我正在尝试使用 XNA 编写一个非常基本的自上而下的 2D 游戏，我已经到了尝试将草纹理添加到游戏中然后将这些纹理绘制到屏幕底部的部分。
但是，我在 Level.cs 类的第 32 行收到“NullReferenceException was Unhandled”错误。由于我只是 XNA 的新手，而 C# 的新手（相比之下），我无法终生解决这个问题。
更新 1：感谢 mcmonkey4eva，该错误已解决。但是，我的代码现在在我的 TestLevel 类 (Level.cs) 的 Draw() 方法中停止。该错误仍然是“NullReferenceException was Unhandled”错误，并且方法与它们的方法有些不同。
有人知道我在这里做错了什么吗？
这是我更新的 Level.cs 类：
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;
}
}
这是我更新的 Game1.cs 类：
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 GroundTile 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.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);
}
}
}