Question

我正在尝试在游戏调整大小时更新游戏的视口，但是当我开始游戏时，我得到java.lang.NullPointerException：

Exception in thread "LWJGL Application" java.lang.NullPointerException
at com.badlogic.gdx.utils.viewport.Viewport.apply(Viewport.java:49)
at com.badlogic.gdx.utils.viewport.ExtendViewport.update(ExtendViewport.java:90)
at com.badlogic.gdx.utils.viewport.Viewport.update(Viewport.java:57)
at me.chrisjosten.testgame.screens.MainScreen.resize(MainScreen.java:82)
at com.badlogic.gdx.Game.setScreen(Game.java:62)
at me.chrisjosten.testgame.create(MainScreen.java:13)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:136)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:114)

在实现Screen的类中，我在resize方法中发生了异常的地方，代码如下：

@Override
public void resize(int w, int h) {
    viewport.update(w, h);
}

其中视口是在类的构造函数中创建的ExtendViewport。我已经尝试将它放在show方法中，但后来我得到了相同的结果。

班级的完整代码：

package me.chrisjosten.testgame.screens;

import me.chrisjosten.testgame.MyGame;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Screen;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.g2d.BitmapFont;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.math.Vector3;
import com.badlogic.gdx.utils.viewport.ExtendViewport;
import com.badlogic.gdx.utils.viewport.FillViewport;
import com.badlogic.gdx.utils.viewport.Viewport;

public class MainScreen implements Screen{

    private MyGame game;
    private BitmapFont font;
    private SpriteBatch batch;

    private OrthographicCamera camera;
    private Viewport viewport;
    private boolean goingUp = false;
    private float alpha = 1;

    private int gameWidth = 100;
    private int gameHeight = 100;

    private int screenWidth;
    private int screenHeight;

    public MainScreen(MyGame g) {
        game = g;
        System.out.println("screen created");
    }

    @Override
    public void show() {
        System.out.println("show");
        font = new BitmapFont(Gdx.files.internal("fonts/monospace.fnt"));
        font.setColor(1, 1, 1, 1);

        batch = new SpriteBatch();

        camera = new OrthographicCamera(Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        camera.translate(gameWidth / 2,  gameHeight / 2);
        viewport = new ExtendViewport(gameWidth, gameHeight, camera);
    }

    @Override
    public void render(float delta) {
        camera.update();
        Gdx.gl.glClearColor(0, 0, 0, 1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

        if (goingUp) {
            font.setColor(1, 1, 1, alpha);
            alpha += 0.025;
        } else {
            font.setColor(1, 1, 1, alpha);
            alpha -= 0.025;
        }
        if (alpha <= 0) {
            goingUp = true;
            alpha = 0;
        } else if (alpha >= 1) {
            goingUp = false;
            alpha = 1;
        }
        batch.setProjectionMatrix(camera.combined);
        batch.begin();
        String press = "Press start";
        font.draw(batch, press, gameWidth / 2 - font.getBounds(press).width / 2, 1);
        batch.end();

    }

    @Override
    public void resize(int w, int h) {
        viewport.update(w, h);
    }

    @Override
    public void pause() {
        // TODO Auto-generated method stub

    }

    @Override
    public void resume() {
        // TODO Auto-generated method stub

    }

    @Override
    public void hide() {
        // TODO Auto-generated method stub

    }

    @Override
    public void dispose() {
        // TODO Auto-generated method stub
        font.dispose();
    }

}

有谁知道我做错了什么？

Answer 1

通过将代码从show方法移到构造函数，它可以工作。

尝试更新视口时Libgdx NullPointerException

1 个答案: