Migration to Model-View-ViewModel Architecture and LiveData in Open Event Organizer App

Open Event Organizer App (Eventyay Organizer App) is the Android app used by event organizers to create and manage events on the Eventyay platform as well as check-in and check-out attendees along with other functionalities. The app used the MVP (Model-View-Presenter) architecture and is being ported to MVVM (Model-View-ViewModel). This article will explain the procedure of migrating MVP to MVVM architecture and implementing LiveData. 

Why migrate to MVVM?

The MVVM architecture is designed to store and manage UI-related data in a lifecycle conscious way. Configuration changes such as screen rotations are handled properly by ViewModels.

Tight Coupling:

The issue of tight coupling is resolved since only the View holds the reference to ViewModel and not vice versa. A single View can hold references to multiple ViewModels.

Testability:

Since Presenters are hard bound to Views, writing unit tests becomes slightly difficult as there is a dependency of a View.

ViewModels are more unit test friendly as they can be independently tested. There is no dependency of the View.

Here, the implementation is being described with the example of About Event module in the Open Event Organizer App.

First step is the creation of a new class AboutEventViewModel which extends ViewModel.

@Binds
@IntoMap
@ViewModelKey(AboutEventViewModel.class)
public abstract ViewModel bindAboutEventViewModel(AboutEventViewModel aboutEventViewModel);

The new ViewModel has to be added to the ViewModelModule:

Constructor for the ViewModel:

@Inject
public AboutEventViewModel(EventRepository eventRepository,  CopyrightRepository copyrightRepository,
DatabaseChangeListener<Copyright> copyrightChangeListener) {
    this.eventRepository = eventRepository;
    this.copyrightRepository = copyrightRepository;
    this.copyrightChangeListener = copyrightChangeListener;

    eventId = ContextManager.getSelectedEvent().getId();
}

We are using Dagger2 for dependency injection. 

LiveData

LiveData is a lifecycle-aware data holder with the observer pattern.

When we have a LiveData object (e.g. list of attendees), we can add some LifecycleOwner (it can be Activity or Fragment) as an observer. Using this:

The Activity or Fragment will remain updated with the data changes.

Observers are only notified if they are in the STARTED or RESUMED state which is also known as the active state. This prevents memory leaks and NullPointerExceptions because inactive observers are not notified about changes.

Now, let’s discuss about the implementation of LiveData. We will create objects of SingleEventLiveData<> class.

private final SingleEventLiveData<Boolean> progress = new SingleEventLiveData<>();
private final SingleEventLiveData<String> error = new SingleEventLiveData<>();
private final SingleEventLiveData<Event> success = new SingleEventLiveData<>();
private final SingleEventLiveData<Copyright> showCopyright = new SingleEventLiveData<>();
private final SingleEventLiveData<Boolean> changeCopyrightMenuItem = new SingleEventLiveData<>();
private final SingleEventLiveData<String> showCopyrightDeleted = new SingleEventLiveData<>();

The functions to get the LiveData objects:

public LiveData<Boolean> getProgress() {
    return progress;
}

public LiveData<Event> getSuccess() {
    return success;
}

public LiveData<String> getError() {
    return error;
}

public LiveData<Copyright> getShowCopyright() {
    return showCopyright;
}

public LiveData<Boolean> getChangeCopyrightMenuItem() {
    return changeCopyrightMenuItem;
}

public LiveData<String> getShowCopyrightDeleted() {
    return showCopyrightDeleted;
}

Now, we can remove getView() methods and instead, these objects will be used to call various methods defined in the fragment.

Let’s discuss the changes required in the AboutEventFragment now.

The Fragment will have ViewModelProvider.Factory injected.

@Inject
ViewModelProvider.Factory viewModelFactory;

Declare an object of the ViewModel.

private AboutEventViewModel aboutEventViewModel;

Then, in onCreateView(), viewModelFactory will be passed to the ViewModelProviders.of() method as the factory, which is the second parameter.

aboutEventViewModel = ViewModelProviders.of(this, viewModelFactory).get(AboutEventViewModel.class);

Replace all references to the Presenter with references to the ViewModel.

Add the Fragment as an observer to the changes by adding the following in the onStart() method:

aboutEventViewModel.getProgress().observe(this, this::showProgress);
aboutEventViewModel.getSuccess().observe(this, this::showResult);
aboutEventViewModel.getError().observe(this, this::showError);
aboutEventViewModel.getShowCopyright().observe(this, this::showCopyright);
aboutEventViewModel.getChangeCopyrightMenuItem().observe(this, this::changeCopyrightMenuItem);
aboutEventViewModel.getShowCopyrightDeleted().observe(this, this::showCopyrightDeleted);

Two parameters are passed to the observe() method  –  first one is LifecycleOwner, which is our Fragment in this case. The second one is a callback along with a parameter and is used to call the required method.

With this, the implementation of MVVM and LiveData is brought to completion.

Resources:

Documentation: ViewModel, LiveData

Further reading:

Open Event Organizer App: Project repo, Play Store, F-Droid

Continue Reading Migration to Model-View-ViewModel Architecture and LiveData in Open Event Organizer App

Handle app links and apply unit tests in Open Event Attendee Application

The open event attendee is an android app which allows users to discover events happening around the world using the Open Event Platform. It consumes the APIs of the open event server to get a list of available events and can get detailed information about them. Users following links on devices have one goal in mind: to get to the content they want to see. As a developer, you can set up Android App Links to take users to a link’s specific content directly in your app, bypassing the app-selection dialog, also known as the disambiguation dialog. Because Android App Links leverage HTTP URLs and association with a website, users who don’t have your app installed go directly to content on your site.

A unit test generally exercises the functionality of the smallest possible unit of code (which could be a method, class, or component) in a repeatable way. You should build unit tests when you need to verify the logic of specific code in your app.

  • Why unit test cases?
  • Setup app link intent in the app
  • Apply unit test cases
  • Conclusion
  • Resources

Let’s analyze every step in detail.

Why unit test cases?

As it is already discussed what the app link intents are, and it is basically for providing a better user experience for the application. These are some following reason why unit test cases should use – 

  1. Rapid feedback on failures.
  2. Early failure detection in the development cycle.
  3. Safer code refactoring, letting you optimize code without worrying about regressions.
  4. Stable development velocity, helping you minimize technical debt.

JUnit4 library is used for unit tests.

Setup app link intent in the app

Declare the frontend host according to build flavor in the app level gradle file:

buildTypes {
        release {
            resValue "string",  "FRONTEND_HOST", "eventyay.com"
        }
        debug {
            resValue "string", "FRONTEND_HOST", "open-event-fe.netlify.com"
        }
    }

Handle the app link intent in Manifest file by adding intent filter under main activity decleartion:

<intent-filter>
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.DEFAULT" />
    <category android:name="android.intent.category.BROWSABLE" />

    <data
        android:scheme="https"
        android:host="@string/FRONTEND_HOST"/>
</intent-filter>

Manifest will through the intent in the main activity file.

Now handle the intent in main activity:

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        handleAppLinkIntent(intent)
    }

    override fun onNewIntent(intent: Intent?) {
        super.onNewIntent(intent)
        handleAppLinkIntent(intent)
    }

    private fun handleAppLinkIntent(intent: Intent?) {
        val uri = intent?.data ?: return
        val bundle = AppLinkUtils.getArguments(uri)
        val destinationId = AppLinkUtils.getDestinationId(uri)
        if (destinationId != null) {
            navController.navigate(destinationId, bundle)
        }
    }

Here a new class/object AppLinkUtils is defined which will return destination fragment id and the argument/data according to the intent URI.

Apply unit test cases:

First, implement the libraries in the gradle file –  1. JUnit for unit tests, 2. Robolectric for using android classes in the test class:

testImplementation 'junit:junit:4.12'
testImplementation 'org.robolectric:robolectric:3.4.2'

Create a test class for testing the app link functions and run it with RoboLectricTestRunner:

private const val EVENT = "event"
private const val RESET_PASSWORD = "resetPassword"
private const val VERIFY_EMAIL = "verifyEmail"

@RunWith(RobolectricTestRunner::class)
class AppLinkUtilsTest {

    private fun getAppLink(type: String): Uri {
        return when (type) {
            EVENT -> Uri.parse("https://eventyay.com/e/5f6d3feb")
            RESET_PASSWORD -> Uri.parse("https://eventyay.com/reset-password?token=822980340478781748445098077144")
            VERIFY_EMAIL -> Uri.parse("https://eventyay.com/verify?token=WyJsaXZlLmhhcnNoaXRAaG")
            else -> Uri.parse("")
        }
    }

    @Test
    fun `should get event link`() {
        val uri = getAppLink(EVENT)
        assertEquals(R.id.eventDetailsFragment, AppLinkUtils.getDestinationId(uri))
        assertEquals("""
            5f6d3feb
        """.trimIndent(), AppLinkUtils.getArguments(uri).getString(EVENT_IDENTIFIER))
    }// Find more test cases in the GitHub Repo.

Testing response:

GIF

In a Nutshell

So, essentially the Eventyay Attendee should have this feature to handle all links i.e. Reset password, verify user email and open event details in the app itself. So, we can provide a better user experience in-app instead of redirecting to the frontend for them.

Resources

  1. Android app links: https://developer.android.com/studio/write/app-link-indexing
  2. Developing android unit testing: https://www.vogella.com/tutorials/AndroidTesting/article.html

Tags

Eventyay, open-event, JUnit, AndroidUnitTest, AppLinks, Fossasia, GSoC, Android, Kotlin

Continue Reading Handle app links and apply unit tests in Open Event Attendee Application

Configure location feature using MVVM in Open Event Attendee Application

The open event attendee is an android app which allows users to discover events happening around the world using the Open Event Platform. It consumes the APIs of the open event server to get a list of available events and can get detailed information about them. It deals with events based on location, but we have to take the location as an input from the user. While in many cases, we have to search for events on our current location only. To make this work, I have added a current location option, where the app will get our location and search for nearby events. Earlier we had to enter our current location as well to search nearby events.

Model–view–viewmodel is a software architectural pattern. MVVM facilitates separation of development of the graphical user interface – be it via a markup language or GUI code – from the development of the business logic or back-end logic (the data model).

  • Why Model-view-ViewModel?
  • Setup Geo location View Model
  • Configure location feature with MVVM
  • Conclusion
  • Resources

Let’s analyze every step in detail.

Advantages of using Model-view-ViewModel

  1. A clean separation of different kinds of code should make it easier to go into one or several of those more granular and focused parts and make changes without worrying.
  2. External and internal dependencies are in separate pieces of code from the parts with the core logic that you would like to test.
  3. Observation of mutable live data whenever it is changed.

Setup the Geolocation view model

Created new kotlin class name GeoLocationViewModel which contains a configure function for current location:

package org.fossasia.openevent.general.search

class GeoLocationViewModel : ViewModel() {
    fun configure(activity: Activity) { }                                     
}

The GeoLocationViewModel class implement as VIewModel().

Now add the class in module inside Modules.kt :

val viewModelModule = module {
    viewModel { GeoLocationViewModel() }
}

Configure location feature with GeoLocationViewModel:

First, add play store location service implementation inside dependencies of build.gradle:

// Location Play Service
playStoreImplementation 'com.google.android.gms:play-services-location:16.0.0'

Now we need location permissions to implement this feature. Adding user permissions in the manifest file:

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

Now ask user for the location permission:

private fun checkLocationPermission() {
        val permission = context?.let {
            ContextCompat.checkSelfPermission(it, Manifest.permission.ACCESS_COARSE_LOCATION) }
        if (permission != PackageManager.PERMISSION_GRANTED) {
            requestPermissions(arrayOf(Manifest.permission.ACCESS_COARSE_LOCATION,
                Manifest.permission.ACCESS_FINE_LOCATION), LOCATION_PERMISSION_REQUEST)
        }
    }

Check for device location is enabled, if not send an intent to turn location on. The method is written inside configure function:

val service = activity.getSystemService(Context.LOCATION_SERVICE)
        var enabled = false
        if (service is LocationManager) enabled = service.isProviderEnabled(LocationManager.NETWORK_PROVIDER)
        if (!enabled) {
            val intent = Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS)
            activity.startActivity(intent)
            return
        }

Now create Mutable live data for current location inside the view model class :

private val mutableLocation = MutableLiveData<String>()
val location: LiveData<String> = mutableLocation

Now implement location request and location callback inside configure method:

val locationRequest: LocationRequest = LocationRequest.create()
locationRequest.priority = LocationRequest.PRIORITY_LOW_POWER
val locationCallback = object : LocationCallback() {
      override fun onLocationResult(locationResult: LocationResult?) {
           if (locationResult == null) {
               return
            }
            for (location in locationResult.locations) {
                if (location != null) {
                    val latitude = location.latitude
                    val longitude = location.longitude
                    try {
                        val geocoder = Geocoder(activity, Locale.getDefault())
                        val addresses: List<Address> = geocoder.getFromLocation(latitude, longitude, maxResults)
                        for (address: Address in addresses) {
                            if (address.adminArea != null) {
                                mutableLocation.value = address.adminArea
                            }
                        }
                    } catch (exception: IOException) {
                        Timber.e(exception, "Error Fetching Location")
                    }
                }
             }
        }
    }

Now call location service inside configure method:

LocationServices
                .getFusedLocationProviderClient(activity)
                .requestLocationUpdates(locationRequest, locationCallback, null)

Now observe data for current location inside the fragment from the view model. Save the current user location and go to the main activity:

private val geoLocationViewModel by viewModel<GeoLocationViewModel>()
geoLocationViewModel.location.observe(this, Observer { location ->
                searchLocationViewModel.saveSearch(location)
                redirectToMain()
            })

GIF

In a Nutshell

So, essentially the Eventyay Attendee should have this feature to show all the events nearby me or in my city, although the app was already doing the job, but we had to manually select the city or locality we wish to search, now after the addition of dedicated current location option, the app will be more user friendly and automated.

Resources

  1. Google location services API: https://www.toptal.com/android/android-developers-guide-to-google-location-services-api
  2. MVVM architecture in Android: https://proandroiddev.com/mvvm-architecture-viewmodel-and-livedata-part-1-604f50cda1

Tags

Eventyay, open-event, PlayServices, Location, MVVM, Fossasia, GSoC, Android, Kotlin

Continue Reading Configure location feature using MVVM in Open Event Attendee Application

Serializing Java objects for REST API Requests in Open Event Organizer App

Open Event Organizer App is a client side application which uses REST API for network requests. The server supports sending and receiving of data only in JSONAPI spec, so, we needed to serialize java models into JSON objects and deserialize JSON data into java models following JSONAPI spec. To achieve this we followed the following steps.

Specifications

We will be using jasminb/jsonapi-converter which handles request/response parsing of models following JSONAPI Spec and Retrofit plugin of jackson converter to serializing JSON to Java Models and vice versa.

Let’s create a java model. We are using some annotations provided by Lombok library to avoid writing boilerplate code. @JsonNaming annotation is used to apply KebabCaseStrategy while serializing fields

@Data
@Type(“order”)
@AllArgsConstructor
@JsonNaming(PropertyNamingStrategy.KebabCaseStrategy.class)
@Table(database = OrgaDatabase.class, allFields = true)
public class Order {

@PrimaryKey
@Id(LongIdHandler.class)
public Long id;

public float amount;
public String completedAt;
public String identifier;
public String paidVia;
public String paymentMode;
public String status;

@Relationship(“event”)
@ForeignKey(stubbedRelationship = true, onDelete = ForeignKeyAction.CASCADE)
public Event event;

public Order() { }
}

In the NetworkModule class, there is a method providesMappedClasses() containing a list of classes that needs to be serialized/deserialized. We need to add the above model in the list. Then, this list is provided to Singleton instance of JSONAPIConvertorFactory through Dagger. JSONAPIConvertorFactory uses the Retrofit ObjectMapper and maps the classes that are handled by this instance.

@Provides
Class[] providesMappedClasses() {
return new Class[]{Event.class, Attendee.class, Ticket.class, Order.class};
}

Further, various serialization properties can be used while building Singleton ObjectMapper instance. Adding any properties here ensures that these are applied to all the mapped classes by JSONAPIConvertorFactory. For eg, we are using the serialization property to throw an exception and fail whenever empty beans are encountered.

@Provides
@Singleton
ObjectMapper providesObjectMapper() {
return new ObjectMapper()
.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS)
// Handle constant breaking changes in API by not including null fields
// TODO: Remove when API stabilizes and/or need to include null values is there
.setSerializationInclusion(JsonInclude.Include.NON_ABSENT);
}

Resources

  1. Github Repository for jsonapi-converter https://github.com/jasminb/jsonapi-converter
  2. Github repository for Jackson Retrofit Plugin https://github.com/square/retrofit/tree/master/retrofit-converters/jackson
  3. Official Website for Project Lombok https://projectlombok.org/

Github Repository for Open-Event-Orga-App https://github.com/fossasia/open-event-orga-app

Continue Reading Serializing Java objects for REST API Requests in Open Event Organizer App

Adding Preference Settings using Preference Fragment Compat

It is very much likely that one needs to add preferences to their app which span the entire application and therefore can be accessed anywhere in the app without storing anything in database or making global variables. For an instance, in Open Event Organizer App we added the preferences to store the privacy policy, cookie policy etc. The user can access these items in Settings Preference which in device settings. In this blog post we will see how to add preference settings to the app by storing the data in shared preferences.

Specifications

The benefit of storing the data in shared preference and not in local storage is that the access time for the data is drastically reduced and the data persists even when the app is closed. We will use this library which is built on top of official preference-v7 library.

Firstly, we will make a preference resource layout file and add the preference for privacy policy and cookie policy in the preference screen.

<PreferenceScreen xmlns:android=”http://schemas.android.com/apk/res/android”>

<Preference
android:key=”@string/privacy_policy_key”
android:title=”@string/privacy_policy” />

<Preference
android:key=”@string/cookie_policy_key”
android:title=”@string/cookie_policy” />

</PreferenceScreen>

Make a separate preference fragment class named LegalPreferenceFragment which extends PreferenceFragmentCompat. Then we will override onCreatePreferenceFix() method.

Inside this, we will create an instance of Preference Manager and set shared preference name for it and set the preference using the layout file. This enables us to use findPreference() method to retrieve the layout preferences by their key. After, retrieving the preference we will set onClick listener to launch activity with an intent to open browser for the url passed in data bundle.

@Override
public void onCreatePreferencesFix(@Nullable Bundle bundle, String rootKey) {
PreferenceManager manager = getPreferenceManager();
manager.setSharedPreferencesName(Constants.FOSS_PREFS);

setPreferencesFromResource(R.xml.legal_preferences, rootKey);

findPreference(getString(R.string.privacy_policy_key)).setOnPreferenceClickListener(preference -> {
BrowserUtils.launchUrl(getContext(), PRIVACY_POLICY_URL);
return true;
});
findPreference(getString(R.string.cookie_policy_key)).setOnPreferenceClickListener(preference -> {
BrowserUtils.launchUrl(getContext(), COOKIE_POLICY_URL);
return true;
});
}

References

  1. Preference Fragment Compat library by Takisoft https://github.com/Gericop/Android-Support-Preference-V7-Fix
  2. Android Preference Documentation https://developer.android.com/reference/android/preference/PreferenceGroup
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Implementing Timeline for Attendees Activity in Organizer App

Open Event Organizer App offers the functionality to Checkin/checkout attendees but the Organizer was unable to view when a particular attendee was checkin or checkout. We decided to implement a feature to view the timeline of checkin/checkout for each attendee.

Let’s begin by adding the dependency in build.gradle.

implementation “com.github.vipulasri:timelineview:”1.0.6”

In the recyclerview item layout add the TimeLineView layout. Following are some of the useful attributes.

  1. app:markerInCenter – This defines the position of the round marker within the layout. Setting it to true, position it in center.
  2. app:marker – Custom drawables can be set as marker.
<com.github.vipulasri.timelineview.TimelineView
android:id=”@+id/time_marker”
android:layout_width=”wrap_content”
android:layout_height=”match_parent”
app:marker=”@drawable/ic_marker_active”
app:line=”#aaa4a4″
app:lineSize=”2dp”
app:linePadding=”3dp”
app:markerInCenter=”true”
app:markerSize=”20dp” />

The ViewHolder class will extend the RecyclerView,ViewHolder class. In the constructor, we will add a parameter viewType and then set it to TimeLine Marker layout using method initLine.

public CheckInHistoryViewHolder(CheckInHistoryLayoutBinding binding, int viewType) {
super(binding.getRoot());
this.binding = binding;
binding.timeMarker.initLine(viewType);
}

In RecyclerViewAdapter, we will override the getItemViewType() method. Here we will use the getTimeLineViewType method which takes in position and total size of the recycler view list and returns a TimeLineView type object.

@Override
public int getItemViewType(int position) {
return TimelineView.getTimeLineViewType(position, getItemCount());
}

References

  1. TimeLineView library by VipulAsri https://github.com/vipulasri/Timeline-View
  2. Android Documentation for RecyclerViewAdapter https://developer.android.com/reference/android/support/v7/widget/RecyclerView.Adapter
  3. Android Documentation for RecyclerViewView https://developer.android.com/reference/android/support/v7/widget/RecyclerView
Continue Reading Implementing Timeline for Attendees Activity in Organizer App

Adding List Preference Settings using Preference Fragment Compat

In this blog post we will see how we can add a Preference List in Settings which will display a list of radio buttons in UI which user can choose from. In Open Event Orga App, the Organizer had a choice to switch between viewing Net Sales or Gross Sales in the App’s Dashboard. We decided to use a preference list to allow the user to select between using Net or Gross Sales.

The benefit of using Preference List and not any other storage media (like SQLite) to store the information is that, Preference List stores the information as key-value pair in SharedPreferences which makes it easy to store and extract small amount of data with strong consistency guarantees and using less time. Let’s move on to the implementation.

Implementation

Firstly add the dependency in build.gradle.

implementation “com.takisoft.fix:preference-v7:27.1.0.0”

In the preferences layout file, we will use checkboxes.

<PreferenceScreen xmlns:android=”http://schemas.android.com/apk/res/android”>

<CheckBoxPreference
android:key=”@string/gross_sales_key”
android:title=”@string/gross_sales”
android:defaultValue=”true” />

<CheckBoxPreference
android:key=”@string/net_sales_key”
android:title=”@string/net_sales”
android:defaultValue=”false” />
</PreferenceScreen>

We will create SalesDataSettings class which extends PreferenceFragmentCompat and override onCreatePreferenceFix method. We will request PreferenceManager and set SharedPreferencesName. The manager will be used to store and retrieve key-value pairs from SharedPreferences. Using setPreferencesFromResource we will attach the layout file to the fragment.

PreferenceManager manager = getPreferenceManager();
manager.setSharedPreferencesName(Constants.FOSS_PREFS);

setPreferencesFromResource(R.xml.sales_data_display, rootKey);

We are using CheckBox Preferences and modifying their behaviour to work as a Radio Preference List because Radio reference is not provided by Android. We are initializing two checkboxes and attaching a preference listener to unset all other checkboxes which one is selected.

CheckBoxPreference netSales = (CheckBoxPreference) findPreference(NET_SALES);
CheckBoxPreference grossSales = (CheckBoxPreference) findPreference(GROSS_SALES);

Preference.OnPreferenceChangeListener listener = (preference, newValue) -> {
String key = preference.getKey();

switch (key) {
case GROSS_SALES:
netSales.setChecked(false);
break;
case NET_SALES:
grossSales.setChecked(false);
break;
default:
break;
}
return (Boolean) newValue;
};

netSales.setOnPreferenceChangeListener(listener);
grossSales.setOnPreferenceChangeListener(listener);

We can load SalesDataDisplay Fragment class when a preference button is clicked using fragment transactions as shown below.

findPreference(getString(R.string.sales_data_display_key)).setOnPreferenceClickListener(preference -> {
getFragmentManager().beginTransaction()
.replace(R.id.fragment_container, SalesDataSettings.newInstance())
.addToBackStack(null)
.commit();
return true;
});

References

  1. Shared Preferences Documentation https://developer.android.com/reference/android/content/SharedPreferences
  2. Gericop Takisoft Android-Support-Preference-V7-Fix https://github.com/Gericop/Android-Support-Preference-V7-Fix
  3. Codebase for Open Event Organizer App https://github.com/fossasia/open-event-orga-app
Continue Reading Adding List Preference Settings using Preference Fragment Compat

Performing Database Migrations using DbFlow

In Open Event Organizer Android App we decided to add database migrations for every change in database while development. Two of the reasons behind this –

  1. The users have some version of the app installed and then during development the developers had to modify the database, let’s say, add a table or modify existing ones. This makes the existing database incompatible with the new app. On adding database migration the upgradation of database takes place automatically and prevent the situation of reinstalling the app.
  2. Migrations makes it possible to rollback or upgrade to some particular database state. Thus, help in debugging certain changes in isolation.

Let’s discuss the implementation details. Consider the scenario when a user adds a new table named SpeakersCall. For creating migration for this change we need to add migration class inside OrgaDatabase class annotated with @Database. We will break it down to look closely at each step.

  1. Use @Migration annotation in DbFlow library and specify the new database version (by incrementing the existing version) and the database class.
  2. Extend BaseMigration and override migrate method.
  3. The logic used inside the migrate method can be different for different tasks. In the present case we first need to delete any existing table (if exists) with the name SpeakersCall and then recreate that table in database.
  4. Create an array of java classes which are created/modified.
  5. We wrap the SQL query inside a Database Wrapper class which prevents it from running recursively.
  6. FlowManager uses reflection to look up and construct the generated database holder class used in defining the structure for all databases used in this application. So we will getModelAdapter for the class to be recreated and use creation query returned by Model Adapter and execute it.
@Migration(version = 15, database = OrgaDatabase.class)
public static class MigrationTo15 extends BaseMigration {

@Override
public void migrate(@NonNull DatabaseWrapper databaseWrapper) {
Timber.d(“Running migration for DB version 14”);

Class<?>[] recreated = new Class[] {SpeakersCall.class};

for (Class<?> recreate: recreated) {
ModelAdapter modelAdapter = FlowManager.getModelAdapter(recreate);
databaseWrapper.execSQL(DROP_TABLE + modelAdapter.getTableName());
databaseWrapper.execSQL(modelAdapter.getCreationQuery());
}
}
}

Similarly, we can write migration for changing a column of table(s).

Continue Reading Performing Database Migrations using DbFlow

Testing the ViewModels in Open Event Organizer App

In Open Event Organizer Android App we follow Test Driven Development Approach which means the features added in the app are tested thoroughly by unit tests. More tests would ensure better code coverage and fewer bugs. This blog explains how to write tests for Viewmodel class in MVVM architecture.

Specifications

We will use JUnit4 to write unit tests and Mockito for creating mocks. The OrdersViewModel class returns the list of Order objects to the Fragment class. The objects are requested from OrderRepository class which fetches them from Network and Database. We will create a mock of OrderRepository class since it is out of context and contain logic that doesn’t depend on Orders Respository. Below is the getOrders method that we will test.

 public LiveData<List<Order>> getOrders(long id, boolean reload) {
if (ordersLiveData.getValue() != null && !reload)
return ordersLiveData;

compositeDisposable.add(orderRepository.getOrders(id, reload)
.compose(dispose(compositeDisposable))
.doOnSubscribe(disposable -> progress.setValue(true))
.doFinally(() -> progress.setValue(false))
.toList()
.subscribe(ordersLiveData::setValue,
throwable -> error.setValue(ErrorUtils.getMessage(throwable).toString())));

return ordersLiveData;
}

We will be using InstantTaskExecutorRule() which is a JUnit Test Rule that swaps the background executor used by the Architecture Components with a different one which executes each task synchronously. We will use setUp() method to load the RxJavaPlugins, RxAndroid plugins and reset them in tearDown method which will ensure each test runs independently from the other and avoid memory leaks. After doing this initialization and basic setup for tests we can begin code the method shouldLoadOrdersSuccessfuly() to test the getOrders method present in ViewModel class. Let’s see the step by step approach.

  1. Use Mockito.when to return Observables one by one from ORDERS_LIST whenever the method getOrders of the mock orderRepository is called.
  2. We will use Mockito.InOrder and pass orders, orderRepository and progress to check if they are called in a particular order.
  3. We will use .observeForever method to observe on LiveData objects and add a ArrayList on change.
  4. Finally, we will test and verify if the methods are called in order.
@Test
public void shouldLoadOrdersSuccessfully() {
when(orderRepository.getOrders(EVENT_ID, false))
.thenReturn(Observable.fromIterable(ORDERS_LIST));

InOrder inOrder = Mockito.inOrder(orders, orderRepository, progress);

ordersViewModel.getProgress().observeForever(progress);

orders.onChanged(new ArrayList<>());

ordersViewModel.getOrders(EVENT_ID, false);

inOrder.verify(orders).onChanged(new ArrayList<>());
inOrder.verify(orderRepository).getOrders(EVENT_ID, false);
inOrder.verify(progress).onChanged(true);
inOrder.verify(progress).onChanged(false);
}

Similar approach can be followed for writing tests to check other behaviour of the ViewModel.

References

  1. Official Documentation for testing. https://developer.android.com/reference/android/arch/core/executor/testing/InstantTaskExecutorRule
  2. Official Documentation for JUnit.  https://junit.org/junit4/
  3. Official documentation for Mockito.  http://site.mockito.org/
  4. Open Event Organizer App codebase.  https://github.com/fossasia/open-event-orga-app
Continue Reading Testing the ViewModels in Open Event Organizer App

Swipe to Check In/Out in Open Event Organizer App

Open Event Organizer App didn’t provide any option for the Event Organizer to view the list of Attendees present under an Order and check them in/out the event. Therefore, we designed a system such that the Organizer can just swipe the attendee present under an order to check them in or out. In this blog post, I will discuss how we implemented this functionality in Open Event Organizer App without using any third party libraries.

Specifications

We will create a separate class SwipeController.java which extends ItemTouchHelper.SimpleCallback and provide the swiping functionalities to our plain old recyclerview. We will call the super constructor with ItemTouchHelper.LEFT and ItemTouchHelper.RIGHT as arguments to provide left as well as right movements in each recyclerview list item. The bitmaps and paint object initialized here will be used later in onDraw.

public SwipeController(OrderDetailViewModel orderDetailViewModel, OrderAttendeesAdapter orderAttendeesAdapter, Context context) {
super(0, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT);
this.orderDetailViewModel = orderDetailViewModel;
this.orderAttendeesAdapter = orderAttendeesAdapter;

closeIcon = BitmapFactory.decodeResource(context.getResources(), R.drawable.close);
doneIcon = BitmapFactory.decodeResource(context.getResources(), R.drawable.done);

paintGreen.setColor(context.getResources().getColor(R.color.light_green_500));
paintRed.setColor(context.getResources().getColor(R.color.red_500));
}

Next, we will override getMovementFlags method. This method decides the allowed movement directions for each recyclerview item. The deciding logic is that, if an attendee is checked in then the allowed movement is left to check out and if an attendee is checked out then the allowed movement is right to check in. If neither of the above case, then both movements are allowed.

@Override
public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
int dragFlags = 0;

If (orderDetailViewModel.getCheckedInStatus(

viewHolder.getAdapterPosition()) == null)
makeMovementFlags(dragFlags, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT);

if (orderDetailViewModel.getCheckedInStatus(

viewHolder.getAdapterPosition())) {
return makeMovementFlags(dragFlags, ItemTouchHelper.LEFT);
} else {
return makeMovementFlags(dragFlags, ItemTouchHelper.RIGHT);
}
}

The onChildDraw method involves the code doing actual drawing. The variables used in code are discussed below.

  1. ActionState – Checks the state of the recycler view item. We proceed with the below logic if the item is being swiped.
  2. dX – The distance by which the item is swiped. Positive for left and negative for right.
  3. Background – Background of the viewholder. Rectangular in shape and dimensions changed with change in dX.
  4. IconDest – Calculates the position where the icons (close icon or done icon) is placed in canvas
  5. Canvas – Java Canvas on which the drawing is done. We set the background and draw the bitmaps on their location in canvas.
@Override
public void onChildDraw(Canvas canvas, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder,
float dX, float dY, int actionState, boolean isCurrentlyActive) {
if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
View itemView = viewHolder.itemView;
float height = (float) itemView.getBottom() – (float) itemView.getTop();
float width = height / 3;
RectF background;
Paint paint;
Bitmap icon;
RectF iconDest;

if (dX > 0) {
background = new RectF((float) itemView.getLeft(), (float) itemView.getTop(), dX,
(float) itemView.getBottom());
paint = paintGreen;
icon = doneIcon;
iconDest = new RectF((float) itemView.getLeft() + width,
(float) itemView.getTop() + width, (float) itemView.getLeft() + 2 * width,
(float) itemView.getBottom() – width);
} else {
background = new RectF((float) itemView.getRight() + dX, (float) itemView.getTop(),
(float) itemView.getRight(), (float) itemView.getBottom());
paint = paintRed;
icon = closeIcon;
iconDest = new RectF((float) itemView.getRight() – 2 * width,
(float) itemView.getTop() + width, (float) itemView.getRight() – width,
(float) itemView.getBottom() – width);
}

canvas.drawRect(background, paint);
canvas.drawBitmap(icon, null, iconDest, paint);
}
super.onChildDraw(canvas, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
}

Now after the item is swiped out or in, we need to restore its original state again. For this we override the onSwiped method and call notifyItemChanged(). Also, the changes in UI (showing green side strip for checked in and red side strip for checked out) are done by. We call the toggleCheckin() method in ViewModel to toggle the checking status of the attendee in server and local database.

@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
int position = viewHolder.getAdapterPosition();

orderDetailViewModel.toggleCheckIn(position);
orderAttendeesAdapter.notifyItemChanged(position);
}

Last but not the least, we will override the onMove method to return false. Since we are not supporting drag and drop features therefore this method will never be called.

@Override
public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
return false;
}

Resources

  1. Codebase for Open Event Organizer App https://github.com/fossasia/open-event-orga-app
  2. Official documentation for ItemTouchHelper.SimpleCallback https://developer.android.com/reference/android/support/v7/widget/helper/ItemTouchHelper.SimpleCallback
Continue Reading Swipe to Check In/Out in Open Event Organizer App