Merge pull request #812 from telerik/new-kb-chat-intercept-html-links-7e401019300049c98e7d100d84e56d3c

Added new kb article chat-intercept-html-links

Author: nade7o

knowledge-base/chat-intercept-html-links.md

@@ -0,0 +1,99 @@
+---
+title: Intercepting HTML Link Click in RadChat Control
+description: Learn how to intercept when HTML links are clicked in the RadChat control in UI for WinForms
+type: how-to
+page_title: Intercepting HTML Link Click in RadChat Control
+meta_title: Intercepting HTML Link Click in RadChat Control
+slug: chat-intercept-html-links
+tags: chat, radchat, link interception, html links, click events
+res_type: kb
+ticketid: 1701502
+---
+
+|Product Version|Product|Author|
+|----|----|----|
+|2025.3.812|RadChat for WinForms|[Dinko Krastev](https://www.telerik.com/blogs/author/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:
+
+````C#
+
+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](https://docs.telerik.com/devtools/winforms/controls/chat/overview)
+* [HTML-like Text Formatting](https://docs.telerik.com/devtools/winforms/telerik-presentation-framework/html-like-text-formatting)
+