Android highlight a word in TextToSpeech

This post is about how to highlight the word while speech is running in TextToSpeech.

Creating new project

1. Create a new project by going to File ⇒ New Android Project, fill the required details and then click on finish.

2. The below layout file consist of two textView and a button to trigger a event that will highlight the word while speech is running in TextToSpeech.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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=".MainActivity">

    <TextView
        android:id="@+id/tv_text_to_speech"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="@dimen/margin_50dp"
        android:gravity="center"
        android:text="@string/text_to_speech"
        android:textColor="@color/colorPrimaryDark"
        android:textSize="@dimen/textSize_30sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tv_text"
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:layout_marginLeft="@dimen/margin_10dp"
        android:layout_marginRight="@dimen/margin_10dp"
        android:layout_marginTop="@dimen/margin_30dp"
        android:background="@drawable/background"
        android:textColor="@color/colorPrimaryDark"
        android:padding="@dimen/padding_8dp"
        app:layout_constraintEnd_toEndOf="parent"
        android:textSize="@dimen/textSize_25sp"
        app:layout_constraintStart_toStartOf="@+id/tv_text_to_speech"
        app:layout_constraintTop_toBottomOf="@+id/tv_text_to_speech" />
    
    <Button
        android:id="@+id/btn_speak_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="@dimen/margin_30dp"
        android:background="@color/colorPrimary"
        android:padding="@dimen/padding_12dp"
        android:onClick="startClicked"
        android:text="@string/speak_text"
        android:textColor="@android:color/white"
        android:textSize="@dimen/textSize_18sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="@+id/tv_text"
        app:layout_constraintStart_toStartOf="@+id/tv_text"
        app:layout_constraintTop_toBottomOf="@+id/tv_text" />

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.java

package com.c1ctech.highlighttextdemo;

import android.graphics.Color;
import android.os.Bundle;
import android.speech.tts.TextToSpeech;
import android.speech.tts.UtteranceProgressListener;
import android.text.Spannable;
import android.text.SpannableString;
import android.text.Spanned;
import android.text.style.ForegroundColorSpan;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements TextToSpeech.OnInitListener {
    TextToSpeech tts;

    String sentence = "The quick brown fox jumps over the lazy dog.";

    TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.tv_text);
        textView.setText(sentence);

        // creating TTS instance
        tts = new TextToSpeech(this, this);

    }

    public void onInit(int status) {

        tts.setOnUtteranceProgressListener(new UtteranceProgressListener() {

            @Override
            public void onStart(String utteranceId) {
                Log.i("TTS", "utterance started");
            }

            @Override
            public void onDone(String utteranceId) {
                Log.i("TTS", "utterance done");
            }

            @Override
            public void onError(String utteranceId) {
                Log.i("TTS", "utterance error");
            }

            @Override
            public void onRangeStart(String utteranceId,
                                     final int start,
                                     final int end,
                                     int frame) {
                Log.i("TTS", "onRangeStart() ... utteranceId: " + utteranceId + ", start: " + start
                        + ", end: " + end + ", frame: " + frame);


                // onRangeStart (and all UtteranceProgressListener callbacks) do not run on main thread
                // ... so we explicitly manipulate views on the main thread:
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {

                        Spannable textWithHighlights = new SpannableString(sentence);

                        textWithHighlights.setSpan(new ForegroundColorSpan(Color.RED), start, end, Spanned.SPAN_INCLUSIVE_INCLUSIVE);
                        textView.setText(textWithHighlights);

                    }
                });
            }
        });

    }

    public void startClicked(View ignored) {

        tts.speak(sentence, TextToSpeech.QUEUE_FLUSH, null, "UNIQUE_UTTERANCE_ID");

    }

    @Override
    public void onDestroy() {
        //don't forget to shutdown tts
        if (tts != null) {
            tts.stop();
            tts.shutdown();
        }
        super.onDestroy();
    }

}

Note: The setOnUtteranceProgressListener() method must be called before speak() is called.

In the above code,

• onInit(): Called to signal the completion of the TextToSpeech engine initialization.
• speak(): Speaks the text using the specified queuing strategy and speech parameters.
• onStart(): called when speaking starts (soon after calling speak()). 
• onDone(): called when speaking is finished.
• onError(): called when an error has occurred during processing.
• onRangeStart(): called when the TTS service is about to speak the specified range of the utterance with the given utteranceId.
• stop(): stop the speak.
• shutdown(): releases the resources used by the TextToSpeech engine.

4. Now run your project and test your app by clicking the button.