如何从主范围内的子类中获取受保护的统计值 [英] How to get the protected stastic value from subclss in the main scope

问题描述

如何从子类获取值作为主作用域中受保护的 ststic 属性.我在这些行中使用，但不起作用.

How can i get the value frome child class as a protected ststic attribute in the main scope. I use in these lines but it doesn't work.

self::$table_name="Table_shape_B";
self::$table_name="Table_shape_C";

我想看看这些台词谢谢.

I want to see these lines Thanks.

selected Database Table name: Table_shape_B
selected Database Table name: Table_shape_C

输出是

new B : are created :
new C : are created :
selected Database Table name:
selected Database Table name:

这是我的代码:

<?php
    abstract class Class_A {

      protected static $table_name;
         //Class_B Database Table name =  "Table_shape_B"
         //Class_CA Database Table name =  "Table_shape_C"
        public function __construct()   {
            echo "<br />"." new ".get_class($this)." : are created :";
        }

        public function get_table_name_protected() {
            return self::$table_name;
        }
    }

    class B extends Class_A {
        //self::$table_name="Table_shape_B";
    }

    class C extends Class_A     {
     //self::$table_name="Table_shape_C";
    }

    $NewObject1= new B ( );
    $NewObject2= new C ( );

    echo "<br />".' selected Database Table name: '.$NewObject1->get_table_name_protected();
    echo "<br />".' selected Database Table name: '.$NewObject2->get_table_name_protected();

 ?>

推荐答案

参见 http://docs.php.net/language.oop5.late-static-bindings

从 PHP 5.3.0 开始，PHP 实现了一个称为后期静态绑定的功能，可用于在静态继承的上下文中引用被调用的类.[...] 后期绑定"来自这样一个事实，即 static:: 不会使用定义方法的类来解析，而是使用运行时信息来计算.它也被称为静态绑定"，因为它可以用于(但不限于)静态方法调用.

As of PHP 5.3.0, PHP implements a feature called late static bindings which can be used to reference the called class in a context of static inheritance. [...] "Late binding" comes from the fact that static:: will not be resolved using the class where the method is defined but it will rather be computed using runtime information. It was also called a "static binding" as it can be used for (but is not limited to) static method calls.

不幸的是，您不能像使用抽象成员方法那样强制"子类定义这个静态成员.

Unfortunately you can't "force" a subclass to define this static member like you can with abstract member methods.

<?php
abstract class Class_A {

    public function __construct()   {
        echo get_class($this), "\n";
    }

    public function get_table_name_protected() {
        return static::$table_name;
    }
}

class B extends Class_A {
    protected static $table_name="Table_shape_B";
}

class C extends Class_A     {
    protected static $table_name="Table_shape_C";
}

$NewObject1= new B ( );
$NewObject2= new C ( );

echo $NewObject1->get_table_name_protected(), "\n";
echo $NewObject2->get_table_name_protected(), "\n";

印刷品

B
C
Table_shape_B
Table_shape_C

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