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

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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
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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
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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).

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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
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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
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Showing Order Details in Eventyay Organizer Android App

In Open Event Organizer App, the organizer was not able to view the details for the Orders received from attendees for his/her events. So in this blog we’ll see how we implemented this functionality in the Orga App.

Specifications

There is a fragment showing the list of all orders for that event. The user will be able to click on order from the list which will then take the user to another fragment where Order details will be displayed. We will be following MVVM architecture to implement this functionality using REST API provided by Open Event Server. Let’s get started.

Firstly, we will create Order Model class. This contains various fields and relationship attributes to setup the table in database using RazizLabs DbFlow annotations.

Then, We will make a GET request to the server using Retrofit 2  to fetch Order object.

@GET(“orders/{identifier}?include=event”)
Observable<Order> getOrder(@Path(“identifier”) String identifier);

The server will return the Order details in form of a Order object and then we will save it in local  database so that when there is no network connectivity then also we can show data to the user and user can refresh to fetch the latest data from network. The network observable handles fetching data from network and disk observable handles saving data in local database.

@NonNull
@Override
public Observable<Order> getOrder(String orderIdentifier, boolean reload) {
Observable<Order> diskObservable = Observable.defer(() ->
repository
.getItems(Order.class, Order_Table.identifier.eq(orderIdentifier)).take(1)
);

Observable<Order> networkObservable = Observable.defer(() ->
orderApi.getOrder(orderIdentifier)
.doOnNext(order -> repository
.save(Order.class, order)
.subscribe()));

return repository
.observableOf(Order.class)
.reload(reload)
.withDiskObservable(diskObservable)
.withNetworkObservable(networkObservable)
.build();
}

Now, we will make a Fragment class that will bind the layout file to the model in the onCreateView method using DataBindingUtil. Further, we will be observing on ViewModel to reflect changes of Order, Progress and Error objects in the UI in the onStart method of the Fragment.

public class OrderDetailFragment extends BaseFragment implements OrderDetailView {

@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
binding = DataBindingUtil.inflate(inflater, R.layout.order_detail_fragment, container, false);

orderDetailViewModel = ViewModelProviders.of(this, viewModelFactory).get(OrderDetailViewModel.class);

return binding.getRoot();
}

@Override
public void onStart() {
super.onStart();
setupRefreshListener();

orderDetailViewModel.getOrder(orderIdentifier, eventId, false).observe(this, this::showOrderDetails);
orderDetailViewModel.getProgress().observe(this, this::showProgress);
orderDetailViewModel.getError().observe(this, this::showError);
}
}

Next, we will create OrderDetailsViewModel.This is the ViewModel class which interacts with the repository class to get data and the fragment class to show that data in UI.

Whenever the user opens Order details page, the method getOrder() twill be called which will request an Order object from OrderRepository, wrap it in MutableLiveData and provide it to Fragment.

Using MutableLiveData to hold the data makes the data reactive i.e. changes in UI are reflected automatically when the object changes. Further, we don’t have to worry handling the screen rotation as LIveData handles it all by itself.

  public LiveData<Order> getOrder(String identifier, long eventId, boolean reload) {
if (orderLiveData.getValue() != null && !reload)
return orderLiveData;

compositeDisposable.add(orderRepository.getOrder(identifier, reload)
.compose(dispose(compositeDisposable))
.doOnSubscribe(disposable -> progress.setValue(true))
.doFinally(() -> progress.setValue(false))
.subscribe(order -> orderLiveData.setValue(order),
throwable -> error.setValue(ErrorUtils.getMessage(throwable))));

if (!reload) {
getEvent(eventId);
}

return orderLiveData;
}
}

References

  1. Codebase for Open Event Orga App https://github.com/fossasia/open-event-orga-app
  2. Official documentation for LiveData Architecture Component https://developer.android.com/topic/libraries/architecture/livedata
  3. Official Github Repository of Retrofit  https://github.com/square/retrofit
  4. Official Github Repository for RxJava https://github.com/ReactiveX/RxJava
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Share Events in the Open Event Organizer Android App

In the Open Event Organizer Android App, after creating an event the organizer was unable to share it. We handled this challenge and came up with options to share Event with other social media apps. Along with that user can send Email to users containing event description with just a click. All this through a UI that our user will love interacting with. Let’s see how we implemented this.

Specifications

We designed a UI given below which offer four functionalities to the user in a single screen.

  1. The Event Name and Date are shown in the CardView.
  2. User can copy Event External URL by clicking on Copy URL option.
  3. User can send Email containing information about the Event like ( Name, Description, Starting and Ending Date-Time for the Event) via Email by clicking on Email option.
  4. User can share the same information described in point three via other social media/chatting apps etc by clicking on many more option.

The is the Event Model class ia a POJO containing the associated attributes.

We will use Retrofit to fetch Event object from server through a GET request in EventApi class.

@GET(“events/{id}?include=tickets”)
Observable<Event> getEvent(@Path(“id”) long id);

Then we will use the getEvent method of EventRepositoryImpl class to make the request for us using EventApi class and then pass on the Response Event object to the ViewModel by wrapping it in RxJava Observable. We are accepting a boolean field named reload which decdes whether we need to reuse the existing Event object from Local Database  or fetch a new object from server.

@Override
public Observable<Event> getEvent(long eventId, boolean reload) {
Observable<Event> diskObservable = Observable.defer(() ->
repository
.getItems(Event.class, Event_Table.id.eq(eventId))
.filter(Event::isComplete)
.take(1)
);

Observable<Event> networkObservable = Observable.defer(() ->
eventApi
.getEvent(eventId)
.doOnNext(this::saveEvent));

return repository.observableOf(Event.class)
.reload(reload)
.withDiskObservable(diskObservable)
.withNetworkObservable(networkObservable)
.build();
}

In ShareEventVewModel, we are calling the getEvent from EventRepositoryImpl class, construct a LiveData object from it so that UI could observe changes on it. Methods getShareableInformation, getShareableUrl, getShareableSubject provide the shareable information to the UI which is further shared with other apps.

public class ShareEventViewModel extends ViewModel {

protected LiveData<Event> getEvent(long eventId, boolean reload) {
if (eventLiveData.getValue() != null && !reload)
return eventLiveData;

compositeDisposable.add(eventRepository.getEvent(eventId, reload)
.doOnSubscribe(disposable -> progress.setValue(true))
.doFinally(() -> progress.setValue(false))
.subscribe(event -> {
this.event = event;
eventLiveData.setValue(event);
},
throwable -> error.setValue(ErrorUtils.getMessage(throwable))));

return eventLiveData;
}

public String getShareableInformation() {
return Utils.getShareableInformation(event);
}

}

In ShareEventFragment class does the work of binding the UI to the model using data binding. It observes the LiveData objects supplied by presenter and reflect the changes in UI to the LiveData object.

public class ShareEventFragment extends BaseFragment implements ShareEventView {

public void shareEvent() {
Intent shareIntent = new Intent();
shareIntent.setAction(Intent.ACTION_SEND);
shareIntent.putExtra(Intent.EXTRA_TEXT, shareEventViewModel.getShareableInformation());
shareIntent.setType(“text/plain”);
startActivity(Intent.createChooser(shareIntent, getResources().getText(R.string.send_to)));
}

public void shareByEmail() {
Intent shareIntent = new Intent();
shareIntent.setAction(Intent.ACTION_SENDTO);
shareIntent.setType(“message/rfc822”);
shareIntent.setData(Uri.parse(“mailto:”));
shareIntent.putExtra(Intent.EXTRA_SUBJECT, shareEventViewModel.getEmailSubject());
shareIntent.putExtra(Intent.EXTRA_TEXT, shareEventViewModel.getShareableInformation());
try {
startActivity(Intent.createChooser(shareIntent, getResources().getText(R.string.send_to)));
} catch (android.content.ActivityNotFoundException ex) {
ViewUtils.showSnackbar(binding.getRoot(), “There are no email clients installed”);
}
}

public void copyUrlToClipboard() {
ClipboardManager clipboard = (ClipboardManager) getActivity().getSystemService(Context.CLIPBOARD_SERVICE);
String eventUrl = shareEventViewModel.getShareableUrl();
if (eventUrl == null) {
ViewUtils.showSnackbar(binding.getRoot(), “Event does not have a Public URL”);
} else {
ClipData clip = ClipData.newPlainText(“Event URL”, shareEventViewModel.getShareableUrl());
clipboard.setPrimaryClip(clip);
ViewUtils.showSnackbar(binding.getRoot(), “Event URL Copied to Clipboard”);
}
}
}

The layout file contains the Event object bind to the UI using Two way Data Binding. Here is an extract from the layout file. For viewing entire file, please refer here.

References

  1. Official documentation of Retrofit 2.x http://square.github.io/retrofit/
  2. Official documentation for RxJava 2.x https://github.com/ReactiveX/RxJava
  3. Official documentation for ViewModel https://developer.android.com/topic/libraries/architecture/viewmodel
  4. Codebase for Open Event Organizer App https://github.com/fossasia/open-event-orga-app
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Delete Image Permanently from Trashbin in Phimpme App

In the Phimpme Android application, users can perform various operations on the images including renaming an image, sharing images, deleting images from the storage etc. However, with the implementation of the Trash Bin feature in the app, the user is now provided with the option to restore back the deleted images. Whenever the delete operation is performed, the selected images are moved to the Trash Bin and the user has the option to either delete the photos permanently or restoring back the deleted photos by navigating to the Trash bin section. So in this post, I’d be discussing the implementation of permanently deleting image/images from the Trashbin.

Step 1

Firstly, we need to add permanent delete option in the popup menu provided in the itemview in the TrashView section. Every item in the Trashbin section displays a popup menu with two options-restore and delete permanently. The permanent delete option has been implemented in the itemview by adding the following lines of code.

<?xml version=“1.0” encoding=“utf-8”?>
<menu xmlns:android=“http://schemas.android.com/apk/res/android” xmlns:app=“http://schemas.android.com/apk/res-auto”>

<item
    android:id=“@+id/delete_permanently”
    android:title=“@string/delete_permanently”
    app:showAsAction=“never” />
</menu>

Step 2

Now when the user opts to permanently delete any photo from the bin, a function deletePermanent would be invoked passing-in the trashbin object corresponding to the selected item as the parameter. Inside the deletePermanent method, a check is performed to determine whether the corresponding image file exists or not using the .exists method of the File class and if the result is true the file is deleted permanently using the .delete method of the File class. The method deletePermanent returns a boolean value depending on whether the image file is deleted permanently from the storage or not. The code snippets used to implement the deletePermanent method is provided below.

private boolean deletePermanent(TrashBinRealmModel trashBinRealmModel){
  boolean succ = false;
  String path = trashBinRealmModel.getTrashbinpath();
  File file = new File(Environment.getExternalStorageDirectory() + “/” + “.nomedia”);
  //File file = new File(Environment.getExternalStorageDirectory() + “/” + “TrashBin”);
  if(file.exists()){
      File file1 = new File(path);
      if(file1.exists()){
          succ = file1.delete();
      }
  }
  return succ;
}

Step 3

The function deletePermanent used implemented in the previous step returns a boolean value which will be used in this step. So if the deletePermanent method returns true indicating that the image has been deleted from the trashbin, first a method deleteFromRealm is invoked passing-in the path of the image in the Trashbin to delete the corresponding image’s record from the realm database. Thereafter, that particular trashbin item is removed from the ArrayList<TrashbinRealmModel> populating the TrashBin adapter to display the items in the TrashBin Activity and the adapter is notified of this change by the use of NotifyItemRemoved and NotifyItemRangeChanged methods of the RecyclerView adapter class passing-in the position of the item as parameter to the former and position along with the size of the updated list as parameters to the latter function. After the adapter is updated about the change in the dataset, the adapter re-populates the recyclerview thus displaying the remaining items in the trashbin section. The code snippets implementing the above-mentioned operations are provided below.

if(deletePermanent(trashBinRealmModel)){
  deleteFromRealm(trashItemsList.get(position).getTrashbinpath());
  trashItemsList.remove(position);
  notifyItemRemoved(position);
  notifyItemRangeChanged(position, trashItemsList.size());
}
private void deleteFromRealm(final String path){
  Realm realm = Realm.getDefaultInstance();
  realm.executeTransaction(new Realm.Transaction() {
      @Override public void execute(Realm realm) {
          RealmResults<TrashBinRealmModel> trashBinRealmModels = realm.where(TrashBinRealmModel.class).equalTo
                  (“trashbinpath”, path).findAll();
          trashBinRealmModels.deleteAllFromRealm();
      }
  });
}

This is how we have implemented the functionality to permanently delete an image from the Trashbin section in the Phimpme Android application. To get the full source code, please refer to the Phimpme Android Github repository listed in the resource section below.

Resources

  1. Android Developer documentation –https://developer.android.com/reference/java/io/File
  2. Github-Phimpme Android Repository – https://github.com/fossasia/phimpme-android/
  3. Realm database operations Android – https://www.androidhive.info/2016/05/android-working-with-realm-database-replacing-sqlite-core-data/
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