How to use TTS in offline mode ?

[youcef23b]

I found this code in the Demo app, but it work only on online mode, I want to use the TTS features in offline mode.

(findViewById(R.id.btn_start_tts)).setOnClickListener(new View.OnClickListener() {
TTSRequest ttsRequest = new TTSRequest("语音合成测试：北京海淀区天气晴朗，气温20度到26度");

        public void onClick(View v) {

            SpeechClient.getInstance().startTTS(ttsRequest, new TTSListener() {
                @Override
                public void onStart() {
                    Log.i(TAG, "onStart");
                }

                @Override
                public void onError(int errorCode) {
                    Log.i(TAG, "onError " + errorCode);
                }

                @Override
                public void onDone() {
                    Log.i(TAG, "onDone");
                }
            });
        }
    });