Question

I’m working on building an icosphere, and I’ve gotten as far as the draw portion of the code, but I keep getting a NullReferenceException was unhandled error. I know which bt of code it’s pointing at, but I don;t know what’s actually wrong or how to fix it.

Here’s the class code:

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;

namespace Icosahedron_Test
{
/// <summary>
/// This is the main type for your game
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;

    Camera camera;

    VertexPositionColor[] verts;
    VertexBuffer vertexBuffer;

    BasicEffect effect;

    Matrix worldTranslation = Matrix.Identity;
    Matrix worldRotation = Matrix.Identity;

    int radius = 1; //planet radius
    int refinement = 2;  // number of times to refine surface
    TriXYZ[] vertices; // array containin vertex locations

    Icosahedron planet;

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
    }

    /// <summary>
    /// Allows the game to perform any initialization it needs to before starting to run.
    /// This is where it can query for any required services and load any non-graphic
    /// related content.  Calling base.Initialize will enumerate through any components
    /// and initialize them as well.
    /// </summary>
    protected override void Initialize()
    {
        camera = new Camera(this, new Vector3(0, 0, 5),
            Vector3.Zero, Vector3.Up);
        Components.Add(camera);


        planet = new Icosahedron(radius, refinement, vertices); // create the planet object ( the icosphere )
        vertices = planet.InitializeArray();  // fill the initial verticies list (TriXYZ[])

        //Here is where you will get the world radius and number of time to refine. For now, use constants

        vertices = planet.Refine(vertices, refinement);  // subdivide the triangles as many times as is specified by refinement variable

        // at this point, I should be able to move on to draw and create the list for drawing the triangles of the icosphere

        base.Initialize();
    }

    /// <summary>
    /// LoadContent will be called once per game and is the place to load
    /// all of your content.
    /// </summary>
    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        //Initialize Verticies
        VertexPositionColor[] verts;

        verts = planet.BuildList(vertices);

        //set vertex data in vertexBuffer
        vertexBuffer = new VertexBuffer(GraphicsDevice, typeof(VertexPositionColor),
            verts.Length, BufferUsage.None);
        vertexBuffer.SetData(verts);

        //Initialize BAsic effect
        effect = new BasicEffect(GraphicsDevice);
    }

    /// <summary>
    /// UnloadContent will be called once per game and is the place to unload
    /// all content.
    /// </summary>
    protected override void UnloadContent()
    {
        // TODO: Unload any non ContentManager content here
    }

    /// <summary>
    /// Allows the game to run logic such as updating the world,
    /// checking for collisions, gathering input, and playing audio.
    /// </summary>
    /// <param name="gameTime">Provides a snapshot of timing values.</param>
    protected override void Update(GameTime gameTime)
    {
        // Allows the game to exit
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();

        //Translation
        KeyboardState keyboardState = Keyboard.GetState();
        if (keyboardState.IsKeyDown(Keys.Left))
            worldTranslation *= Matrix.CreateTranslation(-.01f, 0, 0);
        if (keyboardState.IsKeyDown(Keys.Right))
            worldTranslation *= Matrix.CreateTranslation(.01f, 0, 0);
        if (keyboardState.IsKeyDown(Keys.Up))
            worldTranslation *= Matrix.CreateTranslation(0, .01f, 0);
        if (keyboardState.IsKeyDown(Keys.Down))
            worldTranslation *= Matrix.CreateTranslation(0, -.01f, 0);
        //Rotation
        worldRotation *= Matrix.CreateFromYawPitchRoll(
            MathHelper.PiOver4 / 60,
            0,
            0);


        base.Update(gameTime);
    }

    /// <summary>
    /// This is called when the game should draw itself.
    /// </summary>
    /// <param name="gameTime">Provides a snapshot of timing values.</param>
    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);
        GraphicsDevice.SetVertexBuffer(vertexBuffer);

        //Set object and camera info
        effect.World = worldRotation * worldTranslation * worldRotation;
        effect.View = camera.view;
        effect.Projection = camera.projection;
        effect.VertexColorEnabled = true;

        //Begin effect and draw for pass
        foreach (EffectPass pass in effect.CurrentTechnique.Passes)
        {
            pass.Apply();

            GraphicsDevice.DrawUserPrimitives<VertexPositionColor>
                (PrimitiveType.TriangleList, verts, 0, (verts.Length/3));
        }

        base.Draw(gameTime);
    }
}
}

The portion of code it’s pointing at is this:

GraphicsDevice.DrawUserPrimitives<VertexPositionColor>
    (PrimitiveType.TriangleList, verts, 0, (verts.Length/3));

Does anyone see what’s causing this problem?

Answer 1

verts is null because the variable is never getting assigned. Your LoadContent() method creates a verts inside of its scope, which ignores the one that is a member of your class.