AS3访问子类的超类变量

Question

我希望有人可以解释有关访问超类的变量的子类。

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？

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

有一对夫妇的事情，这里要注意，首先，访问一个超类的属性时，你不需要做：

super.test_declared_early 

而只是：

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。你还没有分配它的价值！必须调用init，否则您需要手动设置它。

编码愉快！

Answer 2

感谢关于不需要超级的提示。

不过，我并没有明确这一点，但该计划的另一部分调用init：

在GameScreen类：前

_character.init(this); 

把一丝

test_declared_late = "declared late"; 

显示它被称为。另外，如果init没有被调用，代码就不会到达骑士构造函数。

如果你有时间，我真的很感激，如果你能签出源 http://www.mediafire.com/?46zwpfo4h47cdaq

谢谢！

Answer 3

我几乎是积极的我在调用init之后追踪它。在这里，我增加了一些痕迹，表明这里我呼吁初始化代码：

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); 
     } 
    } 

} 

字符类别：

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，但它仍然看起来像我调用init并设置变量，然后再在子类中找到它。

感谢您的帮助！

Answer 4

我真的建议你检查什么私人，保护和公共手段。 我不会在这篇文章中写一本关于OOP的书，所以我想请你检查一下基本知识。

我会做什么我会给你一个关于如何使用和声明变量的示例。

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();