How to clone Control event handlers at run time?

Question

I want to duplicate a control like a Button, TextBox, etc. But I don't know how I can copy event handler methods (like Click) to the new control.

I have the following code now:

var btn2 = new Button();  
btn2.Text = btn1.Text;
btn2.size = btn1.size;
// ...
btn2.Click ??? btn1.Click

Is there any other way to duplicate a control?

Answer 1

To clone all events of any WinForms control:

var eventsField = typeof(Component).GetField("events", BindingFlags.NonPublic | BindingFlags.Instance);
var eventHandlerList = eventsField.GetValue(button1);
eventsField.SetValue(button2, eventHandlerList);

Answer 2

You just need to add the event handler method for the new button control. C# uses the += operator to do this. So you could simply write:

btn2.Click += btn1_Click

Alternatively, a somewhat more powerful approach is to use reflection. Of particular use here would be the EventInfo.AddEventHandler method.

Answer 3

If you're simply looking to duplicate the HTML element that will eventually render (including attached event handlers), you can use below extension method to output a copy of the HTML.

/// <summary>
/// Render Control to HTML as string
/// </summary>
public static string Render(this System.Web.UI.Control control)
{
    var sb = new StringBuilder();
    System.IO.StringWriter stWriter = new System.IO.StringWriter(sb);
    System.Web.UI.HtmlTextWriter htmlWriter = new System.Web.UI.HtmlTextWriter(stWriter);
    control.RenderControl(htmlWriter);
    return sb.ToString();
}

Then you can use it to out put a copy in the aspx markup like this:

<%= btn1.Render() %>

If you want to modify, say, the text on the copy, you could do a string Replace on the Rendered html, or you could set the Text on the original button, and reset it after the Render call in the asx, i.e.:

<% btn1.Text = "Text for original button"; %>