如何在PHP

Question

初始化变量构造

我写这个简单的代码，不知道用什么构造的问题是：

class Animal { 
    public $_type; 
    public $_breed; 

    public function __construct ($t, $b) { 
     echo "i have initialized<br/>"; 

     $this ->_type = $t; 
     $this ->_breed = $b; 
     echo "type is " .$_type. "<br/>"; 

     echo "breed is " .$_breed. "<br/>"; 
    } 

    public function __destruct() { 
     echo "i am dying"; 
    } 
} 

$dog = new Animal("Dog", "Pug"); 

Answer 1

试试这个（注意回声线）使用方法：

class Animal { 
    public $_type; 
    public $_breed; 

    public function __construct ($t, $b) { 
     echo "i have initialized<br/>"; 

     $this->_type = $t; 
     $this->_breed = $b; 

     //You have to use '$this' keyword to access 
     //class attibutes: 
     echo "type is " . $this->_type . "<br/>"; 
     echo "breed is " . $this->_breed . "<br/>"; 
    } 

    public function __destruct() { 
     echo "i am dying"; 
    } 
} 

Answer 2

为什么你有$this后的空间？删除空间。
另外，调用变量时添加$this。

class Animal { 
    public $_type; 
    public $_breed; 

    public function __construct ($t, $b) { 
     echo "i have initialized<br/>"; 

     $this->_type = $t; // <-- remove space 
     $this->_breed = $b; // <-- remove space 
     echo "type is " .$this->_type. "<br/>"; // <-- add $this 

     echo "breed is " .$this->_breed. "<br/>"; // <-- add $this 
    } 

    public function __destruct() { 
     echo "i am dying"; 
    } 
} 

Answer 3

$ _type和$ _breed是类的变量，所以你需要使用this关键字

echo "type is " .$this->_type. "<br/>"; 
    echo "breed is " .$this->_breed. "<br/>"; 

Answer 4

要初始化他们很好，但检索他们错了...

由于$_type和$_breed对象级别的作用域，你需要告诉PHP什么范围你在引用它们。

因此，与其

echo $_breed; 

你需要

echo $this->_breed; 

在一个侧面说明，现在在变量名前加上_这是非常奇怪的做法，如果它们是公共变量，则更是如此。这可能会混淆其他开发人员使用您的代码。

Answer 5

虽然这不违反PHP语法，我认为，这两条线

echo "type is " .$dog->_type. "<br/>"; 
echo "breed is " .$dog->_breed. "<br/>"; 

不能放在__construct()而不是使用这个类外，

这样，

class Animal { 
    public $_type; 
    public $_breed; 

    public function __construct ($t, $b) { 
    $this ->_type = $t; 
    $this ->_breed = $b; 
    } 
    public function __destruct() { 
     echo "i am dying"; 
    } 
} 

$dog = new Animal("Dog", "Pug"); 
echo "i have initialized<br/>"; 
echo "type is " .$dog->_type. "<br/>"; 
echo "breed is " .$dog->_breed. "<br/>";