Create Call for Speakers with Open Event Organizer Android App

In The Open Event Organizer Android app, we were providing variety of features to the user but the functionality to create call for speakers for an Event was missing. This feature was required to attract speakers from all over the world to participate in the event and make it a success. Theis blog explains how we added this feature to the project us following MVVM Architecture and using libraries like Retrofit, RxJava, Db Flow etc.


The goal will be to provide an option to the organizer to create Call for Speakers for an Event (if it doesn’t exist already). We will provide the organizer a Floating Action Button in Speakers Call detail layout which will open a fragment which contain all the relevant fields provided by Open Event Server. The organizer can fill up all the fields as per requirement and create the call for speakers.


Let’s move on to the implementation details.

First, we will create the model which will contain all the fields offered by server. We are using Lombok library to reduce boilerplate code using annotations. For example, @Data annotation is used to generate getters and setters. @NoArgsConstructor to generate no arguments constructor as the name suggests. Along with that we are using @JonNaming annotation provided by Jackson library to serialize the model using KebabCaseStrategy. Also, the Table annotation provided by Raziz DbFlow library to make a table in database for this model.

@Table(database = OrgaDatabase.class, allFields = true)
public class SpeakersCall {@Id(LongIdHandler.class)
public Long id;@Relationship(“event”)
@ForeignKey(onDelete = ForeignKeyAction.CASCADE)
public Event event;

public String announcement;
public String hash;
public String privacy;
public String startsAt;
public String endsAt;

To handle this problem we will be using Retrofit 2.3.0 to make Network Requests, which is a REST client for Android and Java by Square Inc. It makes it relatively easy to retrieve and upload JSON (or other structured data) via a REST based Web Service. Also we will be using other awesome libraries like RxJava 2.1.10 (by ReactiveX) to handle tasks asynchronously, Jackson, Jasminb-Json-Api in an MVVM architecture.

We will make a POST request to the server . So we specify the declaration in

Observable<SpeakersCall> postSpeakersCall(@Body SpeakersCall speakersCall);

We will use the method createSpeakersCall(SpeakersCall speakersCall) in to interact with the SpeakersCallApi and make the network request for us. The response will be passed on to the SpeakersCallViewModel method which calls it.

public Observable<SpeakersCall> createSpeakersCall(SpeakersCall speakersCall) {
if (!repository.isConnected()) {
return Observable.error(new Throwable(Constants.NO_NETWORK));
}return speakersCallApi
.doOnNext(created -> {
.save(SpeakersCall.class, created)

Next, we will see the code for SpeakersCallViewModel which is using MVVM ViewModel to handle the processing logic for SpeakesCallFragment. Here we are passing SpeakersCallRepository instance in constructor. Methods like getProgress, getError and getSuccess pass on a LiveData Object from ViewModel to Fragment and the latter observes the changes on the object and show these in UI. CreateSpeakersCall method is used to call speakersCallRepository to send a POST request to server asynchronously using Retrofit and RxJava. Further, initialize method is used to set initial values of time and date to SpeakersCall object.

public class CreateSpeakersCallViewModel extends ViewModel {
public void createSpeakersCall(long eventId) {
if (!verify())
return;Event event = new Event();event.setId(eventId);

.doOnSubscribe(disposable -> progress.setValue(true))
.doFinally(() -> progress.setValue(false))
.subscribe(var -> success.setValue(“Speakers Call Created Successfully”),
throwable -> error.setValue(ErrorUtils.getMessage(throwable))));

We will create a Fragment class to bind the UI elements to the Model class so that they can be processed by ViewModel. The creation form contains less fields therefore BaseBottomSheetFragment is used. In the onStart method, we are binding several LiveData objects like SpeakersCall, Progress, Error, Success to the UI and then observe changes in them. Using LiveData we don’t have to write extra code to handle screen rotation and to update UI when the binded object is modified.

public class CreateSpeakersCallFragment extends BaseBottomSheetFragment implements CreateSpeakersCallView {
public void onStart() {
createSpeakersCallViewModel.getSpeakersCall().observe(this, this::showSpeakersCall);
createSpeakersCallViewModel.getProgress().observe(this, this::showProgress);
createSpeakersCallViewModel.getError().observe(this, this::showError);
createSpeakersCallViewModel.getSuccess().observe(this, this::onSuccess);

We will design the speaker create form using Two Way Data Binding to bind SpeakersCall object to the UI and use TextInputEditText to take user Input. Along with that we have used Time and Date pickers to make it easier to select Date and Time. For viewing the complete code, please refer here.

Thus, we are able to build a responsive, reactive UI using Android Architectural Components.


  1. Official documentation of Retrofit 2.x
  2. Official documentation for RxJava 2.x
  3. Official documentation for ViewModel
  4. Codebase for Open Event Orga App