20 Dagger Android Interview Questions and Answers

Dagger is a dependency injection library for Android that is used to create dagger components and modules. It is a popular tool among Android developers because it makes it easy to manage dependencies and to create custom views. If you are interviewing for an Android development position, it is likely that you will be asked questions about Dagger. In this article, we discuss the most common Dagger questions and how you should answer them.

Dagger Android Interview Questions and Answers

Here are 20 commonly asked Dagger Android interview questions and answers to prepare you for your interview:

1. What is Dagger?

Dagger is a dependency injection library for Android. It is used for injecting objects into other objects, such as activities and fragments. This allows for a more modular codebase, and can help to make code more testable and easier to maintain.

2. Can you explain what dependency injection is in the context of Android development?

Dependency injection is a technique used to remove the hard-coded dependencies from your code. This is especially useful in the context of Android development, where different components need to be able to communicate with each other. By using dependency injection, you can make sure that each component only has the dependencies that it needs, and that those dependencies can be injected at runtime.

3. How does using dependency injection benefit an app’s architecture?

There are a number of benefits to using dependency injection in an app’s architecture. First, it can help to decouple different parts of the app, making the code more modular and easier to maintain. Second, it can make it easier to test the app, since dependencies can be mocked or stubbed out. Finally, it can improve performance, since dependencies can be injected at compile time rather than being looked up at runtime.

4. What are some common issues with manual dependency injection?

There are a few common issues that can arise from manual dependency injection. First, it can be difficult to keep track of all of the dependencies that need to be injected. This can lead to forgetting to inject a dependency, or injecting a dependency that is no longer needed. Additionally, manual dependency injection can be error-prone, and lead to issues such as injecting a dependency in the wrong order.

5. How does Dagger help solve these problems?

Dagger is a powerful dependency injection tool that can help to solve many of the problems associated with traditional Android development, such as the need for boilerplate code and the potential for errors when dealing with complex dependencies. Dagger can help to make your code more concise and easier to maintain, and can also help to improve the performance of your app by reducing the number of times that dependencies need to be initialized.

6. What are the advantages of using Dagger for dependency injection?

There are several advantages to using Dagger for dependency injection, including the fact that it is a compile-time tool, which means that it can catch errors early on; it is also very efficient, since it generates code that is optimized for performance; and it is very easy to use, with a simple and straightforward syntax.

7. What are the disadvantages of using Dagger for dependency injection?

While Dagger is a powerful tool for dependency injection, it does have some disadvantages. First, it can be difficult to set up and configure, especially for larger projects. Second, it can lead to code that is difficult to read and understand, as it can be hard to follow the flow of dependencies. Finally, it can be slow, as the process of resolving dependencies can take some time.

8. Why do we use annotations when injecting dependencies?

Annotations help to make our code more readable and easier to understand. They also help to prevent errors by making sure that the correct dependencies are injected.

9. What are the different types of modules that can be created in Dagger 2?

There are four different types of modules that can be created in Dagger 2: @Module, @ContributesAndroidInjector, @Binds, and @Multibinds. @Module is used to define a class that contains methods to provide dependencies. @ContributesAndroidInjector is used to generate an AndroidInjector for a specific Activity or Fragment. @Binds is used to bind a concrete implementation to an interface or abstract class. @Multibinds is used to bind a map of keys to values.

10. What are the differences between the @Provides and @Binds annotations used to create a module?

@Provides is used when you need to create a new instance of a class, while @Binds is used when you need to bind an existing instance of a class to a provider.

11. What are the steps involved in creating a custom scoped component in Dagger 2?

The first step is to create a custom annotation that defines the scope. Next, create a module and annotate it with the custom scope annotation. In the module, bind the component to the custom scope. Finally, create the component and annotate it with the custom scope annotation.

12. What are the most commonly used annotations in Dagger 2?

The most commonly used annotations in Dagger 2 are @Inject and @Module. @Inject is used on fields, methods, and constructors to indicate that they should be injected by Dagger. @Module is used on classes to indicate that they are a Dagger module.

13. Can you give me an example of how to bind a service or activity to a provider method?

In your application class, you would create a field for your service or activity, annotated with @Inject. Then, in your Dagger module, you would bind your service or activity to the provider method. For example, if you were binding a service, you would do something like this:

@Module
public class MyModule {
@Provides
@Singleton
MyService provideMyService() {
return new MyService();
}
}

public class MyApplication extends Application {
@Inject
MyService myService;

@Override
public void onCreate() {
super.onCreate();
DaggerMyComponent.builder()
.myModule(new MyModule())
.build()
.inject(this);
}
}

14. Can you give me an example of how to inject data into a constructor using Dagger?

In order to inject data into a constructor using Dagger, you will need to create a module that provides the data. This module will need to have a @Provides annotation on the method that returns the data. Then, in your class that is injecting the data, you will need to create a @Inject annotation on the constructor.

15. What is lazy initialization and when should it be used?

Lazy initialization is when you delay the creation of an object until the point when it is needed. This can be useful in situations where creating the object is expensive or unnecessary until it is actually needed. For example, you might want to lazy initialize a database connection that is only used occasionally.

16. Is it possible to perform field injection on static fields? If yes, then why shouldn’t you?

Yes, it is possible to perform field injection on static fields using Dagger Android. However, it is generally not considered best practice to do so, as it can lead to unexpected behavior and can make your code more difficult to reason about and maintain.

17. What are the similarities and differences between Dagger 1 and Dagger 2?

Both Dagger 1 and Dagger 2 are dependency injection frameworks for Android. The main difference between the two is that Dagger 2 uses a compiler, while Dagger 1 does not. This means that Dagger 2 can provide more accurate error checking and can be more easily optimized. However, it also means that Dagger 2 is more difficult to set up and use.

18. What are some examples of where dependency injection must be used in Android apps?

Some examples of where dependency injection must be used in Android apps include when using third-party libraries, when using fragments, and when using Activities.

19. Are there any other tools available for Java/Android dependency injection?

There are a few other dependency injection tools available for Java and Android development, but Dagger is definitely one of the most popular. Some of the other options include Spring, Google Guice, and HK2.

20. What important things should I keep in mind when using Dagger in production?

There are a few things to keep in mind when using Dagger in production:

1. Make sure that you are using the latest version of Dagger, as new versions often include bug fixes and performance improvements.

2. When using Dagger for dependency injection, always use the @Inject annotation on your constructors to avoid accidentally injecting null values.

3. If you are using Dagger in a multi-threaded environment, be sure to use the @Singleton annotation on your injected objects to avoid race conditions.