How to replace Slim::getInstance() in Slim 3 - php

Question

I am currently trying to follow a Slim tutorial that is utilizing $app = Slim::getInstance(); I don't know much about Slim, so the solutions to use a container do not make sense to me. What can I do to make my function provided below actually run?
function jsonResponse($data, $code = 200)
{
$app = Slim::getInstance();
$app->response->setStatus($code);
$app->response->headers->set(
'Content-type',
'application/json; charset=utf-8'
);
return $app->response->setBody(json_encode($data));
}
I am calling this inside another function for logging in that looks like this:
function login($request) {
$user = json_decode($request->getBody());
$username = $user->username;
$password = $user->password;
if (empty($username) || empty($password)) {
$error = 'Username and password are required';
// Bad request
return jsonResponse($error, 400);
}
$sql = "SELECT first_name, username FROM users "
. "WHERE username = '$username' AND password = '$password'";
$db = getConnection();
$row = array();
try {
$result = $db->query($sql);
if (!$result) {
$error = 'Invalid query: ' . mysql_error();
// Internal server error
return jsonResponse($error, 500);
}
$user = $result->fetchAll(PDO::FETCH_OBJ);
if (empty($user)) {
// Unauthorized
return jsonResponse($error, 401);
}
$row["user"] = $user;
$db = null;
} catch(PDOException $e) {
error_log('{"error":{"text":'. $e->getMessage() .'}}');
// $error = array( 'error' => array ( 'text' => $e->getMessage() ) );
// Internal server error
return jsonResponse($error, 500);
}
// OK, default is 200
return jsonResponse($row);
}
My route for the login function is $app->post('/login_user', 'login');
tl;dr I would like an explanation on how to convert older Slim code that uses getInstance().
Thank you!

Answer 1

It's actually pretty straightforward. In this particular case you don't need jsonResponse() function at all. Your login controller will need these changes:
function login($request, $response, $args) {
// ... some code ...
if ($isError) {
return $response->withStatus(500)->withJson($error);
}
return $response->withJson($row); // Status=200 is default.
}
In general, as was said in the comments, Slim3 has no static method to get a Singleton instance. If you wanted to hook on the response object in Slim3, the best way would be to create a middleware.
Or, if you really wanted to access $response from external function, you pass it as a function parameter (respecting dependency injection pattern and keeping code testable): jsonResponse($response, $error, 500);.
Technically, $app is a global variable, but I would suggest against accessing it through $GLOBALS.