Android和Java的依賴注入器：Dagger

Dagger是一個快速的Android和Java依賴注入器。

Use @Inject to annotate the constructor that Dagger should use to create instances of a class. When a new instance is requested, Dagger will obtain the required parameters values and invoke this constructor.

class Thermosiphon implements Pump {
  private final Heater heater;

  @Inject
  Thermosiphon(Heater heater) {
    this.heater = heater;
  }

  ...
}

Dagger can inject fields directly. In this example it obtains a Heater instance for the heater field and a Pump instance for the pump field.

class CoffeeMaker {
  @Inject Heater heater;
  @Inject Pump pump;

  ...
}

If your class has @Inject-annotated fields but no @Inject-annotated constructor, Dagger will use a no-argument constructor if it exists. Classes that lack @Inject annotations cannot be constructed by Dagger.

Dagger does not support method injection.

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