How do I move an object with an accelerometer in libGDX?

Question

I am working on a game which uses the accelerometer to move an object called "plane". I know how to add an accelerometer, but I can't get the plane to move.

package com.wyvern.pp.states;


import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Input;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.wyvern.pp.PPlane;


public class PlayState extends State{
    private boolean peripheralAvailable;

    private Texture walls;
    private Texture bg;
    private Texture plane;

    public PlayState(GameStateManager gsm) {
        super(gsm);

        walls = new Texture("walls.png");
        bg = new Texture("bg.png");
        plane = new Texture("plane_left.png");

        cam.setToOrtho(true);

        peripheralAvailable = Gdx.input.isPeripheralAvailable(Input.Peripheral.Accelerometer);
    }

    @Override
    protected void handleInput() {

    }

    @Override
    public void update(float dt) {
        handleInput();

        float xRot;
        if(peripheralAvailable) {
            xRot = Gdx.input.getAccelerometerX();
        }
    }

    @Override
    public void render(SpriteBatch sb) {
        sb.begin();
        sb.draw(bg, 0, 0, PPlane.WIDTH, PPlane.HEIGHT);
        sb.draw(walls, 0, 0);
        sb.draw(plane, xRot, 15 ); // gives an error 
        sb.draw(walls, PPlane.WIDTH - walls.getWidth(), 0);
        sb.end();
    }

    @Override
    public void dispose() {

    }
}

How do I get the plane to move left and right on the X axis?

Answer 1

It gives an error because it doesn't know what xRot is. In your method declaration of update(), you define float xRot;. Because you defined it within the declaration, it only exists within that declaration—it's a local variable.

To fix the error, just move the variable's declaration (float xRot;) up to where all the other fields (variables declared at the top of the class) are, like this:

package com.wyvern.pp.states;


import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.Input;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.wyvern.pp.PPlane;


public class PlayState extends State{
    private boolean peripheralAvailable;

    private Texture walls;
    private Texture bg;
    private Texture plane;

    private float xRot; // here

    public PlayState(GameStateManager gsm) {
        super(gsm);

        walls = new Texture("walls.png");
        bg = new Texture("bg.png");
        plane = new Texture("plane_left.png");

        cam.setToOrtho(true);

        peripheralAvailable = Gdx.input.isPeripheralAvailable(Input.Peripheral.Accelerometer);
    }

    @Override
    protected void handleInput() {

    }

    @Override
    public void update(float dt) {
        handleInput();

        // no "float xRot" here

        if(peripheralAvailable) {
            xRot = Gdx.input.getAccelerometerX();
        }
    }

    @Override
    public void render(SpriteBatch sb) {
        sb.begin();
        sb.draw(bg, 0, 0, PPlane.WIDTH, PPlane.HEIGHT);
        sb.draw(walls, 0, 0);
        sb.draw(plane, xRot, 15 ); // no longer gives an error 
        sb.draw(walls, PPlane.WIDTH - walls.getWidth(), 0);
        sb.end();
    }

    @Override
    public void dispose() {

    }
}