关于c＃：NullReferenceException未处理 – 不明白为什么

NullReferenceException was Unhandled - No idea why

我正在尝试用XNA编写一个非常基本的自顶向下的二维游戏，我已经开始尝试在游戏中添加草地纹理，然后将这些纹理绘制到屏幕的底部。

但是，我的level.cs类的第32行上出现了"NullReferenceException was unmanaged"错误。因为我对XNA还只是个新手(相比之下)对C还比较陌生，所以我无法在我的生活中理解这一点。

更新1：感谢McMonkey4eva，该错误已解决。但是，我的代码现在在testlevel类(level.cs)的draw()方法期间停止。该错误仍然是一个"NullReferenceException was unmanaged"错误，并且方法与以前有点不同。

有人知道我做错了什么吗？

这是我更新的level.cs类：

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

namespace First.Level
{
class TestLevel
{
//An array of groundtiles that will be set to grass, lava, etc
public GroundTile[,] groundlevel;

//Width/Height of the Level
int width, height;

Grass grass;

public TestLevel(int width, int height, ContentManager myContent)
{
content = myContent;
//I input my screen dimensions as my level size
this.width = width;
this.height = height;

groundlevel = new GroundTile[width, height];

grass = new Grass(content.Load<Texture2D>(@"Images\GroundTiles"));
}

//Drawing the grass near the bottom of the screen
public void generateGround()
{
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x += 32)
{
if (y == (height - 100))
{
if (groundlevel[x, y] == null)
{
groundlevel[x, y] = grass;
}

}
}
}

}

public void draw(GameTime gameTime, SpriteBatch spriteBatch)
{
foreach(GroundTile ground in groundlevel)
{
ground.Draw(gameTime, spriteBatch); //Here's where the error is
}
}

public static ContentManager Content
{
get { return content; }
}
static ContentManager content;
}
}

以下是我更新的game1.cs类：

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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;
using First.Entity;
using First.Tiles;
using First.Level;

namespace First
{
/// <summary>
/// This is the main type for your game
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{

const int SCREEN_WIDTH = 600;
const int SCREEN_HEIGHT = 400;

GraphicsDeviceManager graphics;
SpriteBatch spriteBatch;

TestLevel level;

UserControlledSprite Lancer;
Texture2D lancerTexture;
Vector2 position = new Vector2(200, 200);
Point frameSize = new Point(32, 48);
int collisionOffset = 0;
Point currentFrame = new Point(0, 0);
Point sheetSize = new Point(4, 4);
Point spriteToUse = new Point(0, 0);
Vector2 speed = new Vector2(2, 2);
int millisecondsPerFrame = 500;

Rectangle clientBounds;

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()
{
// TODO: Add your initialization logic here

clientBounds = graphics.GraphicsDevice.Viewport.Bounds;
clientBounds.Width = SCREEN_WIDTH;
clientBounds.Height = SCREEN_HEIGHT;

this.IsMouseVisible = true;

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);

Content.RootDirectory ="Content";

level = new TestLevel(SCREEN_WIDTH, SCREEN_HEIGHT, Content);
level.generateGround();

lancerTexture = Content.Load<Texture2D>(@"Images\Lancer");
Lancer = new UserControlledSprite(lancerTexture, position, frameSize, collisionOffset,
currentFrame, sheetSize, spriteToUse, speed, millisecondsPerFrame);
}

/// <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();

Lancer.Update(gameTime, clientBounds);

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);

spriteBatch.Begin();
Lancer.Draw(gameTime, spriteBatch);
level.draw(gameTime, spriteBatch);
spriteBatch.End();

base.Draw(gameTime);
}
}
}

这是我的grass.cs课程：

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

namespace First.Level
{
class TestLevel
{
//An array of groundtiles that will be set to grass, lava, etc
public GroundTile[,] groundlevel;

//Width/Height of the Level
int width, height;

Grass grass;

public TestLevel(int width, int height, ContentManager myContent)
{
content = myContent;
//I input my screen dimensions as my level size
this.width = width;
this.height = height;

groundlevel = new GroundTile[width, height];

grass = new Grass(content.Load<Texture2D>(@"Images\GroundTiles"));
}

//Drawing the grass near the bottom of the screen
public void generateGround()
{
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x += 32)
{
if (y == (height - 100))
{
if (groundlevel[x, y] == null)
{
groundlevel[x, y] = grass;
}

}
}
}

}

public void draw(GameTime gameTime, SpriteBatch spriteBatch)
{
foreach(GroundTile ground in groundlevel)
{
ground.Draw(gameTime, spriteBatch);
}
}

public static ContentManager Content
{
get { return content; }
}
static ContentManager content;
}
}

以防万一，这也是我的地砖课：

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

namespace First.Tiles
{
class GroundTile
{

//public GroundTile grass = new Grass(content.Load<Texture2D>(@"Images\GroundTiles"));

// frameSize needs to be modular, for the objects above walking-ground level

public Texture2D texture;
protected Point frameSize;
public Point frame;
public Vector2 position;
int collisionOffset;
protected Point sheetSize = new Point(9, 19);

public GroundTile(Texture2D tiles, Point frame, Point frameSize, int collisionOffset)
{
this.frame = frame;
this.frameSize = frameSize;
this.collisionOffset = collisionOffset;

this.texture = tiles;
}

//Collision Detection, incase of water or something
public Rectangle collisionRect
{
get
{
return new Rectangle(
(int)position.X + collisionOffset,
(int)position.Y + collisionOffset,
frameSize.X - (collisionOffset * 2),
frameSize.Y - (collisionOffset * 2));
}
}

//Not really used, but just in case
public bool collidesWith(GroundTile tile, Sprite sprite)
{
if (sprite.collisionRect.Intersects(collisionRect))
{
sprite.position -= sprite.direction;
}

return false;
}

public static ContentManager Content
{
get { return content; }
}
static ContentManager content;

public GraphicsDevice Graphicsdevice
{
get { return graphicsDevice; }
}
GraphicsDevice graphicsDevice;

public virtual void Draw(GameTime gameTime, SpriteBatch spriteBatch)
{
spriteBatch.Draw(texture,
position,
new Rectangle(frame.X * frameSize.X,
frame.Y * frameSize.Y,
frameSize.X, frameSize.Y),
Color.White, 0, Vector2.Zero,
1f, SpriteEffects.None, 0);
}

}
}

在设置之前，您正在访问Content，或者，更确切地说，您从未设置过它。

变化

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public TestLevel(int width, int height)
{
//I input my screen dimensions as my level size

到

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public TestLevel(int width, int height, ContentManager myContent)
{
content = myContent;
//I input my screen dimensions as my level size

然后在创建TestLevel对象时添加content参数(我从game1.cs中假设)(注意：在[在loadcontent方法中]创建content对象之后，一定要创建TestLevel！)

编辑：

对于新问题：

你没有定义数组的内容，除了一层草…

线

1	ground.Draw(gameTime, spriteBatch);

改为

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if (ground != null)
{
ground.Draw(gameTime, spriteBatch);
}

但你也应该确保这片土地实际上充满了内容…具体来说，数组中每个点的新平铺对象，不仅是一条线，而且不是每个位置的相同"草地"实例。

我不想冒犯你，但你在处理一些基本的错误。您可以查阅并遵循一些基本的C教程。