Laravel binding绑定的用途和目的是什么

即使没有那种奇怪的"绑定"，它也可以工作，对吗？

Not really. Sure it can work just fine if the required dependencies are simple to instantiate. Let's say you have this simple class Foo stored in app directory:

<?php

namespace App;

class Foo
{
    public function hello()
    {
        return 'Hello World';
    }
}

You can type hinted this class without binding it first in the container. Laravel will still be able to resolve this class. Let's say you type-hinted it like this in the routes:

Route::get('/foo', function (App\Foo $foo) {
    return $foo->hello(); // Hello World
});

We can even go further, let's say this Foo class required another simple class Bar. Our Bar class looks like this:

<?php

namespace App;

class Bar
{
    public function hello()
    {
        return 'bar';
    }
}

我们的Foo个班级现在看起来是这样的:

<?php

namespace App;

class Foo
{
    public function __construct(Bar $bar)
    {
        $this->bar = $bar;
    }

    public function hello()
    {
        return $this->bar->hello();
    }
}

Will Laravel be able to resolve the type-hinted Foo class now? YES! Laravel will still be able to resolve this Foo class.

Now the issue will come in when our Foo class needs slightly more complex dependencies that need to be configured. Imagine that our Foo class simply need the name of our application. Sure you can simply use config('app.name') within the class's method, but imagine that this can be an HTTP client that requires a configuration array to instantiate.

<?php

namespace App;

class Foo
{
    public function __construct($appName)
    {
        $this->appName = $appName;
    }

    public function hello()
    {
        return "Hello {$this->appName}";
    }
}

拉威尔现在能解决这门课吗？不是的.Service Container人出手相救！您可以通过将这个Foo类绑定到服务容器中来教Laravel如何解析它.您可以在app\Providers\AppServiceProvider.php文件的register方法内定义绑定:

public function register()
{
    $this->app->bind(\App\Foo::class, function ($app) {
        // Pass the application name
        return new \App\Foo($app->config['app.name']);
    });
}

And sometimes, you don't want multiple instances to be created. Like our Foo class for instance, there's no need for multiple instances for this kind of class. In this case, we can bind it with singleton method.

$this->app->singleton(\App\Foo::class, function ($app) {
    return new \App\Foo($app->config['app.name']);
});

More Important Usage

But the more important usage of this service container is that we can bind an interface to it's implementation. Let's say we have this PaymentProcessorInterface with pay method:

<?php

namespace App;

interface PaymentProcessorInterface
{
    public function pay();
}

Then we have the implementation of this interface named StripeProcessor:

<?php

namespace App;

class StripeProcessor implements PaymentProcessorInterface
{
    public function pay()
    {
        return 'pay with stripe';
    }
}

使用服务容器，我们可以绑定PaymentProcessorInterface到StripeProcessor类:

$this->app->bind(\App\PaymentProcessorInterface::class, function () {
    return new \App\StripeProcessor();
});

We can then type-hinted PaymentProcessorInterface within our code:

Route::get('/pay', function (App\PaymentProcessorInterface $paymentProcessor) {
    return $paymentProcessor->pay(); // pay with stripe
});

通过这种方式，我们可以轻松地交换PaymentProcessorInterface实现.假设我们想要将支付处理器更改为Paypal，那么我们有这个PaypalProcessor类.

<?php

namespace App;

class PaypalProcessor implements PaymentProcessorInterface
{
    public function pay()
    {
        return 'pay with paypal';
    }
}

我们所要做的就是更新绑定:

$this->app->bind(\App\PaymentProcessorInterface::class, function () {
    return new \App\PaypalProcessor();
});

希望这能给你一些 idea .