Question

我希望有人可以解释从超类访问变量的子类。

我发现子类只能访问在超类的构造函数中设置的变量。有没有办法解决这个问题？

package Character {

 import flash.display.MovieClip;

 public class Character extends MovieClip {
  protected var test_declared_early:String = "declared early";
  protected var test_declared_late:String;

  private var knight:Knight;

  public function Character() {
   // constructor code
  }

  public function init(_local_stage:Object){
   test_declared_late = "declared late";
   knight = new Knight("matt");
  }

 }

我尝试访问子类中的字符串，但只能得到一个：

package Character{

 public class Knight extends Character.Character {

  private var myName:String;

  public function Knight(local_name:String) {
   // constructor code
   myName = local_name;
   trace(super.test_declared_early); //this is not null
   trace(super.test_declared_late); //this is null
  }

 }

}

我的整个测试项目可以在这里找到： http://www.mediafire.com/?46zwpfo4h47cdaq

谢谢！

Answer 1

这里有几点需要注意，首先，在访问超类的属性时，您不需要这样做：

super.test_declared_early

而不仅仅是：

test_declared_early

其次，test_declared_late为null的原因是所有字符串的默认值为null。您尚未为其分配值！必须调用init，或者您需要手动设置它。

快乐的编码！

Answer 2

我几乎是肯定的，我在调用init后跟踪它。在这里我添加了一些跟踪，并显示我调用init的代码：

GameScreen类调用init：

package
{
    import flash.display.MovieClip;

    public class GameScreen extends MovieClip
    {

        public var docClass:Test;
        public function GameScreen(passed_class:Test)
        {
            // constructor code
            docClass = passed_class;
            trace("call init");
            _character.init(this);
        }
    }

}

角色等级：

package Character {

    import flash.display.MovieClip;

    public class Character extends MovieClip {
        protected var test_declared_early:String = "declared early";
        protected var test_declared_late:String;

        private var knight:Knight;

        public function Character() {
            // constructor code
        }

        public function init(_local_stage:Object){
            trace("setting late variable");
            test_declared_late = "declared late";
            trace("construct a knight");
            knight = new Knight("matt");
        }

    }

}

骑士子类：

package Character{

    public class Knight extends Character.Character {

        private var myName:String;

        public function Knight(local_name:String) {
            // constructor code
            myName = local_name;
            trace("in knight constructor, early= " + test_declared_early); //this is not null
            trace("in knight constructor, late= " +test_declared_late); //this is null
        }

    }

}

所有这些的输出是：

call init
setting late variable
construct a knight
in knight constructor, early= declared early
in knight constructor, late= null

也许我不理解你是什么，但它仍然看起来我在调用init并在我在子类中追踪它之前设置变量。

感谢您的帮助！

Answer 3

感谢您提示不需要超级。

但是，我没有说清楚，但程序的另一部分调用init：

在GameScreen类中：

_character.init(this);

在

之前设置跟踪

test_declared_late = "declared late";

显示它被调用。另外，如果没有调用init，代码将无法访问knight构造函数。

如果你有时间我会非常感激，如果你能查看来源 http://www.mediafire.com/?46zwpfo4h47cdaq

谢谢！

Answer 4

我真的建议您查看私有，受保护和公开的含义。我不会在这篇文章中写一本关于 OOP 的书，所以我知道你检查基础知识。

我将做什么我会给你一个关于如何使用和声明变量的样本。

class A
{
    private var _password:String;
    public var username:String;
    protected var serverURL:String;

    public function login():void
    {
         // some code
         callServerForLogin();
    }

    protected function callServerForLogin():void
    { 
        // some code
    }
 }

 class B extends A
 {
      public function B()
      {
           var parentPassword = super._password;  
           // FAILS because private and accessible only inside class A

           var parentUsername = super.username 
           // all ok in here, public property

           var parentServerURL = super.serverURL;
           // all ok, because it is protected

           // also we can call super.login(); or super.callServerForLogin();

      }

      // IMPORTANT we are also allowed to override public and protected functions
      override public function login():void
      {
          super.login(); 
          // we call the parent function to prevent loosing functionality;  

          Alert.show("Login called from class B");
      }

      override protected function callServerForLogin():void
      {
           super.callServerForLogin();
           // keep also parent logic

           Alert.show("calling protected method from B");
      }
 }


 // ----  Now considering you declare an object of type B you can do the following
 var bObj:B = new B();

 // access public properties and call public functions from both B and A
 bObj.username = "superhero";
 bObj.login();

 // will get compile error for next lines
 bObj.serverURL = "host.port";
 bObj.callServerForLogin();

AS3从子类访问超类变量

4 个答案: