Use RxJava to detect changes

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="lt.andro.learnrxjava.MainActivity"
    >

    <TextView
        android:id="@+id/main_output"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        />

    <EditText
        android:id="@+id/main_input1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@id/main_output"
        tools:text="Name"
        />

    <EditText
        android:id="@+id/main_input2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@id/main_input1"
        tools:text="Name"
        />

    <EditText
        android:id="@+id/main_input3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@id/main_input2"
        tools:text="Name"
        />

    <EditText
        android:id="@+id/main_input4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@id/main_input3"
        tools:text="Name"
        />

    <RadioGroup
        android:id="@+id/main_radio_group"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="16dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@id/main_input4"
        >

        <RadioButton
            android:id="@+id/main_radio1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Radio1"
            />

        <RadioButton
            android:id="@+id/main_radio2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Radio2"
            />

        <RadioButton
            android:id="@+id/main_radio3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Radio3"
            />

        <RadioButton
            android:id="@+id/main_radio4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Radio4"
            />
    </RadioGroup>

</android.support.constraint.ConstraintLayout>

build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 26
    buildToolsVersion "26.0.1"
    defaultConfig {
        applicationId "lt.andro.learnrxjava"
        minSdkVersion 15
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:26.0.0-alpha1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    testCompile 'junit:junit:4.12'

    compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
    compile 'io.reactivex.rxjava2:rxjava:2.1.2'
    compile 'com.jakewharton.rxbinding2:rxbinding:2.0.0'
    compile 'com.jakewharton.rxbinding2:rxbinding-support-v4:2.0.0'
    compile 'com.jakewharton.rxbinding2:rxbinding-appcompat-v7:2.0.0'
    compile 'com.jakewharton.rxbinding2:rxbinding-design:2.0.0'
    compile 'com.jakewharton.rxbinding2:rxbinding-recyclerview-v7:2.0.0'


}

MainActivity.java

package lt.andro.learnrxjava;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.Editable;
import android.text.TextUtils;
import android.widget.RadioGroup;
import android.widget.TextView;

import com.jakewharton.rxbinding2.InitialValueObservable;
import com.jakewharton.rxbinding2.widget.RxRadioGroup;
import com.jakewharton.rxbinding2.widget.RxTextView;
import com.jakewharton.rxbinding2.widget.TextViewAfterTextChangeEvent;

import java.util.Arrays;
import java.util.List;

import io.reactivex.Flowable;
import io.reactivex.Observable;
import io.reactivex.annotations.NonNull;
import io.reactivex.functions.Consumer;
import io.reactivex.functions.Function;
import io.reactivex.functions.Function4;

public class MainActivity extends AppCompatActivity {

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

        TextView outputView = (TextView) findViewById(R.id.main_output);
        TextView input1View = (TextView) findViewById(R.id.main_input1);
        TextView input2View = (TextView) findViewById(R.id.main_input2);
        TextView input3View = (TextView) findViewById(R.id.main_input3);
        TextView input4View = (TextView) findViewById(R.id.main_input4);
        RadioGroup inputRG = (RadioGroup) findViewById(R.id.main_radio_group);

        outputView.setText("output");
        input1View.setText("input1");
        input2View.setText("input2");
        input3View.setText("input3");
        input4View.setText("input4");
        inputRG.check(R.id.main_radio2);


        Consumer<? super CharSequence> output = RxTextView.text(outputView);
        InitialValueObservable<TextViewAfterTextChangeEvent> rxInput1 = RxTextView.afterTextChangeEvents(input1View);
        InitialValueObservable<TextViewAfterTextChangeEvent> rxInput2 = RxTextView.afterTextChangeEvents(input2View);
        InitialValueObservable<TextViewAfterTextChangeEvent> rxInput3 = RxTextView.afterTextChangeEvents(input3View);
        InitialValueObservable<TextViewAfterTextChangeEvent> rxInput4 = RxTextView.afterTextChangeEvents(input4View);
        InitialValueObservable<Integer> rxInputRG = RxRadioGroup.checkedChanges(inputRG);

        Observable<String> input1 = getInputAsStrings(rxInput1);
        Observable<String> input2 = getInputAsStrings(rxInput2);
        Observable<String> input3 = getInputAsStrings(rxInput3);
        Observable<String> input4 = getInputAsStrings(rxInput4);


//        combineV1(output, input1, input2, input3, input4);
        combineV2(output, rxInputRG, input1, input2, input3, input4);
    }

    private void combineV2(Consumer<? super CharSequence> output, InitialValueObservable<Integer> rxInputRG, Observable<String> input1, Observable<String> input2, Observable<String> input3, Observable<String> input4) {
        Function<Object[], Object> combiner = new Function<Object[], Object>() {
            List<Object> initial;

            @Override
            public Object apply(@NonNull Object[] objects) throws Exception {
                List<Object> combined = Arrays.asList(objects);
                if (initial == null) {
                    initial = combined;
                }
                return initial.equals(combined);
            }
        };
        Observable
                .combineLatest(combiner, Flowable.bufferSize(), input1, input2, input3, input4, rxInputRG)
                .map(new Function<Object, String>() {
                    @Override
                    public String apply(@NonNull Object o) throws Exception {
                        return o.toString();
                    }
                })
                .doOnNext(output)
                .subscribe();
    }

    private void combineV1(Consumer<? super CharSequence> output, Observable<String> input1, Observable<String> input2, Observable<String> input3, Observable<String> input4) {
        Function4<String, String, String, String, Boolean> checkForChanges = new Function4<String, String, String, String, Boolean>() {
            String initialValue = "";

            @Override
            public Boolean apply(@NonNull String s1, @NonNull String s2, @NonNull String s3, @NonNull String s4) throws Exception {
                String combined = s1 + ":" + s2 + ":" + s3 + ":" + s4;
                if (TextUtils.isEmpty(initialValue)) initialValue = combined;
                return initialValue.equals(combined);
            }
        };
        Observable
                .combineLatest(input1, input2, input3, input4, checkForChanges)
                .map(new Function<Boolean, String>() {
                    @Override
                    public String apply(@NonNull Boolean aBoolean) throws Exception {
                        return aBoolean.toString();
                    }
                })
                .doOnNext(output)
                .subscribe();
    }

    private Observable<String> getInputAsStrings(Observable<TextViewAfterTextChangeEvent> inputs) {
        Function<TextViewAfterTextChangeEvent, String> toString = new Function<TextViewAfterTextChangeEvent, String>() {
            @Override
            public String apply(@NonNull TextViewAfterTextChangeEvent changeEvent) throws Exception {
                Editable editable = changeEvent.editable();
                if (editable != null) {
                    return editable.toString();
                } else {
                    return "";
                }
            }
        };
        return inputs.map(toString);
    }
}