PHP类：通过构造函数分配静态属性

Question

Simplified example of a class:

class Table extends TableAbstract{
    protected static $tablename;

    function __construct($str){
       $this->tablename = "table_" . $str;
       $this->insert();    // abstract function
    }

}

When I've used classes like this in the past I've assigned the $tablename directly when writing the class. This time however I would like it to be decided by the constructor. But when I then call the function referencing $tablename the variable seems to be empty, when I echo the SQL.

What am I doing wrong, or could someone suggest a way to achieve what I want here?

Thanks for any comments/answers..

Answer 1

由于属性是static ，使用Table::$tablename - 或者self::$tablename来访问它以隐式引用当前类。

Answer 2

when accessing a static property you need to use self::$varName instead of $this->varName . Same thing with static methods.

Edit: Just to highlight some differences between abstract and static/non-static properties, I made a small example.

<?php
abstract class A{
    public abstract function setValue($someValue);

    public function test(){
        echo '<pre>';
        var_dump($this->childProperty);
        var_dump(B::$childStatic);
        echo '</pre>';
    }
}

class B extends A{
    protected $childProperty = 'property';
    protected static $childStatic = 'static';

    public function setValue($someValue){
        $this->childProperty = $someValue;
        self::$childStatic = $someValue;
    }
}

//new instance of B
$X = new B();
//another new instance of B
$Y = new B();

//output the values
$X->test();
$Y->test();

//change the static and standard property in $X
$X->setValue("some new value");

//output the values again.
$X->test();
$Y->test();
?>

Output:

string(8) "property"
string(6) "static"

string(8) "property"
string(6) "static"

string(14) "some new value"
string(14) "some new value"

string(8) "property"
string(14) "some new value"

After you call setValue on $X, it you can see that the values of the static property change in both the instances while the non-static property changes only in that one instance.

Also, I just learned something. In a method of an abstract class trying to access a static child property, you have to specify the child class name to access the property, self:: doesn't work and throws an error.

Answer 3

If you would google up such thing as php static you would have found that:

From PHP Manual :

Static Keyword

Static properties cannot be accessed through the object using the arrow operator ->.

Answer 4

static properties are set on the class, not on an instance. Get rid of the static to make your $tablename a normal instance property and it should work as expected.

Answer 5

a static member is not tied up to the instance but it's more related to the class, so you can't really reference a static member through $this . you should use self::$staticMemberName to access a static member from within a class instance.