Playing with Android TextWatcher

TextWatcherActivity.java

package org.coursera.four;

import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.Display;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.TextView;

public class TextWatcherActivity extends ActionBarActivity {

    TextView reverseTextView;
    Display metrics;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_text_watcher);

        // Old up navigation for activity.
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        // Get EditText and add TextWatcher.
        EditText editText = (EditText) findViewById(R.id.edit_text_watcher);
        editText.addTextChangedListener(watcher);

        // Get TextView for reversed text.
        reverseTextView = (TextView) findViewById(R.id.inverse_text);
    }

    TextWatcher watcher = new TextWatcher() {
        @Override
        public void afterTextChanged(Editable arg0) {
            // Nothing to see here.
        }

        @Override
        public void beforeTextChanged(CharSequence arg0, int arg1, int arg2, int arg3) {
            // Move along.
        }

        @Override
        public void onTextChanged(CharSequence s, int a, int b, int c) {
            // Get display metrics.
            metrics = getWindowManager().getDefaultDisplay();

            // Get watcher text as String.
            String text = s.toString();

            // Reverse text and add to TextView.
            String inversedText = new StringBuilder(s).reverse().toString();
            reverseTextView.setText(inversedText);

            // Create a canvas with same width as screen.
            // TODO: It may not be a good idea to create the complete canvas each time.
            Bitmap bitmap = Bitmap.createBitmap(metrics.getWidth(), 200, Bitmap.Config.ARGB_8888);
            Canvas canvas = new Canvas(bitmap);

            // Paint some cyan text on the canvas.
            Paint paint = new Paint();
            canvas.drawPaint(paint);
            paint.setColor(Color.CYAN);
            paint.setTextSize(28);
            canvas.drawText(text, 10, 25, paint);

            // Add the canvas to the ImageView.
            ImageView canvasImageView = (ImageView) findViewById(R.id.canvas_image_view);
            canvasImageView.setImageBitmap(bitmap);
        }
    };
}