有人帮助我以更简单的方式理解魔法。
我知道魔术方法是在代码的某个点触发的,我不明白的是它们被触发的点。 就像__construct()一样,它们是在创建类的对象时触发的,要传递的参数是可选的。
请特别在__get()
,__set()
,__isset()
,__unset()
被触发时告诉我。如果说明任何其他魔术方法,将会非常有用。
答案 0 :(得分:2)
PHP的魔术方法都以“__”开头,只能在类中使用。我试着在下面写一个例子。
class Foo
{
private $privateVariable;
public $publicVariable;
public function __construct($private)
{
$this->privateVariable = $private;
$this->publicVariable = "I'm public!";
}
// triggered when someone tries to access a private variable from the class
public function __get($variable)
{
// You can do whatever you want here, you can calculate stuff etc.
// Right now we're only accessing a private variable
echo "Accessing the private variable " . $variable . " of the Foo class.";
return $this->$variable;
}
// triggered when someone tries to change the value of a private variable
public function __set($variable, $value)
{
// If you're working with a database, you have this function execute SQL queries if you like
echo "Setting the private variable $variable of the Foo class.";
$this->$variable = $value;
}
// executed when isset() is called
public function __isset($variable)
{
echo "Checking if $variable is set...";
return isset($this->$variable);
}
// executed when unset() is called
public function __unset($variable)
{
echo "Unsetting $variable...";
unset($this->$variable);
}
}
$obj = new Foo("hello world");
echo $obj->privateVariable; // hello world
echo $obj->publicVariable; // I'm public!
$obj->privateVariable = "bar";
$obj->publicVariable = "hi world";
echo $obj->privateVariable; // bar
echo $obj->publicVariable; // hi world!
if (isset($obj->privateVariable))
{
echo "Hi!";
}
unset($obj->privateVariable);
总之,使用这些魔术方法的一个主要优点是,如果您想要访问类的私有变量(这违反了许多编码实践),但它确实允许您为特定事物的时间分配操作执行;即设置变量,检查变量等
请注意,__get()
和__set()
方法仅适用于私有变量。
答案 1 :(得分:0)
以双下划线开头的PHP函数 - __
- 在PHP中称为魔术函数(和/或方法)。它们是始终在类中定义的函数,并不是独立的(在类之外)函数。 PHP中可用的神奇功能是:
__ construct(),__ desttruct(),__ call(),__ callStatic(),__ get(),__ set(),__ isset(),__ unit(),_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ,__ set_state(),__ clone()和__autoload()。
现在,这是一个具有__construct()
魔术功能的类的示例:
class Animal {
public $height; // height of animal
public $weight; // weight of animal
public function __construct($height, $weight)
{
$this->height = $height; //set the height instance variable
$this->weight = $weight; //set the weight instance variable
}
}