AS3：無法訪問空對象引用的屬性

Question

我想用動畫片段跟蹤鼠標的X位置。

我迄今所做的：

public class LuckyHitBeta extends MovieClip { 


    var ballReady:ballReady_mc; 



private function liveIcon():void { 
      ballReady=new ballReady_mc(); 
      addChild(ballReady); 
      ballReady.y=1; 
     } 

private function onEnterFrm(e:Event):void 
    {   
     ballReady.x=mouseX; 

    } 

} 

運行時錯誤：

TypeError: Error #1009: Cannot access a property or method of a null object reference. 
at LuckyHitBeta/onEnterFrm() 

Answer 1

我沒有看到你調用函數liveIcon()。看起來enterFrame事件發生在ballready初始化之前。

Answer 2

我想它的意思ballReady是NULL

我會做類似

private function onEnterFrm(e:Event):void 
{   
    if (ballReady) { 
     ballReady.x=mouseX; 
    } 
}