Why do actions with class and public method don't fire __construct() - wordpress

Question

I'm trying to understand how WordPress works with actions, classes, and methods.
If there is a class "TestClass" and it has a public method 'method1'
The method can be hooked to any action as "add_action('theHook', ['TestClass', 'method1']);"
From my understanding. If you don't initialize the class, you can not access its public methods and objects. Now, I would assume that WordPress has to follow this, and it must initialize my "TestClass", which will cause for public __construct() to fire.
However, after testing this, it does not fire __construct()..
Why is this?. I know a fix would be to self initialize inside 'method1', but I'm trying to figure out why WordPress behaves this way.

Answer 1

Because WordPress call your method as a static function: TestClass::method()
There is various solution:
1. Init class before add Action
Initialize your class before add action, like that:
$test = new TestClass();
add_action('hook', [$test, 'method']);
2. Call hook inside your Class:
class TestClass {
public function __construct() {
// Your construct
}
public function method() {
// Your Method
}
public function call_hook() {
add_action('hook', [$this, 'method']);
}
}
$test = new TestClass();
$test->call_hook();
3. Use a singleton
And if you need to to have only one instance of your class and call it in various place, you have to take a look to Singleton design pattern.
Demonstration:
class MySingletonClass {
private static $__instance = null;
private $count = 0;
private function __construct() {
// construct
}
public static function getInstance() {
if (is_null(self::$__instance)) {
self::$__instance = new MySingletonClass();
}
return self::$__instance;
}
public function method() {
$this->count += 1;
error_log("count:".$this->count);
}
}
$singleton = MySingletonClass::getInstance();
add_action('wp_head', [$singleton, 'method']);
$singleton2 = MySingletonClass::getInstance();
add_action('wp_footer', [$singleton2, 'method']);