[Gtk-sharp-list] Problem with event handlers: GtkSharp.voidObjectSignal

[Marc Eilens]

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Hi guys,

just installed GtkSharp and had a look at some examples I got on a CD from a
magazine.
Running the example code attached (I simplified the original code to a
minimum) results in following exception:

>>>
Unhandled Exception: System.NullReferenceException: A null value was found
where an object instance was required
in (unmanaged) 06 GtkSharp.voidObjectSignal:g_signal_connect_data
(intptr,string,GtkSharp.voidObjectDelegate,int,intptr,int)
in <0x00004> 06 GtkSharp.voidObjectSignal:g_signal_connect_data
(intptr,string,GtkSharp.voidObjectDelegate,int,intptr,int)
in <0x000ba> 00 GtkSharp.voidObjectSignal:.ctor
(GLib.Object,intptr,string,System.Delegate,System.Type)
in <0x00095> 00 Gtk.Button:add_Clicked (System.EventHandler)
in <0x000af> 00 .Example:CreateGui ()
in <0x00041> 00 .Sample:Main ()
<<<

I'm totally new to GTK and quite new to C# but for the C# side, I think I
don't do anything forbidden. And for the GTK side, if I leave out the code
adding the event handler to the button, everything is ok.
In the docs, I found a similar example (Hello 2nd try from the go-mono
tutorial) which works. The difference to my code fragment is that the GUI is
set up in the Main method and not in a method of another class.

What am I doing wrong?

FYI: I'm using mono 0.22, gtk-sharp-0.8 and gtk+-2.2.1 on a SuSE Linux 8.1
system.

Thanks in advance,
Marc

>>>
using Gtk;
using GtkSharp;
using System;

class Example
{
	Window win;
	Statusbar statusbar;

	public void CreateGui()
	{
		win = new Window ("Example");
 		Button button = new Button("OK");
                button.Clicked += new EventHandler(ButtonClicked);
	        win.Add(button);
                win.ShowAll ();
	}

    static void ButtonClicked(object sender, EventArgs e)
    {
    	Console.WriteLine("button clicked");
    }
}

class Sample {

	public static void Main()
	{
		Application.Init ();
		Example example = new Example();
		example.CreateGui();
		Application.Run();
	}
}
<<<
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