PHP / Laravel - 如果值不在url中，则父类应停止执行

I'm trying to create a very simple api, just to understand how to manage it.

I need to check if an "api key" is passed along side the url, my url should look like:

http://myapi.app/api/users?key=my-api-key
http://myapi.app/api/orders?key=my-api-key

So I have created a parent class to manage it in order to do not replicate all the login in every controller:

<?php

namespace App\Http\Controllers\Api;

use Illuminate\Http\Response as IlluminateResponse;
use Illuminate\Routing\Controller;
use Illuminate\Support\Facades\App;

class ApiController extends Controller {

    protected $isValid = true;

    public function __construct()
    {
        $request = App::make('Illuminate\Http\Request');

        if( ! $request->input('api_key') )
        {
            $this->isValid = false;
        }
    }

    /**
     * Per default lo status è 200 ovvero risposta corretta
     *
     * @var int
     */
    protected $statusCode = 200;

    /**
     * @return mixed
     */
    public function getStatusCode()
    {
        return $this->statusCode;
    }

    /**
     * @param mixed $statusCode
     * @return $this
     */
    public function setStatusCode( $statusCode )
    {
        $this->statusCode = $statusCode;

        return $this;
    }

    /**
     * @param string $message
     * @return mixed
     */
    public function respondNotFound( $message = 'Risorsa non trovata' )
    {
        return $this->setStatusCode( IlluminateResponse::HTTP_NOT_FOUND )->respondWithErrors( $message );
    }

    /**
     * @param string $message
     * @return mixed
     */
    public function respondInternalError( $message = "Errore interno del server" )
    {
        return $this->setStatusCode( IlluminateResponse::HTTP_INTERNAL_SERVER_ERROR )->respondWithErrors( $message );
    }

    /**
     * @param       $data
     * @param array $headers
     * @return mixed
     */
    public function respond( $data, $headers = [ ] )
    {
        return \Response::json( $data, $this->getStatusCode(), $headers );
    }

    /**
     * @param $message
     * @return mixed
     */
    public function respondWithErrors( $message )
    {
        return $this->respond( [
            'error' => [
                'message'     => $message,
                'status_code' => $this->getStatusCode()
            ]
        ] );
    }
} 

And this is my TestController

<?php

namespace App\Http\Controllers\Api;

class TestController extends ApiController {

    public function __construct()
    {
        parent::__construct();

        if( ! $this->isValid )
        {
            return $this->respondWithErrors("no no");
        }
    }

    public function test()
    {
        return "All ok";
    }
}

The problem is that if I visit the url with Postman or via browser and I do not set the key the test controller will always return All ok, what am I missing?

Looks like a visibility issue with your isValid variable http://php.net/manual/en/language.oop5.visibility.php

Change the variable to be public or a better option would be to add a public getter for the isValid variable in your parent class

public function isValid()
{
    return $this->isValid;
}

In any case middleware might be a better option for achieving this