How can I make a Dagger2 injection nullable?

Question

Here I inject a SimpleDynamicString object to my presenter in a MVP structure. To avoid a NullPointerException, I have to implement this.

@Provides
@StringForTextView
static DynamicString provideDynamicString(Application application)
{
    return new SimpleDynamicString(application.getString(R.string.example_string));
}

Since I would like to use this one as a library, I am forced to implement everywhere.

Can I avoid this, so if (accidenataly or not) forgotten, no NullPointerException will happen?

What is `SimpleDynamicString`? What do you expect to happen, when if it's accidentally is forgotten? — azizbekian, Feb 02 '18 at 18:33
1. See link in beginning. 2. Nothing shall happen. Now I get an exception, when not providing the @Provides annotation. — Ralf Wickum, Feb 05 '18 at 11:27
@JoaquimLey https://stackoverflow.com/questions/48521957/dagger-androidinjector-cannot-be-provided-without-an-provides-annotated-method — Ralf Wickum, Feb 07 '18 at 11:01
@JoaquimLey data class SimpleDynamicString(val dynString: String) : DynamicString { override fun getDynamicString(): String { return dynString } } — Ralf Wickum, Feb 07 '18 at 11:01

score 2 · Answer 1 · answered Feb 08 '18 at 05:56

Your DynamicString's provides method is unscoped. StringForTextView is a qualifier annotation (meaning that Dagger can understand which DynamicString you want if you have more than one provides method). Also currently, because of your provides method is unscoped, Dagger is creating new instances when you inject.

If you want to use same instance of the DynamicString anywhere in your application, you need to create a Singleton component, put this provides method into a Singleton module and make the method's scope Singleton. If you make it Singleton, you can write one provides method and inject anywhere.

@Singleton
@Component(modules = {SingletonModule.class})
public interface SingletonComponent {

    @Component.Builder
    interface Builder {
        @BindsInstance
        Builder application(Application application);

        Builder singletonModule(SingletonModule singletonModule);

        SingletonComponent build();
    }

    void inject(YourClassToInject yourClassToInject);

}

@Module
public class SingletonModule {

    @StringForTextView // this is qualifier annotation
    @Singleton // this is scope annotation
    @Provides
    DynamicString provideDynamicString(Application application)
        return new SimpleDynamicString(application.getString(R.string.example_string));
    }
}

More information about scopes:

score 0 · Answer 2 · answered Feb 09 '18 at 09:17

0

I think you're asking about an optional binding.

@BindsOptionalOf abstract CoffeeCozy optionalCozy();

answered Feb 09 '18 at 09:17

Alexander Dadukin

504
3
12

How can I make a Dagger2 injection nullable?

2 Answers2