c# - XNA - 当前上下文中不存在名称 'ball'

Question

因为我是 XNA 的新手，所以我正在开发一个乒乓球游戏，但我遇到了一个问题......我有 3 个类，"Game1.cs"、"Ball.cs" 和 "GreenPaddle.cs"。

GreenPaddle.cs 包含Rectangle gpRect、Texture2D gPtexture、Vector2 position。

我有运动等等，在球类中我有一个相交 bool 值。但是当我尝试在 game1.cs 中初始化它时，我得到了错误。以下是类(class):

GreenPaddle.cs:

public class GreenPaddle
{
    Texture2D gPtexture;
    public Vector2 position;
    public Rectangle gpRect;
    public Vector2 origin;
    public int speed = 2;

    public GreenPaddle()
    {

    }

    public void LoadContent(ContentManager Content)
    {
        gPtexture = Content.Load<Texture2D>("greenpaddle");
        position = new Vector2(20, 200);
        gpRect = new Rectangle((int)position.X, (int)position.Y,
            gPtexture.Width, gPtexture.Height);
    }

    public void Update(GameTime gameTime)
    {
        KeyboardState keyState = Keyboard.GetState();

        //Movement
        PaddleMovement();

        //Border Collision
        isCollidingWithBorders();
      }

    public void Draw(SpriteBatch spriteBatch)
    {
        spriteBatch.Draw(gPtexture, position, gpRect, Color.LawnGreen);
    }
    public Boolean isCollidingWithBorders()
    {
        if (position.Y < 83 && gpRect.Y < 83)
        {
            position.Y = 83;
            gpRect.Y = 83;
            return true;
        }

        if (position.Y > 400 && gpRect.Y > 400)
        {
            position.Y = 400;
            gpRect.Y = 400;
            return true;
        }

        else { return false; }

    }

    public void PaddleMovement()
    {
        KeyboardState keyState = Keyboard.GetState();
        if (keyState.IsKeyDown(Keys.W))
        {
            position.Y -= speed;
            gpRect.Y -= speed;
        }
        if (keyState.IsKeyDown(Keys.S))
        {
            position.Y += speed;
            gpRect.Y += speed;
        }
    }
}

球.cs:

public class Ball
{
    GreenPaddle gPaddle;


    Texture2D ballTexture;
    Vector2 ballPosition;
    Rectangle ballRect;
    int speed = 2;
    bool movingUp, movingLeft;

    public Ball(GreenPaddle paddle)
    {
        this.gPaddle = paddle;
        movingLeft = true;
        movingUp = true;
    }

    public void LoadContent(ContentManager Content)
    {
        ballTexture = Content.Load<Texture2D>("ball");
        ballPosition = new Vector2(380, 225);
        ballRect = new Rectangle((int)ballPosition.X, (int)ballPosition.Y,
            ballTexture.Width, ballTexture.Height);

    }

    public void Update(GameTime gameTime)
    {
        BallMovement();

    }

    public void Draw(SpriteBatch spriteBatch)
    {
        spriteBatch.Draw(ballTexture, ballPosition, ballRect, Color.White);
    }

    public void BallMovement()
    {
        if (movingUp) { ballPosition.Y -= speed; }
        if (!movingUp) { ballPosition.Y += speed; }
        if (movingLeft) { ballPosition.X -= speed; }
        if (!movingLeft) { ballPosition.X += speed; }

        if (ballRect.Intersects(gPaddle.gpRect))
            movingLeft = !movingLeft;
                movingUp = !movingUp;

        if (ballPosition.Y < 85)
        {
            movingUp = false;
        }
    }
}

游戏1.cs:

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

    GreenPaddle gPaddle = new GreenPaddle();


    Texture2D BackGround;

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
        graphics.PreferredBackBufferHeight = 500;
    }

    protected override void Initialize()
    {

    Ball ball = new Ball(gPaddle);
        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);

        BackGround = Content.Load<Texture2D>("pongBG");
        gPaddle.LoadContent(Content);
        //ball.LoadContent(Content);
    }

    /// <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();

        gPaddle.Update(gameTime);
        ball.Update(gameTime);//Error Line

        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();
        spriteBatch.Draw(BackGround, new Vector2(0f, 0f), Color.White);
        gPaddle.Draw(spriteBatch);
        ball.Draw(spriteBatch);//Error Line
        spriteBatch.End();

        base.Draw(gameTime);
    }
}

就是这样，我不知道如何处理初始化部分:/

Answer 1

仔细看看你是如何初始化你的球的，你在方法的范围内声明它(大括号之间)。这意味着您无法在其他任何地方访问它，而您正试图在 Update 和 Draw 方法中进行访问。

protected override void Initialize()
{
    Ball ball = new Ball(gPaddle);
    base.Initialize();
}

此外，一旦函数结束，您的 Ball 对象就会被删除。

这可以通过将 Ball ball 放入你的类范围内来解决，这样它对类的所有成员都可用，如下所示:

Ball ball;  //In the class scope

protected override void Initialize()
{
    ball = new Ball(gPaddle);
    base.Initialize();
}

如果您不熟悉作用域，请查看 this文章(MSDN 上没什么好东西)