NullPointerException with libgdx using the gdx render() method

Question

Started making a game. Here's some of my code.

package games.tribe.screens;

import games.tribe.model.World;
import games.tribe.view.WorldRenderer;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Screen;
import com.badlogic.gdx.graphics.GL10;

public class GameScreen implements Screen {

private World world;
private WorldRenderer renderer;

/** This was the bit I'd missed --------------------------------------**/
@Override
public void show() {
    world = new World();
    renderer = new WorldRenderer(world);
}
/**------------------------------------------------------------------**/

@Override
public void render(float delta) {
    Gdx.gl.glClearColor(0.1f, 0.1f, 0.1f, 1);
    Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
    renderer.render();
}

@Override
public void resize(int width, int height) {
    // TODO Auto-generated method stub


}

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

}

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

}

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

}

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

}

}

here's the WorldRenderer Class:

package games.tribe.view;

import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.glutils.ShapeRenderer;
import com.badlogic.gdx.graphics.glutils.ShapeRenderer.ShapeType;
import com.badlogic.gdx.math.Rectangle;

import games.tribe.model.Block;
import games.tribe.model.TribalHunter;
import games.tribe.model.World;

public class WorldRenderer {

private World world;
private OrthographicCamera cam;

/**for debug rendering**/
ShapeRenderer debugRenderer = new ShapeRenderer();

public WorldRenderer(World world) {
    this.world = world;
    this.cam = new OrthographicCamera(10, 7);
    this.cam.position.set(5, 3.5f, 0);
    this.cam.update();
}

public void render()  {
    //render blocks
    debugRenderer.setProjectionMatrix(cam.combined);
    debugRenderer.begin(ShapeType.Rectangle);
    for(Block block : world.getBlocks()) {
        Rectangle rect = block.getBounds();
        float x1 = block.getPosition().x + rect.x;
        float y1 = block.getPosition().y + rect.y;
        debugRenderer.setColor(new Color(1, 0, 0, 1));
        debugRenderer.rect(x1, y1, rect.width, rect.height);
    }
    //render hunter
    TribalHunter hunter = world.getHunter();
    Rectangle rect = hunter.getBounds();
    float x1 = hunter.getPosition().x + rect.x;
    float y1 = hunter.getPosition().y + rect.y;
    debugRenderer.setColor(new Color(0, 1, 0, 1));
    debugRenderer.rect(x1, y1, rect.width, rect.height);
    debugRenderer.end();

}
}

This is the exception I'm getting when I run it as a desktop application:

Exception in thread "LWJGL Application" java.lang.NullPointerException
at games.tribe.screens.GameScreen.render(GameScreen.java:19)
at com.badlogic.gdx.Game.render(Game.java:46)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:202)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:131)
AL lib: ReleaseALC: 1 device not closed

Line 46 of gdx.Game.render is this method:

@Override
public void render () {
    if (screen != null) screen.render(Gdx.graphics.getDeltaTime());
}

Any help will be appreciated

Thanks in advance

Answer 1

In the GameScreen's render() method, has the renderer been initialized? That could be causing the problem if it hasn't.

Edit: The problem you're having, according to the top two lines of the error, is a NullPointerException on line 19 of the class GameScreen. The NullPointerException only occurs when an object is used for some action when the object itself is null because it likely hasn't been initialized.

Line 19 of the GameScreen is:

renderer.render();

...but the object renderer has not been initialized anywhere, so it is currently null which is the default. To avoid getting this error, you'll need to initialize the renderer object before you run that line of code. Perhaps with something like this:

@Override
public void render(float delta) {
    Gdx.gl.glClearColor(0.1f, 0.1f, 0.1f, 1);
    Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

    renderer = new WorldRenderer();
    renderer.render();
}

I am not familiar with libgdx, so I can't be sure that's exactly how a WorldRenderer is initialized, but you need to do something of the sort. I hope this helps.