C# ArgumentNullException was unhandled (SpriteBatch.Draw)

Question

I am actually a new student in XNA, finding this library very interesting, but I still lack some knowledge to go further as I felt on a issue I can't fix on my own :(

The spriteBatch.Draw() method says my texture is null, however I have loaded it in a Resources.cs class and passed the texture in MainMenu.cs, so I don't really know where the problem resides, if anybody could help me about that I would be very thankful !

Resources.cs

    class Resources
{
    public static Texture2D pixel;
    public static Texture2D startButton, loadButton, quitButton;

    public static SpriteFont consoleFont;

    public static void LoadContent(ContentManager Content)
    {
        pixel = Content.Load<Texture2D>("Pixel");
        consoleFont = Content.Load<SpriteFont>("Console");

        // UI Ressources :
        startButton = Content.Load<Texture2D>("UI/StartButton");
        loadButton = Content.Load<Texture2D>("UI/LoadButton");
        quitButton = Content.Load<Texture2D>("UI/QuitButton");
    }
}

MainMenu.cs

    class MainMenu
{
    // Fields
    List<Button> buttons = new List<Button>();

    // Constructors
    public MainMenu()
    {
        this.buttons.Add(new Button(new Vector2(480, 132), 256, 48, Resources.startButton));
        this.buttons.Add(new Button(new Vector2(480, 212), 256, 48, Resources.loadButton));
        this.buttons.Add(new Button(new Vector2(480, 292), 256, 48, Resources.quitButton));
    }

    // Methods

    // Update
    public void Update()
    {
    }

    // Draw
    public void Draw(SpriteBatch spriteBatch)
    {
        foreach (Button button in buttons)
        {
            button.Draw(spriteBatch);
        }
    }
}

Button.cs

    class Button : UIElement
{
    int width, height;
    Texture2D texture;

    public Button()
    {
    }

    public Button(Vector2 b_position, int b_width, int b_height, Texture2D b_texture)
    {
        this.position = b_position;
        this.width = b_width;
        this.height = b_height;
        this.texture = b_texture;
    }

    public void Update()
    {
    }

    public void Draw(SpriteBatch spriteBatch)
    {
        spriteBatch.Draw(texture, position, Color.White);
    }
}

Answer 1

While I do not see your Game class my first assumption is that your never calling the public static void LoadContent(ContentManager Content) method inside your Resources class. Since this function is instantiating your textures perhaps this isn't being called.

Answer 2

Thank you for your reply ! Indeed I forgot to include the Game class, is this the right way to call the resources ?

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

    MainMenu mainMenu;

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

        this.IsMouseVisible = true;

        mainMenu = new MainMenu();
    }

    protected override void Initialize()
    {
        // TODO: Add your initialization logic here

        base.Initialize();
    }

    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        // TODO: use this.Content to load your game content here
        Resources.LoadContent(Content);
    }

    protected override void UnloadContent()
    {
        // TODO: Unload any non ContentManager content here
    }

    protected override void Update(GameTime gameTime)
    {
        // Allows the game to exit
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();

        // TODO: Add your update logic here
        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);

        // TODO: Add your drawing code here
        spriteBatch.Begin();
        mainMenu.Draw(spriteBatch);
        spriteBatch.End();
        base.Draw(gameTime);
    }
}

Answer 3

Simple realy
You just have to know the calling order of functions of Game1. First, Game1 constructor is called. That's where you've put mainMenu = new MainMenu();. After that go Initialize, Load and so on. You have to move mainMenu = new MainMenu(); from Game1 constructor to Load function, after the Resources.LoadContent(Content);, so the resources can be loaded before they are used in MainMenu. Your Game1.cs code should look like this:

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

    MainMenu mainMenu;

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

        this.IsMouseVisible = true;
    }

    protected override void Initialize()
    {
        // TODO: Add your initialization logic here

        base.Initialize();
    }

    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        // TODO: use this.Content to load your game content here
        Resources.LoadContent(Content);
        mainMenu = new MainMenu();
    }

    protected override void UnloadContent()
    {
        // TODO: Unload any non ContentManager content here
    }

    protected override void Update(GameTime gameTime)
    {
        // Allows the game to exit
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();

        // TODO: Add your update logic here
        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);

        // TODO: Add your drawing code here
        spriteBatch.Begin();
        mainMenu.Draw(spriteBatch);
        spriteBatch.End();
        base.Draw(gameTime);
    }
}