如何在Activity类中正确使用TextToSpeech？

import android.speech.tts.TextToSpeech;

private TextToSpeech textToSpeech;

textToSpeech = new TextToSpeech(this, new TextToSpeech.OnInitListener() {
    @Override
    public void onInit(int status) {
        if (status == TextToSpeech.SUCCESS) {
            // TextToSpeech初始化成功
        } else {
            // TextToSpeech初始化失败
        }
    }
});

int result = textToSpeech.setLanguage(Locale.US);
if (result == TextToSpeech.LANG_MISSING_DATA || result == TextToSpeech.LANG_NOT_SUPPORTED) {
    // 不支持所选语言
}

String text = "要播放的文本";
textToSpeech.speak(text, TextToSpeech.QUEUE_FLUSH, null);

if (textToSpeech != null) {
    textToSpeech.stop();
    textToSpeech.shutdown();
}