依賴注入模式，是控制反轉（Inversion of Control，縮寫為IoC）的一種實作方式，主要是將依賴物件丟給接收物件中，就像是你想要用大頭菜發財致富，但大頭菜有那麼多顆，你不可能每顆都記住鈴錢單價、數量，所以你寫了一張便條紙，紀錄著大頭菜的類別、鈴錢單價、數量，然後貼在大頭菜上。
首先為了讓我們的大頭菜有個便條紙，所以我們要先建立大頭菜的組態文件 TrunipsConfiguration 並且將型別、鈴錢單價及數量帶入進去，為了防止外部物件直接碰到設定，所以需要獨立出 get 方法。
TurnipsConfiguration.php
use InvalidArgumentException;
/**
* Class TurnipsConfiguration.
*/
class TurnipsConfiguration
{
/**
* @var string
*/
protected $type;
/**
* @var int
*/
protected $price;
/**
* @var int
*/
protected $count;
/**
* TurnipsConfiguration constructor.
*
* @param string $type
* @param int $price
* @param int $count
*
* @throws InvalidArgumentException
*/
public function __construct(string $type, int $price, int $count)
{
$this->type = $type;
switch ($type) {
case '健康的大頭菜':
$this->price = $price;
$this->count = $count;
break;
case '壞掉的大頭菜':
$this->price = 0;
$this->count = $count;
break;
default:
throw new InvalidArgumentException('找不到這種大頭菜分類。');
}
}
/**
* @return int
*/
public function getType(): string
{
return $this->type;
}
/**
* @return int
*/
public function getPrice(): int
{
return $this->price;
}
/**
* @return int
*/
public function getCount(): int
{
return $this->count;
}
}再來將剛才建立的組態丟給大頭菜，並且透過 get 方法來去獲得組態設定，進而計算大頭菜的鈴錢總價。
Turnips.php
/**
* Class Turnips.
*/
class Turnips
{
/**
* @var TurnipsConfiguration
*/
protected $configuration;
/**
* Turnips constructor.
*
* @param TurnipsConfiguration $config
*/
public function __construct(TurnipsConfiguration $config)
{
$this->configuration = $config;
}
/**
* @return int
*/
public function calculatePrice(): int
{
return $this->configuration->getPrice() * $this->configuration->getCount();
}
}最後我們要寫一下測試，主要測試把組態丟進大頭菜後，能不能正確的計算價格，以及如果組態有錯誤，是否能獲得預期的錯誤。
- 測試正常的大頭菜是否可以賣鈴錢。
- 測試壞掉的大頭菜是否鈴錢價格為 0。
- 測試大頭菜組態檔如果給予不正確的類別，會獲得預期的錯誤。
DependencyInjectionTest.php
use InvalidArgumentException;
/**
* Class DependencyInjectionTest.
*/
class DependencyInjectionTest extends TestCase
{
/**
* 測試正常的大頭菜是否可以賣鈴錢。
*
* @test
*/
public function test_turnips_dependency_injection()
{
$config = new TurnipsConfiguration('健康的大頭菜', 100, 40);
$turnips = new Turnips($config);
$this->assertEquals(4000, $turnips->calculatePrice());
}
/**
* 測試壞掉的大頭菜是否鈴錢價格為 0。
*
* @test
*/
public function test_spoiled_dependency_injection()
{
$config = new TurnipsConfiguration('壞掉的大頭菜', 100, 40);
$turnips = new Turnips($config);
$this->assertEquals(0, $turnips->calculatePrice());
}
/**
* 測試大頭菜組態檔如果給予不正確的類別，會獲得預期的錯誤。
*
* @test
*/
public function test_undefined_dependency_injection()
{
$this->expectException(InvalidArgumentException::class);
$config = new TurnipsConfiguration('未知的大頭菜', 0, 0);
}
}最後測試的執行結果會獲得如下：
PHPUnit Pretty Result Printer 0.28.0 by Codedungeon and contributors.
==> Configuration: ~/php-design-pattern/vendor/codedungeon/phpunit-result-printer/src/phpunit-printer.yml
PHPUnit 9.2.6 by Sebastian Bergmann and contributors.
==> AbstractFactoryTest ✔ ✔ ✔ ✔
==> BuilderPatternTest ✔ ✔ ✔ ✔
==> FactoryMethodTest ✔ ✔ ✔ ✔
==> PoolPatternTest ✔ ✔
==> PrototypePatternTest ✔ ✔
==> SimpleFactoryTest ✔ ✔ ✔ ✔
==> SingletonPatternTest ✔
==> StaticFactoryTest ✔ ✔ ✔ ✔ ✔
==> AdapterPatternTest ✔ ✔
==> BridgePatternTest ✔ ✔ ✔
==> CompositePatternTest ✔ ✔ ✔
==> DataMapperTest ✔ ✔
==> DecoratorPatternTest ✔ ✔
==> DependencyInjectionTest ✔ ✔ ✔
Time: 00:00.050, Memory: 6.00 MB
OK (41 tests, 88 assertions)