IO

MyText = (TextView) findViewById(R.id.textView1);
// Добавить
void write() {
    try{
        // Читаем
        String line;
        // Открываем буфер
        BufferedWriter Writer = new BufferedWriter(new OutputStreamWriter(openFileOutput(FILENAME, MODE_PRIVATE), "UTF-8"));
        Writer.append(MyText.getText());
            Writer.flush();
            // Закрываем
        Writer.close();
        Log.d("WriterFile", "Записано!");
    } catch(FileNotFoundException e){
        e.printStackTrace();
    } catch(IOException e){
        e.printStackTrace();
    }
}