如何在android中的MVP层之间使用注入？

Question

I have been using using dagger 2 in my project lately,

the problem is when I try to build my project, the presenter in my login activity which injected like below is null ,

and when I try to build the project

presenter cannot be provided without an @Inject constructor or from an @Provides- or @Produces-annotated method...

I don't understand what have I done wrong??, please someone help me with this,

thanks in advance.

Here is my Login Activity, the presenter here is null, which shows that, I've not injected it properly

@Inject
LoginPresenter presenter;
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    InjectHelper.getRootComponent().injectPresenter(this);
    presenter.setProgressBarVisiblity(View.INVISIBLE);
}

this is my presenter module

 @Module
 public class PresenterModule {
 private final LoginActivity activity;

public PresenterModule(LoginActivity activity) {
    this.activity = activity;
}

@Provides
@Singleton
public LoginActivity providesView() {

    return activity;
}
}


@Provides
@Singleton
public LoginPresenter providesPresenter()
{
    return new LoginPresenter();
}
}

this inject helper class

public class InjectHelper {
  private static RootComponent sRootComponent;

static {
    initModules();
}

private static void initModules() {
    sRootComponent = getRootComponentBuilder().build();
}

public static DaggerRootComponent.Builder getRootComponentBuilder() {
    return DaggerRootComponent.builder();
}

public static RootComponent getRootComponent() {
    if (sRootComponent == null) {
        initModules();
    }
    return sRootComponent;
}

}

this is root component class

@Singleton
@Component(modules = {
     PresenterModule.class
})
public interface RootComponent {
void injectLoginView(LoginPresenter loginPresenter);
}

Answer 1

you need to inform the dagger which views want to use injection, in your component. you must change the inject function code in your component to below:

    void inject(LoginActivity activity);

for showing dagger what you want, you need to use @dagger annotation NOT by sending it as inject function in component file. as you did properly:

@Inject
LoginPresenter presenter;

Dagger will search for a variable of type LoginPresenter in your module and finds the proper provider method using the type.

what you put in your component as a argument for "inject" function tells the Dagger what view you are going to do injection in (NOT what you want to inject)

Answer 2

@Singleton
@Component(modules = {PresenterModule.class})
public interface RootComponent {
    void inject(LoginActivity activity);
}