How get *.txt from assets subfolder

Question

I'm a beginner and I would like to ask why is this code not working?

I'm trying to achieve how to open *.txt files at option in assets subdirectory.

mTopicOneList = new ArrayList(Arrays.asList(getResources().getStringArray(R.array.topic_one)));

ListView list = (ListView) findViewById(R.id.topic_one_list);
list.setOnItemClickListener(new OnItemClickListener() {

        @Override
        public void onItemClick(AdapterView<?> adapter, View view,
                                int position, long id) {
            intent = new Intent(view.getContext(), TextActivity.class);
            AssetManager assetManager = getApplicationContext().getAssets();
            InputStream input;
            String assetsString;

            try {

                String[] subDirectoryFileList = assetManager.list("topicone/");
                input = assetManager.open(subDirectoryFileList[position]);

                int size = input.available();
                byte[] buffer = new byte[size];
                input.read(buffer);
                input.close();

                assetsString = new String(buffer);
                intent.putExtra("textFromAssets",assetsString);

            } catch (IOException e) {
                e.printStackTrace();
            }
            startActivity(intent);
        }

});