Intercepting HTML Link Click in RadChat Control

Product Version	Product	Author
2025.3.812	RadChat for WinForms	Dinko Krastev

Description

At the moment of writing this Knowledge Base article, the RadChat control does not expose such an event that will be triggered when a hyperlink is clicked. We can use a custom code to catch the moment when the user clicks a link before it is actually opened in the browser.

Solution

To intercept HTML links in RadChat, subclass the control and override its OnMouseDown method. Check if the clicked element is a hyperlink, then handle it accordingly.

Steps to Implement

1. Create a custom class inheriting from RadChat.
2. Override the OnMouseDown method to detect clicked links.
3. Use ElementTree.GetElementAtPoint to identify the element under the mouse.
4. Implement a helper method to verify if the mouse is over a link.
5. Replace the default RadChat control with the customized one in your Form.Designer.cs file.

Example Code

Below is the complete implementation:

public class MyRadChat : RadChat
{
    protected override void OnMouseDown(MouseEventArgs e)
    {
        var element = this.ElementTree.GetElementAtPoint(e.Location);
        if (element != null && element is ChatMessageBubbleElement chatMessageBubbleElement)
        {
            string[] numLines = chatMessageBubbleElement.Text.Split('\n');

            FormattedText formattedTextLink = IsMouseOverBlock(element, e, chatMessageBubbleElement.TextBlock.Lines);
            if (formattedTextLink != null)
            {
                var link = formattedTextLink.Link;
                return;
            }
            else
            {
                base.OnMouseDown(e);
            }
        }
        base.OnMouseDown(e);
    }

    FormattedText IsMouseOverBlock(object sender, MouseEventArgs e, List<TextLine> lines)
    {
        RadElement element = sender as RadElement;
        Debug.Assert(element != null, "Element is not RadElement");
        Point elementAtPoint = element.PointFromControl(e.Location);
        int linesCount = lines.Count();
        for (int i = 0; i < linesCount; ++i)
        {
            TextLine textLine = lines[i];
            int textLineCount = textLine.List.Count;
            for (int j = 0; j < textLineCount; ++j)
            {
                FormattedText formattedText = textLine.List[j];
                if (!string.IsNullOrEmpty(formattedText.Link) && formattedText.DrawingRectangle.Contains(elementAtPoint))
                {
                    return formattedText;//found link under mouse
                }
            }
        }

        return null;//notfound
    }
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadChat).FullName;
        }
    }
}

With this subclass, you can intercept links and customize their behavior, such as downloading content or displaying it in a custom viewer.

See Also

• RadChat Overview
• HTML-like Text Formatting