You can save your textview data to a text file by this code example:
File root = new File(YOUR_DIRECTORY_PATH);
File gpxfile = new File(root, "yourFileName.txt");
FileWriter writer = new FileWriter(gpxfile);
writer.append(yourTextview.getText().toString());
writer.flush();
writer.close();
To send the file as email attachment you can try:
Intent sendIntent = new Intent();
sendIntent.setAction(Intent.ACTION_SEND);
sendIntent.putExtra(Intent.EXTRA_STREAM, Uri.fromFile(YOUR_FILE_PATH));
sendIntent.setType("text/plain");
startActivity(sendIntent);
You can make 2 separate methods for these 2 tasks and use them in your button click event, that's all.