空引用异常

Question

“你调用的对象是空的。”

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;

namespace XNAdev
{
    class Sprite
    {
        //The size of the Sprite
        public Rectangle Size;

        //Used to size the Sprite up or down from the original image
        public float Scale = 1.0f;

        //The current position of the Sprite
        public Vector2 Position = new Vector2(115, 0);
        //The texture object used when drawing the sprite
        private Texture2D mSpriteTexture;

        //Load the texture for the sprite using the Content Pipeline
        public void LoadContent(ContentManager theContentManager, string theAssetName)
        {
            mSpriteTexture = theContentManager.Load<Texture2D>(theAssetName);
            Size = new Rectangle(0, 0, (int)(mSpriteTexture.Width * Scale), (int)(mSpriteTexture.Height * Scale));
        }

        //Draw the sprite to the screen
        public void Draw(SpriteBatch theSpriteBatch)
        {
            theSpriteBatch.Draw(mSpriteTexture, Position,
                new Rectangle(0, 0, mSpriteTexture.Width, mSpriteTexture.Height), Color.White,
                0.0f, Vector2.Zero, Scale, SpriteEffects.None, 0);

        }    
    }
}

我对 C# 很陌生，所以任何帮助都会很棒。

我不知道我的错误是什么。

---

namespace XNAdev
{

    public class Game1 : Microsoft.Xna.Framework.Game
    {
        GraphicsDeviceManager graphics;
        SpriteBatch spriteBatch;
        Sprite mSprite;
        Sprite mSpriteTwo;
        Sprite mBackgroundOne;
        Sprite mBackgroundTwo;
        Sprite mBackgroundThree;
        Sprite mBackgroundFour;
        Sprite mBackgroundFive;





        public Game1()
        {           

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

        protected override void Initialize()
        {
            mSprite = new Sprite();
            mSpriteTwo = new Sprite();

            mBackgroundOne = new Sprite();
            mBackgroundOne.Scale = 2.0f;

            mBackgroundTwo = new Sprite();
            mBackgroundTwo.Scale = 2.0f;

            mBackgroundThree = new Sprite();
            mBackgroundThree.Scale = 2.0f;

            mBackgroundFour = new Sprite();
            mBackgroundFour.Scale = 2.0f;

            mBackgroundFive = new Sprite();
            mBackgroundFive.Scale = 2.0f;

            base.Initialize();
        }

        protected override void LoadContent()
        { 
            spriteBatch = new SpriteBatch(GraphicsDevice);

            mSprite.Position = new Vector2(125, 245);

            mSpriteTwo.LoadContent(this.Content, "SquareGuy");
            mSpriteTwo.Position.X = 300;
            mSpriteTwo.Position.Y = 300;

            mBackgroundOne.LoadContent(this.Content, "Background01");
            mBackgroundOne.Position = new Vector2(0, 0);            

            mBackgroundTwo.LoadContent(this.Content, "Background02");
            mBackgroundTwo.Position = new Vector2(mBackgroundOne.Position.X + mBackgroundOne.Size.Width, 0);

            mBackgroundThree.LoadContent(this.Content, "Background03");
            mBackgroundThree.Position = new Vector2(mBackgroundTwo.Position.X + mBackgroundTwo.Size.Width, 0);

            mBackgroundFour.LoadContent(this.Content, "Background04");
            mBackgroundFour.Position = new Vector2(mBackgroundThree.Position.X + mBackgroundThree.Size.Width, 0);

            mBackgroundFive.LoadContent(this.Content, "Background05");
            mBackgroundFive.Position = new Vector2(mBackgroundFour.Position.X + mBackgroundFour.Size.Width, 0);            
        }

        protected override void UnloadContent()
        {

        }


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

            if (mBackgroundOne.Position.X < -mBackgroundOne.Size.Width)
            {
                mBackgroundOne.Position.X = mBackgroundFive.Position.X + mBackgroundFive.Size.Width;
            }

            if (mBackgroundTwo.Position.X < -mBackgroundTwo.Size.Width)
            {
                mBackgroundTwo.Position.X = mBackgroundOne.Position.X + mBackgroundOne.Size.Width;
            }

            if (mBackgroundThree.Position.X < -mBackgroundThree.Size.Width)
            {
                mBackgroundThree.Position.X = mBackgroundTwo.Position.X + mBackgroundTwo.Size.Width;
            }

            if (mBackgroundFour.Position.X < -mBackgroundFour.Size.Width)
            {
                mBackgroundFour.Position.X = mBackgroundThree.Position.X + mBackgroundThree.Size.Width;
            }

            if (mBackgroundFive.Position.X < -mBackgroundFive.Size.Width)
            {
                mBackgroundFive.Position.X = mBackgroundFour.Position.X + mBackgroundFour.Size.Width;
            }

            Vector2 aDirection = new Vector2(-1, 0);
            Vector2 aSpeed = new Vector2(160, 0);

            mBackgroundOne.Position += aDirection * aSpeed * (float)gameTime.ElapsedGameTime.TotalSeconds;
            mBackgroundTwo.Position += aDirection * aSpeed * (float)gameTime.ElapsedGameTime.TotalSeconds;
            mBackgroundThree.Position += aDirection * aSpeed * (float)gameTime.ElapsedGameTime.TotalSeconds;
            mBackgroundFour.Position += aDirection * aSpeed * (float)gameTime.ElapsedGameTime.TotalSeconds;            
            mBackgroundFive.Position += aDirection * aSpeed * (float)gameTime.ElapsedGameTime.TotalSeconds;            
        }

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

            spriteBatch.Begin();

            mBackgroundOne.Draw(this.spriteBatch);
            mBackgroundTwo.Draw(this.spriteBatch);
            mBackgroundThree.Draw(this.spriteBatch);
            mBackgroundFour.Draw(this.spriteBatch);
            mBackgroundFive.Draw(this.spriteBatch);

            mSprite.Draw(this.spriteBatch);
            mSpriteTwo.Draw(this.spriteBatch);
            spriteBatch.End();

            base.Draw(gameTime);
        }
    }
}

这就是剩下的代码

Answer 1

1. 查找如何将 Visual Studio 设置为在出现异常时中断。
2. 了解如何使用调试器，以便您可以单步执行代码以查看错误发生的位置。

Answer 2

我仔细查看了它并设法使用验证让它工作，如果您正在绘制的精灵具有空引用（无纹理），它将忽略它并继续绘制其他所有内容。

将 Sprite.cs 中的 Draw() 方法更改为：

//Draw the sprite to the screen
public void Draw(SpriteBatch theSpriteBatch)
{
    if (mSpriteTexture != null)
    {
        theSpriteBatch.Draw(mSpriteTexture, Position,
            new Rectangle(0, 0, mSpriteTexture.Width, mSpriteTexture.Height), Color.White,
            0.0f, Vector2.Zero, Scale, SpriteEffects.None, 0);
    }
}

出现问题是因为您从未为“Sprite mSprite;”提供纹理，而只提供了位置。

快速片段：

protected override void LoadContent()
{
    spriteBatch = new SpriteBatch(GraphicsDevice);

    mSprite.Position = new Vector2(125, 245);

    mSpriteTwo.LoadContent(this.Content, "SquareGuy");
    mSpriteTwo.Position.X = 300;
    mSpriteTwo.Position.Y = 300;

正如您所看到的，您只为 mSprite 指定了 125,245 的位置，只需为它分配一个纹理，就像您为其余精灵分配的纹理一样，它就可以正常工作。

不过，在分配纹理后，您不需要从 Draw() 方法中删除 if(mSpriteTexture != null) ，如果您不这样做，则意味着您不会注意到某些内容没有正确分配，如果您稍后要调试其他内容，可能会很痛苦。

Answer 3

也许您

 mSpriteTexture = theContentManager.Load<Texture2D>(theAssetName);
 if (mSpriteTexture != null)
     Size = new Rectangle(0, 0, (int)(mSpriteTexture.Width * Scale), (int)(mSpriteTexture.Height * Scale));

也应该在 Draw 函数中检查 And 。

Answer 4

此错误意味着在未实例化对象的情况下尝试访问对象的字段或方法之一。

对于您的代码来说，这似乎发生在对象 mSpriteTexture 上。

你应该在某个地方添加

mSpriteTexture = new Texture2D();

，但我无法仅用这段代码来判断在哪里。