I lose my session with PHP - php

Question

I have a problem with a project I'm working on. I'm trying to code a simply login system using PHP + Sessions. But I lose my session, and I don't really know why, the code:
index.php
<?php
session_start();
if(!isset($_SESSION['logedin'] == True)){
<form action = "login.php" method = "post" id="login-form" class = "login-form">
<input type = "text" name = "username" maxlength = "100"/>
<input type = "password" maxlength = "50" name = "password"/>
<button type="submit">Sign in</button>
</form>
}else{
echo "Loged in.";
}
?>
login.php
<?php
session_start();
$username = $_POST['username'];
$password = $_POST['password'];
if(!isset($_SESSION['logedin'] == True)){
if($username == 'username' && $password == 'password'){
$_SESSION['logedin'] = True;
header("index.php"); // Loged in
}
}
?>
The real code is not this one, because it's too long to put here, but this is a simply resume about the code... I'm losing my head, because if I open a session into index.php, it works, but if I go out of my page (in this case, login.php through form), when I back to index, session just vanish...
I got to say I don't use any frameworks or something, it's a simply form, all done with PHP.

Answer 1

Your parens on the first line are going to be a problem:
if(!isset($_SESSION['logedin'] == True)){
Change to:
if(!isset($_SESSION['logedin'])) {
Why are you doing a double negative on this condition? Instead of doing !isset == true, just do isset == false. This is just likely to add confusion to your code, and the more intuitive (and simplistic) your code, the better.
In your login.php you also have that line:
if(!isset($_SESSION['logedin'] == True)){
You are basically saying isset(true) == false which should always return false. Because $_SESSION['logedin'] == true is true. Change it to if (isset($_SESSION['logedin'])) which will be true if you're logged in.
Let's break this condition down a little further to see what you're doing
if (false == isset(
$_SESSION['loged'] == true // will be true if you're logged in
) // isset will return true, but you're expecting a false
)
Your isset is always going to return true. Whether $_SESSION['logedin'] == true returns true or false it will be "isset". Isset will only return false if the return value is null or the var does not exist. "False" is a value and exists. Does that make sense? Sorry if this is confusing. Basically, don't use conditions in your isset! :). Use the isset as a part of a condition, but don't pass them into the isset parameter.