ComponentOne WPF Edition
Working with WPF RichTextBox / Hit-Testing
Hit-Testing

The C1RichTextBox supports hyperlinks, which provide a standard mechanism for implementing user interactivity. In some cases, you may want to go beyond that and provide additional, custom mouse interactions. For example, you may want to apply some custom formatting or show a context menu when the user clicks an element.

To enable these scenarios, the C1RichTextBox exposes ElementMouse* events and a C1RichTextBox.GetPositionFromPoint method.

If all you need to know is the element that triggered the mouse event, you can get it from the source parameter in the event handler. If you need more detailed information (the specific word that was clicked within the element for example), then you need the C1RichTextBox.GetPositionFromPoint method. C1RichTextBox.GetPositionFromPoint takes a point in client coordinates and returns a C1TextPosition object that expresses the position in document coordinates.

The C1TextPosition object has two main properties: Element and Offset. The Element property represents an element within the document; Offset is a character index (if the element is a C1Run) or the index of the child element at the given point.

In the following section learn how to implement Hit Testing in RichTextBox .NET and .NET Framework versions.

 For example, the code below creates a C1RichTextBox and attaches a handler to the C1RichTextBox.ElementMouseLeftButtonDown event:
Visual Basic
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Public Sub New()
    ' Default initialization
    InitializeComponent()

    ' Create a C1RichTextBox and add it to the page
    _rtb = New C1RichTextBox()
    LayoutRoot.Children.Add(_rtb)

    ' Attach event handler
    Add Handler _rtb.ElementMouseLeftButtonDown AddressOf rtb_ElementMouseLeftButtonDown
End Sub
C#
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public MainPage()
{
  // Default initialization
  InitializeComponent();

  // Create a C1RichTextBox and add it to the page
  _rtb = new C1RichTextBox();
  LayoutRoot.Children.Add(_rtb);

  // Attach event handler
  _rtb.ElementMouseLeftButtonDown += rtb_ElementMouseLeftButtonDown;
}

The event handler below toggles the C1TextElement.FontWeight property for the entire element that was clicked. This could be a word, a sentence, or a whole paragraph:

Visual Basic
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Private Sub _rtb_ElementMouseLeftButtonDown(sender As Object, e As MouseButtonEventArgs)
    If Keyboard.Modifiers <> 0 Then
        Dim run = TryCast(sender, C1Run)
        If run IsNot Nothing Then
            run.FontWeight = If(run.FontWeight = FontWeights.Bold, FontWeights.Normal, FontWeights.Bold)
        End If
    End If
End Sub
C#
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void _rtb_ElementMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
  if (Keyboard.Modifiers != 0)
  {
    var run = sender as C1Run;
    if (run != null)
    {
      run.FontWeight = run.FontWeight == FontWeights.Bold
        ? FontWeights.Normal
        : FontWeights.Bold;
    }
  }
}

The code gets the element that was clicked by casting the sender parameter to a C1Run object.

If you wanted to toggle the C1TextElement.FontWeight value of a single word instead, then you would need to determine which character was clicked and expand the selection to the whole word. This is where the C1RichTextBox.GetPositionFromPoint method becomes necessary. Here is a revised version of the event handler that accomplishes that:

Visual Basic
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Private Sub _rtb_ElementMouseLeftButtonDown(sender As Object, e As MouseButtonEventArgs)
    If Keyboard.Modifiers <> 0 Then
        ' Get position in control coordinates
        Dim pt = e.GetPosition(_rtb)

        ' Get text pointer at position
        Dim pointer = _rtb.GetPositionFromPoint(pt)

        ' Check that the pointer is pointing to a C1Run
        Dim run = TryCast(pointer.Element, C1Run)
        If run IsNot Nothing Then
            ' Get the word within the C1Run
            Dim text = run.Text
            Dim start = pointer.Offset
            Dim [end] = pointer.Offset
            While start > 0 AndAlso Char.IsLetterOrDigit(text, start - 1)
                start -= 1
            End While
            While [end] < text.Length - 1 AndAlso Char.IsLetterOrDigit(text, [end] + 1)
                [end] += 1
            End While

            ' Toggle the bold property for the run that was clicked
            Dim word = New C1TextRange(pointer.Element, start, [end] - start + 1)
            word.FontWeight = If(word.FontWeight.HasValue AndAlso word.FontWeight.Value = FontWeights.Bold, FontWeights.Normal, FontWeights.Bold)
        End If
    End If
End Sub
C#
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void _rtb_ElementMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
  if (Keyboard.Modifiers != 0)
  {
    // Get position in control coordinates
    var pt = e.GetPosition(_rtb);

    // Get text pointer at position
    var pointer = _rtb.GetPositionFromPoint(pt);

    // Check that the pointer is pointing to a C1Run
    var run = pointer.Element as C1Run;
    if (run != null)
    {
      // Get the word within the C1Run
      var text = run.Text;
      var start = pointer.Offset;
      var end = pointer.Offset;
      while (start > 0 && char.IsLetterOrDigit(text, start - 1))
        start--;
      while (end < text.Length - 1 && char.IsLetterOrDigit(text, end + 1))
        end++;

      // Toggle the bold property for the run that was clicked
      var word = new C1TextRange(pointer.Element, start, end - start + 1);
      word.FontWeight =
        word.FontWeight.HasValue && word.FontWeight.Value == FontWeights.Bold
          ? FontWeights.Normal
          : FontWeights.Bold;
    }
  }
}

Notice that the C1TextElement.FontWeight property returns a nullable value. If the range contains a mix of values for this attribute, the property returns null. The code used to toggle the FontWeight property is the same we used earlier when implementing the formatting toolbar.

The GetPositionFromPoint allows you to get a C1TextPosition object from a point on the screen. The GetRectFromPosition method performs the reverse operation, returning a Rect that represents the screen position of a C1TextPosition object. This is useful in situations where you want to present a UI element near a specific portion of a document.