AS3:如果在超级类中更改属性,我该如何触发事件？

Question

我在Sprite中有一个TextField,我总是希望TextField的alpha等于sprite的alpha.我如何订阅Sprite中所做的更改？我想我需要解决一些PropertychangeEvent,但我看不到sprite支持这个开箱即用？

class TextWidget extends Sprite{  
  private var textfield:TextField;    
  public function TextWidget(){  
    textfield = new TextField();  
    textfield.alpha = this.alpha;  //does'n help  
    addChild(textField);  
??  
  this.addEventListener(PropertyChangeEvent.PROPERTY_CHANGE, updateAlpha);  
??  
  }
  private function updateAlpha(event:PropertychangeEvent):void{  
    textfield.alpha = this.alpha;  
  }  
}  

Answer 1

一种方法是创建精灵的派生类并覆盖alpha属性

/**
 * ...
 * @author Andrew Rea
 */
public class CustomSprite extends Sprite
{

    public static const ALPHA_CHANGED:String = "ALPHA_CHANGED";

    public function CustomSprite() 
    {

    }

    override public function get alpha():Number { return super.alpha; }

    override public function set alpha(value:Number):void 
    {
        super.alpha = value;

        dispatchEvent(new Event(CustomSprite.ALPHA_CHANGED));
    }
}

另一种方法是只要在命中父精灵的alpha设置器时设置文本字段alpha,如上所示,只是没有事件.

安德鲁