“menuinterface.Menu.exit”从未分配给，并且始终具有其默认值 null“

Question

如何在另一个类中使用 Exit()？我想在 Intro 类中使用它，但我总是得到“menuinterface.Menu.exit”从未分配给，并且总是有其默认值 null“错误消息。怎么了？

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

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

    protected override void Initialize()
    {
        currentState = new Intro();
        base.Initialize();
    }

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

    protected override void Update(GameTime gameTime)
    {
        currentState.Update(gameTime);         
        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);
        spriteBatch.Begin();
        currentState.Render(spriteBatch);
        spriteBatch.End();

        base.Draw(gameTime);
    }
}

public interface IState
    {
        void Load(ContentManager content);
        void Update(GameTime gametime);
        void Render(SpriteBatch batch);
    }

public class Intro : IState
{
    private IState currentState;
    private Game1 exit;
    Texture2D introscreen;

    public void Load(ContentManager content)
    {
        introscreen = content.Load<Texture2D>("intro");
    }

    public void Update(GameTime gametime)
    {
        KeyboardState kbState = Keyboard.GetState();
        if (kbState.IsKeyDown(Keys.Space))
          currentState = new Menu();
        if (kbState.IsKeyDown(Keys.Escape))
            exit.Exit();
    }

    public void Render(SpriteBatch batch)
    {
        batch.Draw(introscreen, new Rectangle(0, 0, 1280, 720), Color.White);
    }
}

Answer 1

这是你的问题：

public class Intro : IState
{
    private IState currentState;
    private Game1 exit;
    Texture2D introscreen;

    public void Load(ContentManager content)
    {
        introscreen = content.Load<Texture2D>("intro");
    }

    public void Update(GameTime gametime)
    {
        KeyboardState kbState = Keyboard.GetState();
        if (kbState.IsKeyDown(Keys.Space))
          currentState = new Menu();
        if (kbState.IsKeyDown(Keys.Escape))
            exit.Exit(); // ---- this object does not exist
    }

    public void Render(SpriteBatch batch)
    {
        batch.Draw(introscreen, new Rectangle(0, 0, 1280, 720), Color.White);
    }
}

在这个类中，您声明了一个名为 exit 的对象，但从未分配过此值。您需要在使用对象之前对其进行实例化。在您的情况下，我会添加以下构造函数来解决您的问题。

public Intro(Game1 game)
{
    exit = game;
}

Answer 2

您没有为您的exit 对象分配任何内容，该对象似乎是Game 类型，所以这就是您收到此错误的原因。但是你为什么首先需要这个exit 对象呢？

如果你想在按下 Escape 后退出游戏，请使用Exit() 方法。它不需要您像在代码中那样使用它。就这么简单：

public class Game1 : Microsoft.Xna.Framework.Game
{
    // ...
    protected override void Update(GameTime gameTime)
    {            
        if (kbState.IsKeyDown(Keys.Escape))
            Exit();  

        base.Update(gameTime);
    }
    // ...
}