Error Using Middleware in SLIM Framework

I have been at this for hours now and can not seem to figure out why it's not working. This my first time using SLIM and my first exposure to middleware. I am trying to follow the tutorial listed on the slim website but just can't get to work.

My bootstrap code:

<?php

  require '../vendor/autoload.php';

  $app = new Slim\Slim();


  $app->get('/test', function() {

    echo 'Hello, World'; 
 }); 

$mw = function ($request, $response, $next) {
    $response->getBody()->write('BEFORE');
    $response = $next($request, $response);
    $response->getBody()->write('AFTER');

    return $response;
};


$app->add($mw); 
$app->run();

When I run just my slim url without the middleware it runs fine. I get Hello, World as the output when I runt http://mysite/test. But when I add the middleware code as listed on the slim site I get the following error:

Catchable fatal error: Argument 1 passed to Slim\Slim::add() must be an instance of Slim\Middleware, instance of Closure given, called in /Applications/XAMPP/xamppfiles/htdocs/project/api/public/index.php on line 22 and defined in /Applications/XAMPP/xamppfiles/htdocs/academy/api/vendor/slim/slim/Slim/Slim.php on line 1267

Am I missing something? Does the middleware require some other setup? The slim documentation is not very helpful when it comes to this. Any help appreciated.

Solution

You seem to have installed Slim 2. You are also mixing Slim 2 and Slim 3 syntax. To install Slim 3 issue the following command.

$ composer install slim/slim

Then use code like following:

<?php

require "vendor/autoload.php";

$app = new \Slim\App;

$mw = function ($request, $response, $next) {
    $response->getBody()->write("BEFORE");
    $response = $next($request, $response);
    $response->getBody()->write("AFTER");

    return $response;
};

$app->add($mw); 

$app->get("/test", function ($request, $response) {
    echo "Hello, World"; 
});

$app->run();