依赖注入 简介

依赖注入 设计模式之一/方法
又名 控制反转 降低耦合度

课前准备知识

• interface
• implements
• Closure
  用于代表 匿名函数 的类
• instanceof
  用于确定一个 PHP 变量是否属于某一类 class 的实例
  来确定一个变量是不是继承自某一父类的子类的实例
• __Construct()
• call_user_func_array
  调用回调函数，并把一个数组参数作为回调函数的参数
• array_unshift
  在数组开头插入一个或多个单元

没有用依赖注入和控制反转的时候

<?php
class dog{
    function eat(){
        echo "dog to eat".PHP_EOL;
    }
}

class cat{
    function eat(){
        echo "cat to eat".PHP_EOL;
    }
}

class menu{
    function forEat(){
        $dog = new dog();
        $dog->eat();
        $cat = new cat();
        $cat->eat();
        // to kill
        echo "kill for eat".PHP_EOL;
    }
}

初步实现依赖注入

<?php

interface animal{
    function eat();
}

class dog implements animal{
    function eat(){
        echo "dog to eat".PHP_EOL;
    }
}

class cat implements animal{
    function eat(){
        echo "cat to eat".PHP_EOL;
    }
}


class menu{
    protected $obj = '';

    function __construct(animal $a){
        $this->obj = $a;
    }
    function forEat(){
        $this->obj->eat();
    }
}

$dog = new dog;
$m = new menu($dog);
$m->forEat();

终结版

<?php

interface animal{
    function eat();
}

class dog implements animal{
    function eat(){
        echo "dog to eat".PHP_EOL;
    }
}

class cat implements animal{
    function eat(){
        echo "cat to eat".PHP_EOL;
    }
}

class snake implements animal{
    protected $name = '';
    function __Construct($name){
        $this->name = $name;
    }

    function eat(){
        echo $this->name." snake to eat".PHP_EOL;
    }
}


class menu{
    protected $obj = '';

    function __construct(animal $a){
        $this->obj = $a;
    }
    function forEat(){
        $this->obj->eat();
    }
}

class Container{
    protected $binds;
    protected $instances;

    public  function bind($abstract,$concrete){
        if ($concrete instanceof Closure) { // 判断是不是闭包化
            $this->binds[$abstract] = $concrete;
        } else {
            $this->instances[$abstract] = $concrete;// 正常实例化
        }
    }

    public function make($abstract,$parameters=[]){
        if (isset($this->instances[$abstract])) {
            return $this->instances[$abstract];
        }
        array_unshift($parameters, $this);
        return call_user_func_array($this->binds[$abstract], $parameters);
    }
}

$obj = new Container;
$dog = new dog();
$obj->bind('Dog',$dog);
$want_eat = $obj->make('Dog');
$want_eat->eat();

$snake = new snake('neinei');
$obj->bind('Snake',$snake);
$snake_eat = $obj->make('Snake');
$snake_eat->eat();

$obj->bind('Cat',function(){
    return new cat;
});
$cat_eat = $obj->make('Cat');
$cat_eat->eat();