帮助我理解$this是如何在PHP中使用的

一旦进入一个对象的函数,您就可以完全访问它的变量,但是要设置它们,您需要比仅仅使用您想要使用的变量名更具体。要正确指定要使用局部变量,需要使用 $this 变量,PHP总是将其设置为指向当前使用的对象。

例如:

function bark()
{
    print "{$this->Name} says Woof!\n";
} 

无论何时在对象的函数中,PHP都会自动设置 $这个 变量包含该对象。您不需要做任何事情就可以访问它。

从对象上下文中调用方法时可用的伪变量。它是对调用对象的引用(通常是该方法所属的对象,但如果该方法是从辅助对象的上下文静态调用的,则可能是另一个对象)

<?php
class A
{
    function foo()
    {
        if (isset($this)) {
            echo '$this is defined (';
            echo get_class($this);
            echo ")\n";
        } else {
            echo "\$this is not defined.\n";
        }
    }
}

class B
{
    function bar()
    {
        // Note: the next line will issue a warning if E_STRICT is enabled.
        A::foo();
    }
}

$a = new A();
$a->foo();

// Note: the next line will issue a warning if E_STRICT is enabled.
A::foo();
$b = new B();
$b->bar();

// Note: the next line will issue a warning if E_STRICT is enabled.
B::bar();
?>

$this is defined (A)
$this is not defined.
$this is defined (B)
$this is not defined.

详细说明shamittomar:

$这是一个句柄,可以引用在其中完成调用的当前对象。(所以它基本上指向自己。假设我们有同一个类的多个对象,我们想在做最终的移动之前用(不同的)数据来设置它:echo it。 当您不知道对象名称时,很难指向它自己。

class SaySomething{
        private $the_line;// the variable exists only in this class!
        public function __construct($myline){
            $this->the_line = $myline;
           // see how it points to itself?
           // would there be a variable in the global scope then it would be not possible to "setup"
           // the object without it getting overwritten in the next setup.
        }

        //The function to echo the stuf. Can be callid by the "outside world"
        public function say_it(){
            echo $this->the_line;
            $this->add_exclamation();//call the function add_exclamation in this class/object.
        }

       //This function can not be called by the outside world because it's private.
       // The only way to call it is from inside this class. To point to this class and call the function:
       // $this->add_exclamation();
        private function add_exclamation(){
            echo "!";
        }

    }

    $obja = new SaySomething('my');
    $objb = new SaySomething('sample');
    $objc = new SaySomething('super');
    $objd = new SaySomething('text');

    //Mind: uptill nothing has been said, only the private variable $the_line has been set in the constructor.
    $obja->say_it();
    $objc->say_it();
    $objb->say_it();
    $objd->say_it();

http://www.slideshare.net/sebastian_bergmann/understanding-the-php-object-model