How to integrate RxJava into Android App with examples

In this tutorial, ozenero.com shows you way to integrate RxJava 2 into Android App, along with 3 simple examples that apply RxJava:

• CompoundButton (Switch) updates TextView
• Update TextView when text length in EditText changes
• Reactive Text search

Set up Android environment

We use Android Studio (installer from https://developer.android.com/studio/) for development. It doesn’t support RxJava, so we need to add RxJava 2 library.

Add RxJava 2 dependencies

Open app/build.gradle file, add RxJava and RxBinding wrappers for UI:

dependencies {
    ...

    implementation 'io.reactivex.rxjava2:rxjava:2.1.7'
    implementation 'io.reactivex.rxjava2:rxandroid:2.0.1'
    implementation 'com.jakewharton.rxbinding2:rxbinding:2.0.0'
}

Add Java 8 lambdas

We also need to add Java 8 to the configuration to use lambdas:

android {
    ...
    defaultConfig {
        ...
        compileOptions {
            sourceCompatibility JavaVersion.VERSION_1_8
            targetCompatibility JavaVersion.VERSION_1_8
        }
    }
    ...
}

Simple RxJava in Android App examples

Example 1: CompoundButton (Switch) updates TextView

Layout:

<Switch
    android:id="@+id/switch_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Press to Switch" />
<TextView
    android:id="@+id/text_view_1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

We’re gonna make Switch as an Observable.
– Create an Observable based on Switch (CompoundButton) change events using RxBindings library:

import com.jakewharton.rxbinding2.widget.RxCompoundButton;
import io.reactivex.Observable;
...

Switch switchButton = findViewById(R.id.switch_button);

Observable<Boolean> switchObservable = RxCompoundButton.checkedChanges(switchButton);

– Subscribe with listener function, it makes textView1 change text according to whether switchButton is checked or not.

TextView textView1 = findViewById(R.id.text_view_1);

switchObservable.subscribe(checked -> textView1.setText("Checked: " + checked));

Java code:

import com.jakewharton.rxbinding2.widget.RxCompoundButton;
...
public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ...
        Switch switchButton = findViewById(R.id.switch_button);
        TextView textView1 = findViewById(R.id.text_view_1);

        RxCompoundButton.checkedChanges(switchButton)
                .subscribe(checked -> textView1.setText("Checked: " + checked));
    }
}

Example 2: Update TextView when text length in EditText changes

Layout:

<EditText
    android:id="@+id/edit_text"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />
<TextView
    android:id="@+id/text_view_2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

We’re gonna make Text input as an Observable.
– Create an Observable based on EditText change events using RxBindings library:

import com.jakewharton.rxbinding2.widget.RxTextView;
import io.reactivex.Observable;

EditText editText = findViewById(R.id.edit_text);

Observable<CharSequence> edtTextObservable = RxTextView.textChanges(editText);

Now the EditText can be considered an emitter of string values over time.

– Subscribe with listener function, it makes textView2 say the text is “Too long!” if editText is more than 6 characters.

edtTextObservable.subscribe(text ->
                        textView2.setText(text.length() > 6 ? "Too long!" : ""));

Java code:

import com.jakewharton.rxbinding2.widget.RxTextView;
...
public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        EditText editText = findViewById(R.id.edit_text);
        TextView textView2 = findViewById(R.id.text_view_2);

        RxTextView.textChanges(editText)
                .subscribe(text ->
                        textView2.setText(text.length() > 6 ? "Too long!" : ""));
    }
}

Example 3: Reactive Text Search

Layout:

<EditText
    android:id="@+id/edit_text_search"
    android:layout_width="match_parent"
    android:layout_height="40dp"
    android:background="#fff"
    android:paddingLeft="10dp"
    android:paddingRight="10dp" />
<ListView
    android:id="@+id/search_results"
    android:layout_width="match_parent"
    android:layout_height="147dp"
    android:layout_marginTop="5dp"
    android:background="#fff" />

Searches fewer than 3 characters will be filtered out, and search request will be only sent once the user hasn’t typed for 500ms:

EditText editTextSearch = findViewById(R.id.edit_text_search);

RxTextView.textChanges(editTextSearch)
        .doOnNext(text -> this.clearSearchResults())
        .filter(text -> text.length() >= 3)
        .debounce(500, TimeUnit.MILLISECONDS)
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(this::updateSearchResults);

Notice that, debounce() operator will automatically switch the thread to a background. So we call .observeOn(AndroidSchedulers.mainThread()) before doing a UI operation (updateSearchResults()) in the next step.

Java code:

import com.jakewharton.rxbinding2.widget.RxTextView;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.TimeUnit;

import io.reactivex.android.schedulers.AndroidSchedulers;


public class MainActivity extends AppCompatActivity {
    ArrayAdapter arrayAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        arrayAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1);
        ListView listView = findViewById(R.id.search_results);
        listView.setAdapter(arrayAdapter);

        EditText editTextSearch = findViewById(R.id.edit_text_search);
        
        RxTextView.textChanges(editTextSearch)
                .doOnNext(text -> this.clearSearchResults())
                .filter(text -> text.length() >= 3)
                .debounce(500, TimeUnit.MILLISECONDS)
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(this::updateSearchResults);
    }

    private void clearSearchResults() {
        arrayAdapter.clear();
    }

    private void updateSearchResults(CharSequence text) {
        // Create some random results
        Random rand = new Random();
        List list = new ArrayList<>();
        for (int i = 0; i < 3; i++) {
            int n = rand.nextInt(100);
            list.add("" + text + "_" + n);
        }

        arrayAdapter.clear();
        arrayAdapter.addAll(list);
    }
}

Source Code

RxJava-Android-Intro