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F# and Gtk.Builder (formerly Glade)
f#

Hi,

I'm trying to write a simple F# GUI with Gtk.Builder.

Basing on the C# solution found here: [link:lists.ximian.com]

So here is the C# code (tested, works):
---
using System;

using Gtk;

public class MyWindow

{
[Builder.Object]
Window window1 = null;

static void Main (string [] args)

{

new MyWindow (args);

}

public MyWindow (string [] args)

{

Application.Init ();
Builder builder = new Builder ("builder.ui");

builder.Autoconnect (this);

window1.ShowAll ();

Application.Run ();

}

}
---
Now this is what I have for F#
---
open System
open Gtk

type MyWindow (args : string[]) as this = class
[<Builder.Object>]
let window1 : Window = null

let _ =
Application.Init()
let builder = new Builder("builder.ui")
builder.Autoconnect(this)
window1.ShowAll()
Application.Run()
end

[<EntryPoint>]
let main(args : string[]) =
let mywindow = new MyWindow(args)
0
---
Even though it compiles, I get an error:
Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object
at Gtk.Widget.ShowAll () [0x00000] in <filename unknown>:0
at Test+MyWindow..ctor (System.String[] args) [0x00000] in <filename unknown>:0
at Test.main (System.String[] args) [0x00000] in <filename unknown>:0

I guess the problem is either the line with the "window1" declaration or the "Autoconnect" function.
There is a snipet from the "old" Glade solution in this forum, but that didn't really help me: [link:cs.hubfs.net]

Can somebody point me in the right direction?

Thanks,
Adam

.

One thing to try may be to apply STAThreadAttribute. See e.g.

[link:lorgonblog.wordpress.com]

for an example.

By on 10/12/2010 4:34 PM ()

Thanks, but that didn't make any difference.

By on 10/12/2010 4:47 PM ()

Next guess, try changing "let _ = " to "do".

By on 10/12/2010 8:11 PM ()

Still the same Exception.

By on 10/12/2010 8:14 PM ()

Ohhh, I bet window1 is being optimized away by the compiler as a field, so whatever magic on the Builder.Object attribute or something is unused.

Try adding e.g.

member this.Whatever() = window1

or some member that will force realization of window1 as a class field rather than just a local variable inside the constructor.

By on 10/12/2010 8:19 PM ()

Thanks so much, that was the problem!

By on 10/12/2010 8:31 PM ()

Hurray!

(Lest anyone think this is an implementation artifact of the compiler, it is actually part of the language spec, section 8.6.2

“let” and “do” Declarations in Primary Constructors

[link:research.microsoft.com]

)

By on 10/12/2010 8:41 PM ()

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