PHP（OOP）：如何在每个方法中调用一个新方法

Let's say I have a Class

<?php

class MyClass extends OtherClass
{
    public function foo()
    {
    // some stuff
    }
    public function bar()
    {
    // some stuff
    }
    public function baz()
    {
    // some stuff
    }
}

Now I need to add another method, that need to be called from every other method.

private function run_this()
{
$mandatary = true;
return $mandatary;
}

I can add a simple $this->run_this() in every method, OK, but is it possible to add some "magic" recipient to invoke run_this() from every method of this class?

Not entirely sure what you want, but if you want it availabe to all child objects I would put it in other class as a protected function. That way only child objects have access to it.

class OtherClass {
protected function run_this()
    {
    $mandatary = true;
    return $mandatary;
    }
}

class MyClass extends OtherClass
{
    public function foo()
    {
    $mandatory = $this->run_this();
    // some stuff
    }
    public function bar()
    {
    $mandatory = $this->run_this();
    // some stuff
    }
    public function baz()
    {
    $mandatory = $this->run_this();
    // some stuff
    }
}

Could you not use the constructor ?

<?php

class MyClass extends OtherClass
{
    function __construct() {
       $mandatory = $this->run_this();
    }
    private function run_this()
    {
        $mandatary = true;
        return $mandatary;
    }
    public function foo()
    {
    // some stuff
        if ($this->mandatory) {
            //true
        } else {
            //false 
        }
    }
    public function bar()
    {
    // some stuff
    }
    public function baz()
    {
    // some stuff
    }
}

well some variation of that.

I still reeeeally think you are doing something because you have a design issue somewhere (XY problem), however if you insist in doing what you asked you could decorated the class:

class OtherClass {}

class MyClass extends OtherClass
{
    public function foo()
    {
    // some stuff
    }
    public function bar()
    {
    // some stuff
    }
    public function baz()
    {
    // some stuff
    }

    public function run_this()
    {
        $mandatary = true;
        return $mandatary;
    }
}

class MyClassDecorator
{
    private $myClass;

    public function __construct($myClass)
    {
        $this->myClass = $myClass;
    }

    public function __call($name, array $arguments)
    {
        // run the mthod on every call
        $this->myClass->run_this();

        // run the actual method we called
        call_user_func_array ([$this->myClass, $name], $arguments)
    }
}

$myClass   = new MyClass();
$decorator = new MyClassDecorator($myClass);

// will first run the `run_this` method and afterwards foo
$decorator->foo();
// etc
//$decorator->bar();

It's a bit hard to tell and the above works like you asked, however as stated before this is most likely not what you actually want to do.