The Android development for this Java project is based in Android Studio. In order to visualize the front end GUI and test backend logics, this project uses the emulator inside Android Studio to display the app outlook. The virtual device configuration for this emulator is baesed on Pixel with Tiramisu API33 as the x86 image.
Figure 1. Frontend software architecture design process flow (click the diagram to view in a larger view)
The main activity xml layout consists of frgament container view (FragmentContainerView) and bottom navigation view (BottomNavigationView) as the overall front-end GUI architecture. The FragmentContainerView contains a navigation graph which connects all the app fragments (home, search, save, details). The navigation graph is managed by navigation controller to switch with different fragments. The NavigationUI setups the navigation controller (NavController) and bottom navigation view (BottomNavigationView) together so that the correspondin fragment will be displayed on screen when user clicks a specific tab inside bottom navigation view. Each tab id and associated fragment id inside navigation graph should be matched up so that navigation controller (NavController) can find the fragment and display it on the
frgament container view (FragmentContainerView).
The backend software design for this Android application development follows the MVVM (Data Model-View-View Model) design architecture.
The data model is the layer of retrieving Article data sources either from local Room DB (more discussion on database section) or cloud service. In order to access the external service in a convenient manner, this project utilizes of Retrofit client as the endpoint to retreiving data by NewsAPI. The Retrofit client is an upper layer to hide the complexity of HTTP request/response, developer can just use the NewsAPI created from Retrofit client builder to access external data. This project wraps up both the database query and external API calls into a repository called NewsRepository so that developer can just use this instance to access data rather than directly request data in a lower level.
The view is the layer of displaying data source in a Fragment manner. A Fragment typically consists of View and Adapter. Based on different product fuctional requirement, the View can be CardStackView, RecycleView, ScrollView etc. Those Views are generated through view binding which binds the view from XML layout to Java object field. The Adapter is used to generate ViewHolder (view binding from item view XML layout) and binds the data source to those ViewHolders.
There is a Manager inside View to manage the life cycle of ViewHolders generated from Adapter. Therefore, developer needs to pass Adapter and Manager to View in each Fragment.
In order to connect the view layer and data model layer together, there is a middle layer called view model. The ViewModel for each different Fragment is generated
in a factory builder design pattern through NewsViewModelFactory, which provides the NewsRepository to each ViewModel so that the data source can be shared to view layer. The ViewModel gets data through calling NewsRepository and wait/observe the data response. Since the data response is wrapped inside LiveData<T>, ViewModel can observe it. Once the data response appears, Adapter will sync the data response to its inner data field and call notifyDataSetChanged(), which will
trigger the ViewHolder to re-bind the new data source so that view layer can be updated.
The home page displays the news article data in a card stack view with like/unlike buttons underneath it. Users can like/unlike an article, the liked articles will be saved into Room DB. Since saving data/DB query is a relative heavy task, this project uses other thread (not main thread/GUI thread)to do this task in an asyncrhonized manner so that the GUI thread is no blocking from other user actions. The asynced tasks will be put under a message queue maintained by looper, the available thread will pick up the task from the message queue through handler. Unlike Retrofit infrastructure providing Call<T> wrapper for asynced tasks inside NewsAPI, the Room DB layer does not provide such similar structure, developer needs to create asynced task class from AsyncTask and manually do it.
The HomeFragment inherits from CardStackListener so that it can act as a listener to the like/unlike button click events. When user triggers such event, the Manager will notify HomeFragment and it can do the data saving process mentiioned above.
The search page displays the data response from user searching request in a recycle view. The news search view also needs to set a listener to listen for user searching request event. Once the event triggers, the SearchFragment will ask SearchViewModel to retrieve news data source through external NewsAPI. As mentioned
above, the Retrofit infrastructure provides Call<T> wrapper for asynced tasks inside NewsAPI, it will process the task in other thread (not main thread/GUI thread) as well.
The save page displays all the liked news article from user, the liked news artitlces will be retrieved through Room DB query. If user unlikes an article in this page,
there is also an asynced task to delete this article through Room DB query. Since the articles are wrapped inside LiveData<T>, the SaveVideModel observes the update of articles, SavedNewsAdapter will sync the data response to its inner data field and call notifyDataSetChanged(), which will trigger the ViewHolder to re-bind the new data source so that view layer can be updated.
The details page shows the details of an article if user clicks an article either in search page or save page. It only contains a scrollview. The SearchFragment needs to implement the ItemCallback interface inside SearchNewsAdapterwhich containes the callback method for switching to details fragment. The same logic applies
to the save page.
Similar to Hibernate in Spring MVC framework, Room is an annotaion based ORM solution for SQLite data query on Android platform. The Room DB creates the TinnewsDatabase which uses ArticleDao data access object to do SQLite data query. The entity of data is exposed as a Java object on developer side, which makes the
data query more convenient so that developer does not need to use SQL language to access database. The schema for an article entity shows below:
Figure 3. RDBMS schema (article)