Setting up a draw class giving exceptions

Question

I'm currently trying to set up a class to draw tiles for me in different shapes, but it's currently giving me a hard time, as it's giving me nullreferenceobject errors in my secondary class. My Game class:

public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;

        Tile tl = new Tile();

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

            graphics.PreferredBackBufferWidth = 1280;
            graphics.PreferredBackBufferHeight = 960;
            //graphics.IsFullScreen = true;


        }

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

           base.Initialize();
        }

        protected override void LoadContent()
        {
            spriteBatch = new SpriteBatch(GraphicsDevice);
            Content.RootDirectory = "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);
        }

        /// <summary>
        /// This is called when the game should draw itself.
        /// </summary>
        /// <param name="gameTime">Provides a snapshot of timing values.</param>
        /// 

        inputForm iForm = new inputForm();

        bool[,] centerPiece = new bool[,] { { false, true, false }, { true, true, true }, { false, true, false } };
        bool[,] cornerPiece = new bool[,] { { false, true, false }, { true, true, false }, { false, false, false } };
        bool[,] stairPiece = new bool[,] { { false, true, false }, { true, true, true }, { false, false, false } };
        bool[,] straightPiece = new bool[,] { { false, true, false }, { false, true, false }, { false, true, false } };
        protected override void Draw(GameTime gameTime)
        {
            GraphicsDevice.Clear(Color.White);   

            // Draw the sprite.
            spriteBatch.Begin(SpriteSortMode.BackToFront, BlendState.AlphaBlend);

            //Draw centerPiece
            tl.centerPiece(spriteBatch, centerPiece);

            spriteBatch.End();

            base.Draw(gameTime);

            //iForm.Show();
        }
    }

And my tile class:

 public class Tile : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        public float spacing = 32f;
        public Texture2D squareTex;

        public Vector2 IMGCenter()
        {
            Vector2 imageCenter = new Vector2(4 / 2f, 4 / 2f);
            return imageCenter;
        }

        public Vector2 screenView()
        {
            Viewport viewport = GraphicsDevice.Viewport;
            Vector2 screenCenter = new Vector2(viewport.Width / 2f, viewport.Height / 2f);
            return screenCenter;
        }

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

            squareTex = Content.Load<Texture2D>("square"); 
        }

        public void centerPiece(SpriteBatch batch, bool[,] squareCombo)
        {
            for (int x = 0; x < squareCombo.GetLength(0); x++)
            {
                for (int y = 0; y < squareCombo.GetLength(1); y++)
                {
                    if (squareCombo[x, y] == true)
                    {
                        Vector2 offset = new Vector2(x, y) * spacing;
                        Vector2 position = IMGCenter() + offset;

                        batch.Draw(squareTex, screenView(), null, Color.White, 0f, position, 1f, SpriteEffects.None, 0f);
                    }
                }
            }
        }
    }

EDIT2: My current error:

An unhandled exception of type 'Microsoft.Xna.Framework.Content.ContentLoadException' occured in Microsoft.Xna.Framework.Graphics.dll. 
Additional information: Error loading 'square' GraphicsDevice component not found.

Where do you actually set squareTex? And where do you load the texture? — Felsir, Oct 25 at 9:16
@Felsir My bad, been modifying my code. Edited my post, I do it in the Tile() constructor. Getting a graphics component not found atm. — Jon Dier, Oct 25 at 9:24
Please post the stack-trace of the NullReferenceException so we can see where exactly it gets thrown. — Philipp, Oct 25 at 9:27
@Philipp changed my code(also in the post), getting the error regarding the program not able to find my "square" now, based on graphics device missing. Adding the full exception in a sec — Jon Dier, Oct 25 at 9:28
The problem is more how you applied the monogame/XNA framework, the stacktrace is not relevant judging the code. — Felsir, Oct 25 at 9:33

Felsir · Accepted Answer · 2016-10-25 09:50:31Z

up vote 0 down vote accepted

The issue is how you try to load your content. This way your texture is never correctly initialized. There are a couple of ways to solve your issue.

First, note there is a Content Manager (it is the Content variable in the main class). This is not a global scope variable- you either need to pass it to other classes that need to load content, or you need to create a new Content Manager in the other class.

The easiest way to solve your issue is this:

Change your Tile constructor to this:

public Tile(ContentManager content)
    {
        squareTex = content.Load<Texture2D>("square"); 
    }

And pass the contentmanager when you create your tile:

Tile tl = new Tile(Content);

Since you need an initialized Content Manager for this, I suggest to create your tile in the LoadContent() method.

The Content Manager is quite smart, it won't load the content it already knows. So even if you create a new tile, the Content Manager will reference the same texture. Still there are other options that may help you in the long run.

Create an 'Assets' class, where you load all the content your game needs. Reference these textures in your object Draw methods.
Pass textures on creation of your object. This makes your objects reusable with a graphic variation (example a player's spaceship class could be instantiated with a red texture for player 1 and a blue texture for player 2).

answered Oct 25 at 9:50

Felsir

2,8822725

I tried creating my Tile in the LoadContent(), but I'm initializing the centerPiece function in Draw(). So the tl in Draw() doesn't exist in current context, as the creation of the Tile class doesn't work as a global variable. – Jon Dier Oct 25 at 9:56

Tried adding the: tl.centerPiece(spriteBatch, centerPiece); to LoadContent() as well, but that still gives me a "square" not found exception – Jon Dier Oct 25 at 10:00

Did you add square to the game content? – Felsir Oct 25 at 10:04

Yes. I made the code work and draw originally solely in the Game1 class, I simply wanted to split the program up in two classes, so I could use tile seperately and repeatedly. I almost used the exact same code for Tile that I used for Game1 – Jon Dier Oct 25 at 10:05

Fixed the tile error by creating an empty variable and changing its content in LoadContent(). Still getting the "square" error not found though. – Jon Dier Oct 25 at 10:18

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Steve H · Answer 2 · 2016-10-26 00:03:27Z

Your class structure is not typical. There is no reason to have your Tile class inherit a Game class. This instantiates 2 Game objects. No need for that. Drop the inheritance. You only need one Game object. If you need to exchange data or use Game methods from the Tile class, provide the Tile class with a reference to the game class, but don't inherit from it.

Next, at the beginning of your Game class, declare a Tile object instead of "newing" one. Then "new" it in the load content class after the Game lass has had a chance to initialize its Graphics device & Content manager. Pass the Content Manager and Graphics Device to the Tile Class in a manner similar to how Felsir indicated.

Additional info: Your error is because it can't find the GrapicsDevice... not the content. The GraphicsDeviceManager you are creating in your Tile Class will not initiate unless a Game's Run() method is called. The Framework calls that internally for the main Game object but never for the Tile's inherited Game object which is the device being used to load... That's why your error is saying it can't find the GraphicsDevice, not the tile content.

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