TwitterUsername

MVVM and RxJava sample that checks if a username is available on Twitter.

TwitterApi Network Request

Using an RxJava Adapter, we can make an Observable<TwitterResponse> to check for available usernames.

public interface TwitterApi {
    @GET("i/users/username_available.json")
    Observable<TwitterResponse> checkUsername(@Query("full_name") String fullName,
                                              @Query("suggest") boolean suggest,
                                              @Query("username") String userName);
}

ViewModel

Our ViewModel will house this network request so that it is idependent from configuration changes and other Activity/Fragment lifecycle events.

public class MainViewModel extends ViewModel {
    private TwitterService mTwitterService;

    MainViewModel(TwitterService twitterService){
        mTwitterService = twitterService;
    }

    Observable<TwitterResponse> checkUsername(String fullName, boolean suggest, String userName) {
        return mTwitterService.checkUsername(fullName, suggest, userName);
    }
}

Fragment and TextWatcher

Using a TextWatcher, we will observe changes made to the TextInputEditText on AndroidSchedulers.mainThread() to show either a success or error message.

    @Override
    public void onStart() {
        super.onStart();
        mUsernameEditText.addTextChangedListener(new TextWatcher() {
            ...

            @Override
            public void afterTextChanged(Editable s) {
                mCompositeDisposable.add(mViewModel.checkUsername("Droid", true, mUsernameEditText.getText().toString())
                        .debounce(300, TimeUnit.MILLISECONDS)
                        .distinctUntilChanged()
                        .subscribeOn(Schedulers.io())
                        .observeOn(AndroidSchedulers.mainThread())
                        .subscribe(new Consumer<TwitterResponse>() {
                            @Override
                            public void accept(TwitterResponse twitterResponse) throws Exception {
                                if (twitterResponse.valid) {
                                    showSuccessMessage();
                                } else {
                                    showErrorMessage();
                                }
                            }
                        }));
            }
        });
    }

Debounce

The debounce and distinctUntilChanged operators are used so that we avoid spamming the backend with a new network request everytime a character is entered. We will wait until 300ms after a character is entered before firing a checkUsername request.

.debounce(300, TimeUnit.MILLISECONDS)
.distinctUntilChanged()

Composite Disposables

In our Fragment's onStop(), we will clear all of our Rx subscriptions to prevent a memory leak using a CompositeDisposable. A CompositeDisposable allows us to keep track and clear multiple Rx subscriptions with a single call.

@Override
    public void onStop() {
        super.onStop();
        mCompositeDisposable.clear();
    }