Back to Questions
1.1k
views3
comments
0
score		+
-
F#, class, object and XNA
f#

Hello,

I'm trying to use F# and the XNA framework.

But I've got several problems. The first one is to make the real difference between "let" and "val" in an object.

Ca you give me some explanations ?

the second problem is:

I create a object (for example a camera) which inherit "Microsoft.Xna.Framework.GameComponent".

In my program, I use a "val" construction to declare my camera. It seems to works. But my problem is that my camera is visible, it's not an internal value of my object.

So I try to change "val" to "let"...but let value must be initialized. the problem is that I need to pass my "game" object to my camera...but the game object is in construction...

type Camera (game : Game, pos : Vector3, target : Vector3, up : Vector3) as this =
inherit Microsoft.Xna.Framework.GameComponent(game)

...

type Game1 () as this =
inherit Microsoft.Xna.Framework.Game ()

let mutable graphics: GraphicsDeviceManager = null
let mutable spriteBatch: SpriteBatch = null
let mutable bonhomme : Model = null

let mutable worldMatrix : Matrix = Matrix.Identity
let mutable viewMatrix : Matrix = Matrix.Identity
let mutable projMatrix : Matrix = Matrix.Identity

let mutable m_camera : Camera
let mutable m_waterPlane : DrawablePlane

do
graphics <- new GraphicsDeviceManager (this)
base.Content.RootDirectory <- @"Content"
m_camera <- new Camera(this, new Vector3(0.0f, 0.0f, 50.0f), Vector3.Zero, Vector3.Up)

Above, "this" isn't known.

So How can I do ?

Thanks,

Olivier

.Reply
Hide this comment

Hello,

Thanks a lot for your answer.

I modified my code and it looks better now without "val" !!!

Olivier

By on 2/18/2009 1:32 PM ()Reply
Hide this comment

I got around the same problem your having by using as and then. I forget the exact reason why you can't reference this in new. Check out my blog. I recently started my own gaming project with XNA in F#.

I posted code that works which is very similar to yours. Scroll down a bit on my blog and you will see the new constructor i use. I'd post it here but I'm having issues using this sites bbcode.

By on 2/17/2009 3:03 PM ()Reply
Hide this comment

My first piece of advice is to never use 'val' - always define an 'implicit'/'primary' constructor on your class.

In your code, since you must initialize let-bound variables, you could just initialize 'm_camera' to 'null' (or Unchecked.defaultof<Camera> if Camera is an F# type) in the let, and then re-assign in in the constructor body ('do' block) as you are.

You're right that you can't use 'this' before the 'do' starts, so you have to do the initialize-to-some-throwaway-value-(e.g. null)-and-then-re-assign.

Does that answer your question?

By on 2/17/2009 2:27 PM ()Reply

    Topic tags

    See all tags
    IntelliFactory Offices Copyright (c) 2011-2012 IntelliFactory. All rights reserved.
    Home | Products | Consulting | Trainings | Blogs | Jobs | Contact Us | Terms of Use | Privacy Policy | Cookie Policy     		Built with WebSharper

    Logging in...