PHP设计模式篇：选择适用于当前项目类型和规模的最佳模式

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在代码和项目中使用常见模式是有好处的，可以让代码更易于管理，同时也便于其他开发者理解你的项目。

如果你的项目使用了框架，那么在代码和项目结构上，都会遵循框架的约束，自然也就继承了框架中的各种模式， 这时你所需要考虑的是让上层代码也能够遵循最合适的模式。反之，如果没有使用框架，那么就需要你自己选择 适用于当前项目类型和规模的最佳模式了。

• Architectural pattern on Wikipedia
• Software design pattern on Wikipedia

Factory

One of the most commonly used design patterns is the factory pattern. In this pattern, a class simply creates the object you want to use. Consider the following example of the factory pattern:

<?php
class Automobile
{
    private $vehicle_make;
    private $vehicle_model;

    public function __construct($make, $model)
    {
        $this->vehicle_make = $make;
        $this->vehicle_model = $model;
    }

    public function get_make_and_model()
    {
        return $this->vehicle_make . ' ' . $this->vehicle_model;
    }
}

class AutomobileFactory
{
    public static function create($make, $model)
    {
        return new Automobile($make, $model);
    }
}

// have the factory create the Automobile object
$veyron = AutomobileFactory::create('Bugatti', 'Veyron');

print_r($veyron->get_make_and_model()); // outputs "Bugatti Veyron"

This code uses a factory to create the Automobile object. There are two possible benefits to building your code this way, the first is that if you need to change, rename, or replace the Automobile class later on you can do so and you will only have to modify the code in the factory, instead of every place in your project that uses the Automobile class. The second possible benefit is that if creating the object is a complicated job you can do all of the work in the factory, instead of repeating it every time you want to create a new instance.

Using the factory pattern isn’t always necessary (or wise). The example code used here is so simple that a factory would simply be adding unneeded complexity. However if you are making a fairly large or complex project you may save yourself a lot of trouble down the road by using factories.

• Factory pattern on Wikipedia

Singleton

When designing web applications, it often makes sense conceptually and architecturally to allow access to one and only one instance of a particular class. The singleton pattern enables us to do this.

<?php 
class Singleton
{
    static $instance;

    private function __construct()
    {
    }

    public static function getInstance()
    {
        if (!isset(self::$instance)) {
            self::$instance = new self();
        }

        return self::$instance;
    }
}

$instance1 = Singleton::getInstance();
$instance2 = Singleton::getInstance();

echo $instance1 === $instance2; // outputs 1

The code above implements the singleton pattern using a statically scoped variable and the getInstance() method. Note that the constructor is declared as private to prevent instantiation outside of the class via new keyword.

The singleton pattern is useful when we need to make sure we only have a single instance of a class for the entire request lifecycle in a web application. This typically occurs when we have global objects (such as a Configuration class) or a shared resource (such as an event queue).

You should be wary when using the singleton pattern, as by its very nature it introduces global state into your application, reducing testability. In most cases, dependency injection can (and should) be used in place of a singleton class. Using dependency injection means that we do not introduce unnecessary coupling into the design of our application, as the object using the shared or global resource requires no knowledge of a concretely defined class.

• Singleton pattern on Wikipedia

Front Controller

The front controller pattern is where you have a single entrance point for you web application (e.g. index.php) that handles all of the requests. This code is responsible for loading all of the dependencies, processing the request and sending the response to the browser. The front controller pattern can be beneficial because it encourages modular code and gives you a central place to hook in code that should be run for every request (such as input sanitization).

• Front Controller pattern on Wikipedia

Model-View-Controller

The model-view-controller (MVC) pattern and its relatives HMVC and MVVM let you break up code into logical objects that serve very specific purposes. Models serve as a data access layer where data it fetched and returned in formats usable throughout your application. Controllers handle the request, process the data returned from models and load views to send in the response. And views are display templates (markup, xml, etc) that are sent in the response to the web browser.

MVC is the most common architectural pattern used in the popular PHP frameworks.

Learn more about MVC and its relatives:

• MVC
• HMVC
• MVVM