$ Object中的变量和变量范围

I am trying to write a class and I run into two errors.

class Foo {

    protected $count;

    function __construct() {
        $this->count = sizeof($_POST['some_key']);
    }

    static function get_count() {
        echo $this->count; // Problem Line
    }
}

$bar = new Foo;
$bar->get_count(); // Problem Call

The problem call is on the last line. using $this in the line with the "// Problem Line" comment generates a "Using $this when not in object context" error. Using "self::count" in place of "this->count" generates an "Undefined class constant error." What could I be doing wrong?

get_count is static. Static methods belong to the class, not the instance. As such, in a static method call, there is no this. Similarly, you can't reference concrete member variables (such as count) from within a static method.

In your example, I don't really understand why the static keyword is used (since all you're doing is echoing a member variable). Remove it.

I recommend you to do the following:

class Foo {

    protected $count;

    function __construct($some_post) {
        $this->count = sizeof($some_post);
    }

    function get_count() {
        echo $this->count;
    }
}

$some_post = $_POST['some_key'];
$bar = new Foo;
$bar->get_count($some_post);

OR:

class Foo {

    protected $count;

    function __construct() {
        global $_POST;
        $this->count = sizeof($_POST['some_key']);
    }

    function get_count() {
        echo $this->count;
    }
}

$bar = new Foo;
$bar->get_count();