Question

我正在构建一个Flex应用程序，我遇到了检测变量是否已初始化的问题。请观察此简化代码示例：

<fx:Script>
  <![CDATA[
    private var pageObject:* = null; //Yes the "*" data type is needed ;)

  //Fired by the application elseware
    private function constructMenu(e:ResultEvent):void {
      if (this.pageObject != null) {
        //This block never runs...

        // The pageObject will be null when the application
        // first runs, so skip this first time around.
        // However... this method will be called multiple
        // times. Since FoodMenu() is a display object
        // and is instantiated below, all subsequent calls
        // to this method will require us to remove the old
        // display object before adding a new one.
      } else {
        // This block always runs...
      }

      setTimeout(function():void {
        this.pageObject = new FoodMenu(); //Should now be not-null!!!

        //Do more stuff with the FoodMenu() and add to the main application
      }, 1000);
    }
  ]]>
</fx:Script>

根据给定的代码示例和注释，有人可以解释为什么this.pageObject始终注册为非null，无论调用constructMenu()方法的次数是多少次{{1} class是实例化的吗？

感谢您的时间。

编辑：请求的完整MXML

FoodMenu()

Answer 1

我看到的一个可能的问题是使用这段代码：

setTimeout(function():void {
   this.pageObject = new FoodMenu(); //Should now be not-null!!!
   //Do more stuff with the FoodMenu() and add to the main application
}, 1000);

“this”指针指向闭包中的其他东西（可能是全局对象）。

请尝试以下方法为自己寻找：

trace(this);
setTimeout(function():void {
    trace(this);
},1000);

Flash实例变量始终为空？

1 个答案: