Architecture Patterns

This chapter will introduce you to architectural patterns you can use for your Android projects. It covers using the Model-View-ViewModel (MVVM) pattern, adding ViewModels, and using data binding. You will also learn about using the Repository pattern for caching data and WorkManager for scheduling data retrieval and storage.

By the end of the chapter, you will be able to structure your Android project using MVVM and data binding. You will also be able to use the Repository pattern with the Room library to cache data and WorkManager to fetch and save data at a scheduled interval.

In the previous chapter, you learned about using Coroutines and Flow for background operations and data manipulation. Now, you will learn about architectural patterns so you can improve your application.

When developing an Android application, you may tend to write most of the code (including business logic) in activities or fragments. This will make your project hard to test...

Technical requirements

The complete code for all the exercises and the activity in this chapter is available on GitHub at https://packt.link/PZNNT

Getting started with MVVM

MVVM allows you to separate the UI and business logic. When you need to redesign the UI or update the Model/business logic, you only need to touch the relevant component without affecting the other components of your app. This will make it easier for you to add new features and test your existing code. MVVM is also useful in creating huge applications that use a lot of data and views.

With the MVVM architectural pattern, your application will be grouped into three components:

• Model: This represents the data layer
• View: This is the UI that displays the data
• ViewModel: This fetches data from Model and provides it to View

The MVVM architectural pattern can be understood better through the following diagram:

Figure 15.1 – The MVVM architectural pattern

The Model contains the data of the application. The activities, fragments, and layouts that your users see and interact with are the Views in MVVM....

Using Retrofit and Moshi

When connecting to your remote network, you can use Retrofit. Retrofit is an HTTP client that makes it easy to implement creating requests and retrieving responses from your backend server.

You can add Retrofit to your project by adding the following code to your app/build.gradle file dependencies:

implementation 'com.squareup.retrofit2:retrofit:2.9.0'

You can then convert the JSON response from Retrofit by using Moshi, a library for parsing JSON into Java objects. For example, you can convert the JSON string response from getting the list of movies into a ListofMovie object for display and storage in your app.

You can add the Moshi Converter to your project by adding the following code to your app/build.gradle file dependencies:

implementation 'com.squareup.retrofit2:
converter-moshi:2.9.0'

In your Retrofit builder code, you can call addConverterFactory and pass Moshi ConverterFactory:

Retrofit.Builder()
  ...

Using WorkManager

WorkManager is a Jetpack library for background operations that can be delayed and can run based on the constraints you set. It is ideal for doing something that must be run but can be done later or at regular intervals, regardless of whether the app is running or not.

You can use WorkManager to run tasks such as fetching the data from the network and storing it in your database at scheduled intervals. WorkManager will run the task even if the app has been closed or if the device restarts. This will keep your database up to date with your backend.

You can add WorkManager to your project by adding the following code to your app/build.gradle file dependencies:

implementation 'androidx.work:work-runtime:2.7.1'

WorkManager can call the repository to fetch and store data from either the local database or the network server.

Let’s try adding WorkManager to an Android project.

Exercise 15.03 – adding WorkManager to an Android Project...

Summary

This chapter focused on architectural patterns for Android. You started with the MVVM architectural pattern. You learned about its three components: the Model, the View, and the ViewModel. You also used data binding to link the View with the ViewModel.

Next, you learned about how the Repository pattern can be used to cache data. Then, you learned about WorkManager and how you can schedule tasks such as retrieving data from the network and saving that data to the database to update your local data.

In the next chapter, you will learn how to improve the look and design of your apps with animations. You will add animations and transitions to your apps with CoordinatorLayout and MotionLayout.