/AndroidArchitectureComponent

Android Architecture Component with Room database,View Model and Live Data

Primary LanguageJava

AndroidArchitectureComponent

Android Architecture Component with Room database,View Model and Live Data

This sample showcases the following Architecture Components:

Introduction

Features

This sample contains two screens: a list of delivery and a delivery detail view.

Presentation layer

The presentation layer consists of the following components:

  • A main activity that handles 2 Fragments.
  • A fragment to display the list of delivery.
  • A fragment to display a delivery detail review with google map.

The app uses a Model-View-ViewModel (MVVM) architecture for the presentation layer. Each of the fragments corresponds to a MVVM View. The View and ViewModel communicate using LiveData and the following design principles:

  • ViewModel objects don't have references to activities, fragments, or Android views. That would cause leaks on configuration changes, such as a screen rotation, because the system retains a ViewModel across the entire lifecycle of the corresponding view.
  • ViewModel objects expose data using LiveData objects. LiveData allows you to observe changes to data across multiple components of your app without creating explicit and rigid dependency paths between them.
  • Views, including the fragments used in this sample, subscribe to corresponding LiveData objects. Because LiveData is lifecycle-aware, it doesn’t push changes to the underlying data if the observer is not in an active state, and this helps to avoid many common bugs. This is an example of a subscription:
viewModel.getDeliveryList().observe(this, new Observer<List<DeliveryDataModel>>()
        {
            @Override
            public void onChanged(@Nullable List<DeliveryDataModel> deliveryData)
            {
                // Update the UI.

                deliveryArrayList = (ArrayList<DeliveryDataModel>) deliveryData;

                recyclerViewAdapter.addItems(deliveryArrayList);
            }
        });

Data layer

Room populates the database asynchronously when it's created, via the RoomDatabase#Callback. To simulate low-performance, an artificial delay is added. To let other components know when the data has finished populating, the AppDatabase exposes a LiveData object..

To access the data and execute queries, you use a Data Access Object (DAO). For example, a product is loaded with the following query:

   /**
    * Fetch all delivery item from the database.
    */

   @Query("SELECT * FROM DeliveryDataModel")
   LiveData<List<DeliveryDataModel>> fetchAllData();
   
    /**
    * Counts the number of items in the table.
    *
    * @return The number of delivery list.
    */

   @Query("SELECT * FROM DeliveryDataModel where slNo = :slNo")
   Cursor getDeliveryById(int slNo);

Queries that return a LiveData object can be observed, so when a change in one of the affected tables is detected, LiveData delivers a notification of that change to the registered observers.