如何使匕首2中的子组件单例？ [英] How to make subcomponent singleton in dagger 2?

问题描述

我希望将我的子组件设置为单例，以便我也可以使Login Presenter也成为单例。

I want to make my subcomponent to be a singleton so that I can have Login Presenter to be a singleton as well. Is this possible?

@Singleton
@Component(modules = AppModule.class)
public interface AppComponent {
    LoginComponent getLoginComponent();
}

@Singleton
@Subcomponent(modules = LoginModule.class)
public interface LoginComponent {
}

public class LoginComponent {
    @Singleton
    LoginPresenter getLoginPresenter();
}

推荐答案

@Subcomponent 不能做成 @Singleton 。

@Singleton 规范对此有点含糊， singleton通常表示每个应用程序一个。由于 @Subcomponent 是通过工厂方法在组件上创建的，因此 only 方式中，与单例绑定的实例为每个应用程序一个 如果单例子组件是单例组件的子代，并且其工厂方法在每个应用程序中仅被调用一次。强制执行该约束实际上是不可能的，因此该模式仅可能是错误的来源。

While the @Singleton spec is a little vague about it, "singleton" canonically means "one per application". Since a @Subcomponent is created via a factory method on a component, the only way in which your singleton-bound instances would be "one per application" would be if the singleton subcomponent were a child of a singleton component and its factory method were only ever invoked once per application. Enforcing that constraint is virtually impossible, so the pattern would just be a likely source of bugs.

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