Question

Can anyone please help. Im following a tutorial on drawing primitives from the MSDN found here.

I am trying to re-factor the code a small bit and to that end I have created a class called MyPrimitives in which I have placed all of the code from the tutorial. Then from e.g. Game11 Initialize() I can just call myPrimitive.Initialize() etc.

But I get a NullReferenceException at this line of code in MyPrimitives CreateVertexBuffer() method:

vertexBuffer = new VertexBuffer(
            graphics.GraphicsDevice,
            vertexDeclaration,
            number_of_vertices,
            BufferUsage.None
            );

And CreateVertexBuffer() is called from MyPrimitives Initialize() method like so:

public void Initialize()
    {
        CreateVertexBuffer();
    }

And THIS Initialize() is called from Game1 Initialize() like so:

protected override void Initialize()
    {
        myPrimitiveDrawer = new MyPrimitiveDrawer();

        myPrimitiveDrawer.Initialize();

        base.Initialize();
    }

I know the problem is cause I have not set my graphis [GraphicsDeviceManager graphics] to an instance of an object, but how do I actually do this?
I have tried:

public void Initialize()
    {
        graphics = new GraphicsDeviceManager(this);  // Tried this
        CreateVertexBuffer();
    }

But that just gives an error of invalid arguments.

Does anyone have any suggestion please?

Answer 1

Start with your main game class and make it extend Microsoft.Xna.Framework.Game

public class Game : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;

    protected override void Initialize()
    {
            graphics = new GraphicsDeviceManager(this);  
            base.Initialize();
    }
}

Then you just need to make sure that all of your classes uses the same GraphicsDeviceManager when the project expand.