Hit testing on child of InkCanvas

Question

I have added a button to an InkCanvas by way of code-behind. For reasons I can not understand,

    HitTestResult result = VisualTreeHelper.HitTest(pe.InkCanvas.Children[2], point_MouseDown);

where the button has index of 2, always results in result being null when I click over the button.

Anybody know how to determine if a child element has been clicked on?

Any help will be appreciated. (Yes, I have searched the internet without success. I apologize if this seems a dumb question).

System: Windows 7, .net4.0 WPF C#

Edit: If I do the same thing where Children[0] is a RichTextBox, then the above HitTest resturns non-null. Anybody with any idea why?

Edit: Both the RichTextBox and the Button are added in code-behind, the XAML is:

 <Grid Height="{x:Static local:pe.heightCanvas}" >

            <!--NotepadCanvas. Canvas used to place user writing lines and borders.-->
            <Canvas Name="NotePadCanvas" Panel.ZIndex="0"
                     Width="{x:Static local:pe.widthCanvas}" 
                     Height="{x:Static local:pe.heightCanvas}" 
                     Background="{Binding documenttype, Converter={StaticResource inkCanvasBackgroundConverter}}" />

            <!--BackgroundCanvas. Canvas used for special highlighting of seleted items-->
            <Canvas Name="BackgroundCanvas" Panel.ZIndex="1"
                     Width="{x:Static local:pe.widthCanvas}" 
                     Height="{x:Static local:pe.heightCanvas}" 
                     Background="Transparent" />

            <!--FormsCanvas. Canvas used to place formatted text from lists, etc.-->
            <Canvas Name="FormsCanvas" Panel.ZIndex="2"
                     Width="{x:Static local:pe.widthCanvas}" 
                     Height="{x:Static local:pe.heightCanvas}" 
                     Background="Transparent" />

            <!--TranscriptionCanvas. Canvas used to place recognized ink from the InkAnalyzer-->
            <Canvas Name="TranscriptionCanvas" Panel.ZIndex="3"
                     Width="{x:Static local:pe.widthCanvas}" 
                     Height="{x:Static local:pe.heightCanvas}" 
                     Background="Transparent" />

            <!--InkCanv. Top most canvas used to gather handwritten ink strokes from the user. EditingMode="Ink"   Gesture="OnGesture" -->
            <local:CustomInkCanvas x:Name="InkCanvas" Panel.ZIndex="4" 
                       Width="{x:Static local:pe.widthCanvas}"
                       Height ="{x:Static local:pe.heightCanvas}" 
                       Background="Transparent" 
                       AllowDrop="True"  Drop="InkCanvas_Drop"/>

        </Grid>

could you share your xaml tree? so we may have a look and try to simulate. — pushpraj, Jun 11 '14 at 04:15

score 0 · Answer 1 · answered Jun 11 '14 at 04:26

This works but it seems convoluted and I don't know why a button shows up as a TextBlock:

...........

  Button btn = new Button();
        btn.Name = "Cancel";
        btn.Content = "Cancel";
        btn.Background = Brushes.Red;
        btn.Width = 50;
        btn.Height = 25;
        btn.RenderTransform = new System.Windows.Media.TranslateTransform(pe.InkCanvas.ActualWidth-btn.Width,topmargin);

        btnCancel = btn;
        pe.InkCanvas.Children.Add(btnCancel);

Then, in the PreviewMouseLeftButtonDown() (code modified slightly from Microsoft's site) ...............

// Clear the contents of the list used for hit test results.
                hitResultsList.Clear();


                // Set up a callback to receive the hit test result enumeration.
                VisualTreeHelper.HitTest(pe.InkCanvas, null,
                    new HitTestResultCallback(MyHitTestResult),                        new PointHitTestParameters(point_MouseDown));

                for (int i = 0; i < hitResultsList.Count; i++)
                {
                    TextBlock tb = hitResultsList[i] as TextBlock;
                    if (tb == null) continue;
                    if (tb.Text == "Cancel")
                    {
                        Cancel_Click(); 
                    }
                }

..................................................

List<DependencyObject> hitResultsList = new List<DependencyObject>();

    // Return the result of the hit test to the callback. 
    public HitTestResultBehavior MyHitTestResult(HitTestResult result)
    {
        // Add the hit test result to the list that will be processed after the enumeration.
        hitResultsList.Add(result.VisualHit);

        // Set the behavior to return visuals at all z-order levels. 
        return HitTestResultBehavior.Continue;
    }

Is there a better way? And why does the button show up as a TextBlock?

Hit testing on child of InkCanvas

1 Answers1