Laravel 服务容器与服务提供者理解

参考
https://laravelacademy.org/po...
https://laravelacademy.org/po...

服务容器

控制反转(IOC)与依赖注入(DI)

讲的都是1个概念.

Ioc: 主对象依赖的某些对象原来在对象内部产生.现在把这个动作放到外面,比如Ioc容器,,IoC容器控制了对象生命周期,需要对象时，直接找容器，容器实例负责查找及创建依赖对象(也可以直接绑定已有对象的实例).

DI 由容器动态的将某个依赖关系注入到组件之中。依赖注入的目的并非为软件系统带来更多功能，而是为了提升组件重用的频率，并为系统搭建一个灵活、可扩展的平台, 这个平台就是基于IOC容器.

注入的原理是反射,根据类名创建实例,或者是Clouse,即闭包函数创建实例.

所以容器需要知道它负责的对象如何创建,这就是bind(绑定创建实例的闭包函数)和instance(绑定已有实例)的作用.

如何保存绑定大量对象?,就用array数组搞定:

#bind绑定后的binding数组:
[
    'A\1': 返回new的闭包函数 or 具体实现类 or 类名
    'A\2': 返回new的闭包函数 or 具体实现类 or 类名
]
#如果是`singleton`方法，实例存在instances数组,供下次使用.
[
    'A\1': A\1实例,
    'A\2': A\2实例
]

有了绑定关系，剩下的就是如何解析实例了,函数build,make,resolve等.

//container.php
$concrete = $this->getConcrete($abstract);
// We're ready to instantiate an instance of the concrete type registered for
// the binding. This will instantiate the types, as well as resolve any of
// its "nested" dependencies recursively until all have gotten resolved.
if ($this->isBuildable($concrete, $abstract)) {
    //build
    $object = $this->build($concrete);
} else {
    $object = $this->make($concrete);
}

最终的核心动作在build里, 如果concrete是closure,则调用产生，否则根据类名反射产生该实例

反射里应该是一颗递归树,因为class A的constructor参数里, 可能依赖B,B依赖C,D...

    public function build($concrete)
    {
        //...
        if ($concrete instanceof Closure) {
            return $concrete($this, $this->getLastParameterOverride());
        }
        try {
                $reflector = new ReflectionClass($concrete);
            } catch (ReflectionException $e) {
                throw new BindingResolutionException("Target class [$concrete] does not exist.", 0, $e);
        }
        //...
    }

bind的基本原理就这样了,而singleton是单例模式,生成的单例存储会先存储到instance数组.

服务提供者

所有类都这样手动bind,当然麻烦,于是就有service provider.

先register Provider, 它会调用每个Provider实例里的register和boot，完成具体的实例bind.

public function register($provider, $force = false)
    {
        if (($registered = $this->getProvider($provider)) && ! $force) {
            return $registered;
        }

        // If the given "provider" is a string, we will resolve it, passing in the
        // application instance automatically for the developer. This is simply
        // a more convenient way of specifying your service provider classes.
        if (is_string($provider)) {
            $provider = $this->resolveProvider($provider);
        }

        $provider->register();

        // If there are bindings / singletons set as properties on the provider we
        // will spin through them and register them with the application, which
        // serves as a convenience layer while registering a lot of bindings.
        if (property_exists($provider, 'bindings')) {
            foreach ($provider->bindings as $key => $value) {
                $this->bind($key, $value);
            }
        }

        if (property_exists($provider, 'singletons')) {
            foreach ($provider->singletons as $key => $value) {
                $this->singleton($key, $value);
            }
        }

        $this->markAsRegistered($provider);

        // If the application has already booted, we will call this boot method on
        // the provider class so it has an opportunity to do its boot logic and
        // will be ready for any usage by this developer's application logic.
        if ($this->isBooted()) {
            $this->bootProvider($provider);
        }

        return $provider;
    }