如何在PHP中设置父变量并从子进程访问它？

I'm trying to switch to OOP way of programming in PHP. I'm running into the issues with multiple children and one single parent classes.

In my parent's construct method I include a child class file with include() method and then create a variable referencing the child class like so:

class App {
    function __construct() {
        include_once('childClass.php');
        $this->childvar = new childClass;

        include_once('childClass2.php');
        $this->childvar2 = new childClass2;
    }
}

And my child classes are as follows:

class childClass extends App {
    var test = 1;

    function __construct() {

    }
}

class childClass2 extends App {
    function __construct() {
        echo $this->childvar->test;
    }
}

When I try to access a childClass vriable from childClass2 I get an error

Undefined property: childClass2::$test

What am I doing wrong here?

If you want to use the constructor of App in childClass2 make sure you call parent::__construct(); first.

class childClass2 extends App {
    function __construct() {
        parent::__construct();
        echo $this->childvar->test;
    }
}

Keep in mind that as it is this will create an infinite loop.

In general it is not common to see a new call in a constructor. Any dependencies should be passed in. This incidentally also deals with the infinite loop. Your current design has more problems though.

class App {
    function __construct($child1, $child2) {
        $this->child1 = $child1;
        $this->child2 = $child2;
    }
}
class childClass extends App {
    var test = 1;

    function __construct($child1, $child2) {
        parent::__construct($child1, $child2);
    }
}

class childClass2 extends App {
    function __construct($child1, $child2) {
        parent::__construct($child1, $child2);
        echo $this->childvar->test; // error childvar is null
    }
}

$app = new App(new childClass(null, null), new childClass2(null, null));