx.FindAncestorByType<Slider>(result.VisualHit) as Slider;
        if (slider != null)
        {
            _touchTarget = slider;
            return;
        }
    }

    // Here is where I cancel manipulation if a specific touch target was found in the 
    // above event.
    private void OnElementManipulationStarting(object sender, ManipulationStartingEventArgs e)
    {
        if (_touchTarget != null)
        {
            e.Cancel(); // <- I have to cancel manipulation or the buttons and other 
                        //    controls cannot be manipulated by the touch interface.
            return;
        }

        e.ManipulationContainer = _container;
    }

    private void OnElementManipulationDelta(object sender, ManipulationDeltaEventArgs e)
    {
        var element = e.Source as FrameworkElement;

        if (element == null)
            return;

        var translate = _translate.X + e.DeltaManipulation.Translation.X;


        if (translate > _limit)
        {
            GoBack();

            translate = _limit;
        }

        if (translate < -_limit)
        {
            GoForward();

            translate = -_limit;
        }

        _translate.X = translate;

    }

    private void GoForward()
    {
        var navigationService = ServiceLocator.Current.GetInstance<INavigationService>();

        navigationService.GoForward();
    }

    private void GoBack()
    {
        var navigationService = ServiceLocator.Current.GetInstance<INavigationService>();

        navigationService.GoBack();
    }

    private void OnElementManipulationCompleted(object sender, ManipulationCompletedEventArgs e)
    {
        _touchTarget = null;

        _translate.X = 0;
    }

    public void Dispose()
    {
        _element.PreviewTouchDown -= OnElementPreviewTouchDown;
        _element.ManipulationStarting -= OnElementManipulationStarting;
        _element.ManipulationDelta -= OnElementManipulationDelta;
        _element.ManipulationCompleted -= OnElementManipulationCompleted;
    }

}