Dagger2注入子对象

Question

Not sure the title is clear but what I actually have is :

module :

@Module
public class TestUserModule {

    User user;

    public TestUserModule(User user) {
        this.user = user;
    }

    @Provides
    @Singleton
    public User providesUser() {
        return user;
    }
}

Component :

@Singleton
@Component(modules = {TestUserModule.class})
public interface UserComponent {

    void inject(MyActivity activity);
    void inject(MyActivity2 activity);
}

in my App I create the component like this :

userComponent = DaggerUserComponent.builder().testUserModule(new TestUserModule(user)).build();

So, in my activity everything is ok, I can use @Inject User user; it works fine.

Now in my Activity, if I create an Object Foo, which look like this :

public class Foo {

@Inject
User user;

MyActivity activity;

public Foo(MyActivity activity){
this.activity = activity;
}
} 

By instantiating Foo in my activity with new Foo() , I know my user will not be injected.

So my question is, what I have to update in my code to be able to inject Foo object in my activity (I think this is the way to do if I want to inject User in Foo but tell me if I'm wrong) ?

Also, where is a good place to build my component ? Everything in the App ??

Thank's

Answer 1

You have 4 choices:

1. Use:

@Inject
Foo mFoo;

Use this approach if lifecycle of foo is exactly the same as lifecycle of your activity.

2. Use Lazy :

@Inject
Lazy<Foo> mLazyFoo;

and then when you need the instance of Foo :

Foo myFoo = mLazyFoo.get();

Use this approach if you will need just one Foo for the entire lifecycle of the activity.

3. Use Provider

@Inject
Provider<Foo> mFooProvider;

and when you need instance an instance of Foo

Foo myFooFirstInstance = mFooProvider.get();

Use this approach when you will need more than one instance of Foo in your activity.

4. Inject your foo manually (not recommended):

In your UserComponent declare void inject(Foo foo) and then in your method:

Foo myFoo = new Foo(...);
userComponent.inject(myFoo);

Also, where is a good place to build my component ? Everything in the App ??

For android app: yes, usually the component is built there.