NullReferenceException was unhandled - not sure what's null

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.开发者_JAVA技巧
        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?

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.

This is a general answer for this kind of issue.

Run your code in the debugger. When it stops due to the unhandled null reference, hover your mouse over each item in the code line it stopped on. It should say, "null" for the one that is null. If your tooltips aren't working, click each item and use QuickWatch (Shift+F9) to display the value.

verts is probably null when trying to access verts.Length ? Check with the debugger by setting the breakpoint there and inspecting yourself.

I can assume that when it accessing verts.Length verts is null. But why you can not add Debug.WriteLine() outputs to see what exactly happens, or simply put a break point or Debugger.Break() call?

I would venture to guess that verts is null, this is based on the initialization.

In addition to all posts here, make sure that you enable exception handling in VS:

Choose "Common language runtime exceptions" check box and most likely VS will lead you on exact line where you got a problem.

EDIT

You can find it in VS menu: Debug-> Exceptions.

Hope this helps.

Regards.