0

如何从子类中获取值作为主范围内的受保护 ststic 属性。我在这些行中使用，但它不起作用。

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

我想看看这些线谢谢。

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();

 ?>
4

3 回答 3

2

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

自 PHP 5.3.0 起，PHP 实现了一种称为后期静态绑定的功能，该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:: 不会使用定义该方法的类来解析，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。

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。

<?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

B
C
Table_shape_B
Table_shape_C
于 2012-05-08T06:37:02.613 回答
1

[编辑] 早餐后，我意识到这段代码在我正在研究的 CMS 中会有多酷。并利用数组完成了它。

<?php

error_reporting(E_ALL);

abstract class Class_A {

    protected static $table_name = array();

    public function __construct()   {
        $tmp = get_class($this);
        echo "<br />"." new ".$tmp." : are created :";
        self::$table_name[$tmp] = "Table_shape_" . $tmp;
    }

    public function get_table_name_protected() {
        $tmp = get_class($this);
        return self::$table_name[$tmp];
    }
}

class B extends Class_A {

}

class C extends Class_A {

}

$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();

?>

旧的输出，一次完成 1 个：

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

新输出：

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

我真的要感谢发帖人提出这样一个有趣的问题。希望这可以帮助。

于 2012-05-08T06:57:04.833 回答
0

但是为什么你需要静态变量呢？

abstract class Class_A
{

    /**
    * Hold table name
    * @var string
    */
    protected $table_name = null;

    /**
    * Get protected table name
    * @return string
    * @throws RuntimeException
    */
    public function get_table_name_protected()
    {
        if (null === $this->table_name) {
            throw new RuntimeException('Table name is not defined');
        }
        return $this->table_name;
    }
}

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

class Class_C extends Class_B
{
    protected $table_name = "Table_shape_C";
}
于 2012-05-08T07:24:49.063 回答