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我想从一个名为“ChoiceBtn”的类中向舞台添加一个事件监听器。

我收到错误“1009：无法访问空对象引用的属性或方法”。我知道这是因为该对象尚未实例化。

这是我的代码：

我的主要文档代码：

    import ChoiceBtn;

var op1:ChoiceBtn = new ChoiceBtn("display meee", answer, 1, "a)", "4.jpg");
op1.x = 250;
op1.y = 60;
stage.addChild(op1);

我的班级文件：

package  {

import AnswerEvent;
import flash.display.Loader;
import flash.display.Sprite;
import flash.display.SimpleButton;
import flash.events.*;
import flash.ui.Mouse;
import flash.text.TextField;
import flash.text.TextFormat;
import flash.net.URLRequest;
import flash.display.Stage;

public class ChoiceBtn extends Sprite{
    public var path:String;
    public var choiceText:String;
    public var choiceLabel:String;

    private var answer:Answer;
    private var choiceNum:uint;
    private var textFormat:TextFormat = new TextFormat();
    private var choiceLabelHwd:TextField = new TextField();
    private var choiceTextHwd:TextField = new TextField();
    private var boundingRect:Sprite = new Sprite;
    private var hitAreaWidth = 255;
    private var hitAreaHeight = 45;
    private var pic:Loader = new Loader;

    public function ChoiceBtn(choiceText:String, answer:Answer, choiceNum:uint, choiceLabel:String = "a)", picPath:String = null) {
        //path - must be the path to a picture
        //choiceText - the text to be displayed
        //choiceLabel - the prefix selector such as answers '1' or 'a)' etc.

        // constructor code
        this.answer = answer;
        this.choiceNum = choiceNum;
        this.choiceLabel = choiceLabel;
        this.choiceText = choiceText;

        //add childs
        addChild(this.choiceTextHwd);
        addChild(this.choiceLabelHwd);
        addChild(this.boundingRect);    //must be added last so is on top of everything else

        //add Listeners
        //stage.addEventListener(AnswerEvent.EVENT_ANSWERED, update); //doesn't work
        stage.addEventListener(AnswerEvent.EVENT_ANSWERED, this.update); //doesn't work either
    }

    public function update(e:Event):void {
        trace("in choice fired");
    }
}
}

我不明白为什么即使我this在函数之前使用它也不起作用。如何在此类构造函数代码中在舞台上创建事件侦听器并引用此类内的函数。

4

1 回答 1

1

Wait for the ADDED_TO_STAGE event to fire first:

public function ChoiceButton():void
{
    // your code.. etc..    
    addEventListener(Event.ADDED_TO_STAGE,addListeners);
}

private function addListeners(event:Event):void
{
    stage.addEventListener(AnswerEvent.EVENT_ANSWERED, update);             
}
于 2013-08-17T22:16:19.907 回答