Usually the dependencies of a class are passed to the constructor and are available inside of the class during the whole lifecycle. With Method Injection it is possible to provide a dependency that is only needed by a single method of the class and passing it to the constructor may not be possible or may cause too much overhead in the majority of use cases.
A class method can be defined like the doSomething() method in the following example:
class MyClass extends \yii\base\Component
{
public function __construct(/*Some lightweight dependencies here*/, $config = [])
{
// ...
}
public function doSomething($param1, \my\heavy\Dependency $something)
{
// do something with $something
}
}
You may call that method either by passing an instance of \my\heavy\Dependency yourself or using yii\di\Container::invoke() like the following:
$obj = new MyClass(/*...*/);
Yii::$container->invoke([$obj, 'doSomething'], ['param1' => 42]); // $something will be provided by the DI container
