“[AppName] 已停止”在我的物理设备中。 logcat 中的错误：java.lang.NullPointerException

Question

我一直在 android 工作室和 libgdx 开发游戏，每当我运行在我的物理设备上玩游戏时，它都会显示“[AppName] 已停止”。

我已经检查了我使用的图像的名称（拼写、大小写），除此之外我不知道是什么问题。

这是我在 logcat 中收到的错误：

10-06 12:01:51.055 21591-21627/com.jpfalmazan.ninjaassault E/AndroidRuntime: FATAL EXCEPTION: GLThread 2891
                                                                             java.lang.NullPointerException
                                                                                 at com.jpfalmazan.ninjaassault.GameScreens.MenuScreen.<init>(MenuScreen.java:23)
                                                                                 at com.jpfalmazan.ninjaassault.NinjaAssault.create(NinjaAssault.java:19)
                                                                                 at com.badlogic.gdx.backends.android.AndroidGraphics.onSurfaceChanged(AndroidGraphics.java:275)
                                                                                 at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1505)
                                                                                 at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1240)

这是我的游戏代码：

package com.jpfalmazan.ninjaassault;

import com.badlogic.gdx.Game;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.jpfalmazan.ninjaassault.GameScreens.MenuScreen;


public class NinjaAssault extends Game {
    public SpriteBatch batch;
    Texture img;

    @Override
    public void create () {
        batch = new SpriteBatch();
        this.setScreen(new MenuScreen(this));   ////This is the "NinjaAssault.java:19 " error shown in logcat 
    }

    @Override
    public void render () {
        super.render();
        Gdx.gl.glClearColor(1,0,0,1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
        batch.begin();
    }

    @Override
    public void dispose () {
        batch.dispose();
        img.dispose();
    }
}

这是我在 MenuScreen 中的代码 class:

package com.jpfalmazan.ninjaassault.GameScreens;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Screen;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.jpfalmazan.ninjaassault.NinjaAssault;

public class MenuScreen implements Screen{
    NinjaAssault game;
    public MenuScreen (NinjaAssault game){
        this.game = game;
    }
    public SpriteBatch batch;
    public Texture background;
    public Texture title;
    public Texture playButtonINACTIVE;
    public Texture playButtonACTIVE;

    public float screenWidth = Gdx.graphics.getWidth();
    public float screenHeight = Gdx.graphics.getHeight();
    public float titleWidth = title.getWidth();  //This is the "MenuScreen.java:23" error shown in logcat 
    public float titleHeight = title.getHeight();
    public float xLimit1 = (float) ((screenWidth/2)-(titleWidth/2));
    public float xLimit2 = (float) ((screenWidth/2)+(titleWidth/2));
    public float yLimit1 = (float) ((screenHeight*.35));
    public float yLimit2 = (float) ((screenHeight*.35)+titleHeight);



    @Override
    public void show() {
        batch = new SpriteBatch();
        background = new Texture("BGYELL.png");
        title = new Texture ("BGASTRO.png");
        playButtonINACTIVE = new Texture("BTPLAY.png");
        playButtonACTIVE = new Texture("BTPLAYON.png");

    }

    @Override
    public void render(float delta) {
        Gdx.gl.glClearColor(1,0,0,1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
        game.batch.begin();
        game.batch.draw(background,0,0,screenWidth,screenHeight);
        if((Gdx.input.getX()> xLimit1 && Gdx.input.getX() < xLimit2) && (Gdx.input.getY() < yLimit2 && Gdx.input.getY() > yLimit1 ) ){
            game.batch.draw(playButtonACTIVE,(screenWidth/2)-(playButtonACTIVE.getWidth()/2), (float) (screenHeight*.35));
        }else  game.batch.draw(playButtonINACTIVE,(screenWidth/2)-(playButtonINACTIVE.getWidth()/2), (float) (screenHeight*.35));
        game.batch.draw(title,(screenWidth/2)-((float)(screenWidth*.8)/2), (float) (screenHeight*.65),(float)(screenWidth*.8) , (float) ((screenWidth*.8)*(titleHeight/titleWidth)));




        game.batch.end();
    }

    @Override
    public void resize(int width, int height) {

    }

    @Override
    public void pause() {

    }

    @Override
    public void resume() {

    }

    @Override
    public void hide() {

    }

    @Override
    public void dispose() {

    }
}

Answer 1

您尚未对 "title" 进行任何设置。你只是宣布它存在。标题在构造函数之后调用的 show() 中设置。你需要做

title = new Texture ("BGASTRO.png");

在尝试获取纹理高度之前。这也适用于所有其他变量，请确保在使用它们之前将它们设置为某些内容。

此外，您应该删除

 Gdx.gl.glClearColor(1,0,0,1);
 Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
 batch.begin();

来自 NinjaAssault 中的 render() class。这是不必要的，如果你打电话

batch.begin()

你需要打电话给

batch.end()

也是，但在这种情况下，它从未被使用过，所以根本不需要它。

“[AppName] 已停止”在我的物理设备中。 logcat 中的错误：java.lang.NullPointerException

"[AppName] has stopped" in my physical device. ERROR in logcat: java.lang.NullPointerException

java

android

nullpointerexception

libgdx

spritebatch