How to: Determine the Document Element under the Mouse Pointer

• Nov 26, 2024
• 3 minutes to read

This code example uses the HitTestManager.HitTest method to find information about an element under the mouse pointer. The method returns a RichEditHitTestResult instance. This instance contains details about a specific document element (the RichEditHitTestResult.LayoutElement object) located under the test point. It lets you identify the element’s type and the area it occupies in the document.

In this example, the ToolTipController displays the element information. Handle the ToolTipController.GetActiveObjectInfo event. This makes the ToolTip show details about the hovered element. Here is an example:

View Example: How to Show a ToolTip With Information About the Document Element Located Under the Cursor Position

Form1.cs

void ToolTipController_GetActiveObjectInfo(object sender, ToolTipControllerGetActiveObjectInfoEventArgs e)
{
    if (!e.SelectedControl.Equals(richEditControl1))
        return;

    // Obtain the mouse cursor's layout position on the page and the current page index:
    PageLayoutPosition pageLayoutPosition =
        richEditControl1.ActiveView.GetDocumentLayoutPosition(e.ControlMousePosition);
    if (pageLayoutPosition == null)
        return;            

    Point point = pageLayoutPosition.Position;  
    int pageIndex = pageLayoutPosition.PageIndex;
    LayoutPage layoutPage = richEditControl1.DocumentLayout.GetPage(pageIndex);

    // Create a HitTestManager instance: 
    HitTestManager hitTest = new HitTestManager(richEditControl1.DocumentLayout);

    // Perform the hit test and pass the result to the RichEditHitTestResult object:
    RichEditHitTestResult result = hitTest.HitTest(layoutPage, point);
    if (result != null)
    {
        // Retrieve the current layout element type:
        LayoutElement element = result.LayoutElement;
        string text = element.Type.ToString();

        // Obtain the the text character and its bounds under the mouse position              
        if (element.Type == LayoutType.CharacterBox)
        {
            text += String.Format(" : \"{0}\"", (element as CharacterBox).Text);
            text += GetBounds(element);
            if (element.Parent.Type == LayoutType.PlainTextBox)
            {
                text += String.Format("\r\nPlainTextBox : \"{0}\"", (element.Parent as PlainTextBox).Text);
                text += GetBounds(element.Parent);
            }
        }
        else
        {
            // Get the hovered element's bounds:
            text += GetBounds(element);
        }

        // Get the element's location:
        string title = GetLocation(element);

        // Display all retrieved information in the tooltip:
        e.Info = new ToolTipControlInfo(element.Bounds, text, title, ToolTipIconType.Information);        
    }
}

string GetBounds(LayoutElement element)
{
    return String.Format("\r\nBounds : {0}", element.Bounds);
}
string GetLocation(LayoutElement element)
{
    while (element != null)
    {
        switch (element.Type)
        {
            case LayoutType.CommentsArea:
                return "Comments Area Location";
            case LayoutType.Header:
                return "Header Location";
            case LayoutType.Footer:
                return "Footer Location";
        }
        element = element.Parent;
    }
    return "Page Location";
}        

Form1.vb

 Private Sub ToolTipController_GetActiveObjectInfo(ByVal sender As Object, ByVal e As ToolTipControllerGetActiveObjectInfoEventArgs)
    If Not e.SelectedControl.Equals(richEditControl1) Then
        Return
    End If

    ' Obtain the mouse cursor's layout position on the page and the current page index:
    Dim pageLayoutPosition As PageLayoutPosition =
         richEditControl1.ActiveView.GetDocumentLayoutPosition(e.ControlMousePosition)
    If pageLayoutPosition Is Nothing Then
        Return
    End If

    Dim point As Point = pageLayoutPosition.Position
    Dim pageIndex As Integer = pageLayoutPosition.PageIndex
    Dim layoutPage As LayoutPage = richEditControl1.DocumentLayout.GetPage(pageIndex)

    ' Create a HitTestManager instance: 
    Dim hitTest As New HitTestManager(richEditControl1.DocumentLayout)

    ' Perform the hit test and pass the result to the RichEditHitTestResult object:
    Dim result As RichEditHitTestResult = hitTest.HitTest(layoutPage, point)
    If result IsNot Nothing Then
        ' Retrieve the current layout element type:
        Dim element As LayoutElement = result.LayoutElement
        Dim text As String = element.Type.ToString()

        ' Obtain the the text character and its bounds under the mouse position              
        If element.Type = LayoutType.CharacterBox Then
            text &= String.Format(" : ""{0}""", (TryCast(element, CharacterBox)).Text)
            text &= GetBounds(element)
            If element.Parent.Type = LayoutType.PlainTextBox Then
                text &= String.Format(ControlChars.CrLf & "PlainTextBox : ""{0}""", (TryCast(element.Parent, PlainTextBox)).Text)
                text &= GetBounds(element.Parent)
            End If
        Else
            ' Get the hovered element's bounds:
            text &= GetBounds(element)
        End If

        ' Get the element's location:
        Dim title As String = GetLocation(element)

        ' Display all retrieved information in the tooltip:
        e.Info = New ToolTipControlInfo(element.Bounds, text, title, ToolTipIconType.Information)
    End If
End Sub

Private Function GetBounds(ByVal element As LayoutElement) As String
    Return String.Format(ControlChars.CrLf & "Bounds : {0}", element.Bounds)
End Function
Private Function GetLocation(ByVal element As LayoutElement) As String
    Do While element IsNot Nothing
        Select Case element.Type
            Case LayoutType.CommentsArea
                Return "Comments Area Location"
            Case LayoutType.Header
                Return "Header Location"
            Case LayoutType.Footer
                Return "Footer Location"
        End Select
        element = element.Parent
    Loop
    Return "Page Location"
End Function