NullPointerException？不知道爲什麼。 LIBGDX

Question

我一直在39行，這是 modelBatch.begin(cam);

我不知道，爲什麼它這樣得到一個NullPointerException。如果你注意到了，請告訴我。我一整天都在努力解決這個問題。我對android開發很陌生，很容易犯下愚蠢的錯誤。感謝您的幫助。

public class Loading implements Screen { 

private boolean AP; 
private Chemistry chemistry; 
public PerspectiveCamera cam; 
public ModelBatch modelBatch; 
public Model model; 
public ModelInstance instance; 
public Lights lights; 

public Loading(boolean AP, Chemistry chemistry) { 
    this.AP = AP; 
    this.chemistry = chemistry; 
} 

@Override 
public void render(float delta) { 
    Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), 
      Gdx.graphics.getHeight()); 
    Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); 

    modelBatch.begin(cam); 
    modelBatch.render(instance, lights); 
    modelBatch.end(); 
} 

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

@Override 
public void show() { 
      modelBatch = new ModelBatch(); 
    lights = new Lights(); 
    lights.ambientLight.set(0.4f, 0.4f, 0.4f, 1f); 
    lights.add(new DirectionalLight().set(0.8f, 0.8f, 0.8f, -1f, -0.8f, 
      -0.2f)); 

    cam = new PerspectiveCamera(70, Gdx.graphics.getWidth(), 
      Gdx.graphics.getHeight()); 
    cam.position.set(10f, 10f, 10f); 
    cam.lookAt(0, 0, 0); 
    cam.near = 0.1f; 
    cam.far = 300f; 
    cam.update(); 

    ModelBuilder modelBuilder = new ModelBuilder(); 
    model = modelBuilder.createBox(5f, 5f, 5f, 
      new Material(ColorAttribute.createDiffuse(Color.GREEN)), 
      Usage.Position | Usage.Normal); 

    instance = new ModelInstance(model); 

} 
     ... 
} 

Answer 1

移動這對你的構造：

 modelBatch = new ModelBatch(); 
lights = new Lights(); 
lights.ambientLight.set(0.4f, 0.4f, 0.4f, 1f); 
lights.add(new DirectionalLight().set(0.8f, 0.8f, 0.8f, -1f, -0.8f, 
     -0.2f)); 

cam = new PerspectiveCamera(70, Gdx.graphics.getWidth(), 
     Gdx.graphics.getHeight()); 
cam.position.set(10f, 10f, 10f); 
cam.lookAt(0, 0, 0); 
cam.near = 0.1f; 
cam.far = 300f; 
cam.update(); 

ModelBuilder modelBuilder = new ModelBuilder(); 
model = modelBuilder.createBox(5f, 5f, 5f, 
     new Material(ColorAttribute.createDiffuse(Color.GREEN)), 
     Usage.Position | Usage.Normal); 

instance = new ModelInstance(model); 

，如：

public Loading(boolean AP, Chemistry chemistry) { 
    this.AP = AP; 
    this.chemistry = chemistry; 
    //here 
}