Libgdx, button onclick event crashes

Question

I'm trying to create an android game using libgdx with a Titlescreen, you just press start and your game startes. However I'm having difficulty trying to get these buttons to work. The title-screen works, but as soon as I press 'start game' the game crashes with the error:

Exception in thread "LWJGL Application" java.lang.NullPointerException at com.dinab.onepiecev2.TitleScreen1ドル.clicked(TitleScreen.java:47) at com.badlogic.gdx.scenes.scene2d.utils.ClickListener.touchUp(ClickListener.java:88) at com.badlogic.gdx.scenes.scene2d.InputListener.handle(InputListener.java:59) at com.badlogic.gdx.scenes.scene2d.Stage.touchUp(Stage.java:351) at com.badlogic.gdx.backends.lwjgl.LwjglInput.processEvents(LwjglInput.java:360) at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:221) at com.badlogic.gdx.backends.lwjgl.LwjglApplication1ドル.run(LwjglApplication.java:128)

I don't understand what I'm doing wrong and whether the problem is in my TitleScreen.java or in my GameScreen.java

These are my codes:

Main class

public class Onepiecev2 extends Game {
 static public Skin gameSkin;
 public void create () {
 gameSkin = new Skin(Gdx.files.internal("skin/glassy-ui.json"));
 this.setScreen(new TitleScreen(this));
 }
 public void render () {
 super.render();
 }
 public void dispose () {
 }
}

TitleScreen

public class TitleScreen implements Screen {
 Stage stage;
 Game game;
 SpriteBatch batch;
 Texture img;
 TextureRegion mainBackground;
 public TitleScreen(Game aGame){
 batch = new SpriteBatch();
 img = new Texture("start_screen.jpg");
 mainBackground = new TextureRegion(img, 0, 0, 1920, 1080);
 stage = new Stage(new ScreenViewport());
 Gdx.input.setInputProcessor(stage);
 Skin mySkin = new Skin(Gdx.files.internal("skin/glassy-ui.json"));
 Button start_btn = new TextButton("START GAME", mySkin);
 start_btn.setSize(Constantes.screenWidth/4, Constantes.screenHeight/12);
 start_btn.setPosition(Constantes.col_width*3,Constantes.row_height/3);
 start_btn.addListener( new ClickListener() {
 @Override
 public void clicked(InputEvent event, float x, float y) {
 game.setScreen( new GameScreen(game) );
 }
 } );
 stage.addActor(start_btn);
 }
 @Override
 public void show() {
 Gdx.input.setInputProcessor(stage);
 }
 @Override
 public void render(float delta) {
 Gdx.gl.glClearColor(1, 1, 1, 1);
 Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
 batch.begin();
 batch.draw(mainBackground, 0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
 batch.end();
 stage.act();
 stage.draw();
 }
 @Override
 public void resize(int width, int height) {
 }
 @Override
 public void pause() {
 }
 @Override
 public void resume() {
 }
 @Override
 public void hide() {
 }
 @Override
 public void dispose() {
 stage.dispose();
 batch.dispose();
 img.dispose();
 }
}

GameScreen

public class GameScreen implements Screen {
 Stage stage;
 Game game;
 SpriteBatch batch;
 Texture img;
 TextureRegion mainBackground;
 public GameScreen(Game aGame){
 batch = new SpriteBatch();
 img = new Texture("start_screen.jpg");
 mainBackground = new TextureRegion(img, 0, 0, 1920, 1080);
 stage = new Stage(new ScreenViewport());
 Gdx.input.setInputProcessor(stage);
 Skin mySkin = new Skin(Gdx.files.internal("skin/glassy-ui.json"));
 Button start_btn = new TextButton("GO BACK", mySkin);
 start_btn.setSize(Constantes.screenWidth/4, Constantes.screenHeight/12);
 start_btn.setPosition(Constantes.col_width*3,Constantes.row_height/3);
 start_btn.addListener( new ClickListener() {
 @Override
 public void clicked(InputEvent event, float x, float y) {
 game.setScreen( new TitleScreen(game));
 }
 } );
 stage.addActor(start_btn);
 }
 @Override
 public void show() {
 Gdx.input.setInputProcessor(stage);
 }
 @Override
 public void render(float delta) {
 Gdx.gl.glClearColor(1, 1, 1, 1);
 Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
 batch.begin();
 batch.draw(mainBackground, 0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
 batch.end();
 stage.act();
 stage.draw();
 }
 @Override
 public void resize(int width, int height) {
 }
 @Override
 public void pause() {
 }
 @Override
 public void resume() {
 }
 @Override
 public void hide() {
 }
 @Override
 public void dispose() {
 stage.dispose();
 batch.dispose();
 img.dispose();
 }
}

Answer 1

From the crash log, it looks like the problem is in your TitleScreen where you are adding a click listener. I am referring to the following line.

game.setScreen(new GameScreen(game));

Looks like the game object is not initialized before and hence you are getting a NullPointerException.

• stayutazen: Thank you!! After adding the line this.game = aGame; it worked!