Question

The TextToSpeech constructor looks like it’s designed to be ‘owned’ by an Activity. I’m producing an app with multiple different Activities, and I don’t want to have to initialise a new TextToSpeech instance for each – I want the speech to carry on smoothly even if the Activity is changing.

My idea is to have a static TextToSpeech object accessed by all activities, initialised by the first one.

1. Does anyone know if the TextToSpeech implementation is thread-safe? I’m guessing not, but someone out there might know.
2. If I initialise it with the Context of my default Activity, will the TextToSpeech instance stop working when the Activity is destroyed?

Answer 1

Thanks to those that told me to pass the ApplicationContext. Turned out that was the easy bit… The hard bit was whether the TextToSpeech object is guaranteed thread-safe.

Thanks for answers telling me how to make something thread-safe / assuming that it is, but the question was about whether the object already is. I probably should have said, I’m fine with implementing thread-safety, but I wanted to know whether I need to bother. And I don’t want to assume thread-safety without being certain.

I ran the following and it seemed to work. So I assume the Android SDK TTS is thread-safe, but can’t find any documentation saying that it’s safe to assume this across all devices, so I’ll be wrapping my TTS instance for the time being!

package com.example.testproject;

import java.util.Random;

import android.os.Bundle;
import android.app.Activity;
import android.speech.tts.TextToSpeech;
import android.speech.tts.TextToSpeech.OnInitListener;

public class TestActivity extends Activity implements OnInitListener {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        tts = new TextToSpeech(getApplicationContext(), this);
    }

    TextToSpeech tts = null;

    @Override
    public void onInit(int arg0) {
        for (int i = 0; i < 100; ++i) {
            class Irritate implements Runnable {
                Irritate(int iIn) {
                    i = iIn;
                }

                @Override
                public void run() {
                    Random r = new Random();
                    try {
                        Thread.sleep(r.nextInt(2000));
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                    tts.speak(Integer.toString(i), TextToSpeech.QUEUE_ADD, null);
                }

                int i;
            }

            Thread t = new Thread(new Irritate(i));

            t.start();
        }
    }
}