1120：访问未定义的属性playWithTouch

Question

我认为我的代码没问题，但由于一些奇怪的原因，它无法正常工作。 我是这个AS3的新手，但我尽力让它发挥作用。

package {
  import flash.display.MovieClip;
  import flash.display.Stage;
  import flash.display.NativeMenu;
  import flash.display.NativeMenuItem;
  import flash.display.NativeWindow;
  import flash.events.MouseEvent;
  import flash.events.KeyboardEvent;
  import flash.events.AccelerometerEvent;
  import flash.events.TimerEvent;
  import flash.ui.Keyboard;
  import flash.ui.Multitouch;
  import flash.ui.MultitouchInputMode;
  import flash.system.System;
  import flash.desktop.SystemIdleMode;
  import flash.sensors.Accelerometer;
  import flash.utils.Timer;


  public class Shooter extends MovieClip {
    private var welcomeScreenMC: Welcome = new Welcome();
    public function Shooter() {
      // constructor code
      stage.addChild(welcomeScreenMC);
      welcomeScreenMC.x = stage.stageWidth / 2;
      welcomeScreenMC.y = stage.stageHeight / 2;
      welcomeScreenMC.buttonMC.addEventListener(MouseEvent.CLICK, playWithTouch);
    }
  }
}