title: LibGDX Listener in Actor in Stage doesn't work
body: <p>The input listener doesn't fire in the Actor even if the Actor was already added to the stage and the input processor was already set to the stage. What could be the problem here?
  Inside GameScreen (extends Screen) class:</p>
  
  
  
  <pre class="lang-java prettyprint-override"><code>public GameScreen(Game game) {
     this.game = game;
     stage = new Stage(800, 480, true);
     number = new Number();
     stage.addActor(number);
  }
  
  public void show() {
     Gdx.input.setInputProcessor(stage);
  }
  
  public void render(float delta) {
     Gdx.gl.glClearColor(0, 0, 0, 1);
     Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
     stage.act(delta);
     stage.draw();
  }
  </code></pre>
  
  <p>Constructor of Number:</p>
  
  <pre class="lang-java prettyprint-override"><code>public Number() {
          addListener(new InputListener() {
              public boolean touchDown(InputEvent event, float x, float y, int pointer, int button) {
                  System.out.println("touch down");
                  return true;
              }
  
              public void touchUp(InputEvent event, float x, float y, int pointer, int button) {
                  System.out.println("touch up");
              }
  
              public boolean mouseMoved(InputEvent event, float x, float y) {
                  System.out.println("mouse moved");
                  return true;
              }
          });
  }
  </code></pre>