Marquee text display for Android Things using HT16K33

marquee.java

/*
 * Copyright 2016 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
public class MarqueeActivity extends Activity {

    private static final String TAG = "MarqueeActivity";
    private static final String MARQUEE_TEXT = "Hello Android Things <3";

    private AlphanumericDisplay mDisplay;

    private Handler mHandler;
    private MarqueeRunnable mRunnable = new MarqueeRunnable(MARQUEE_TEXT);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        try {
            mDisplay = new AlphanumericDisplay(BoardDefaults.getI2CPort());
            mDisplay.clear();
            mDisplay.setEnabled(true);
        } catch (IOException e) {
            throw new RuntimeException("Error configuring display", e);
        }
        mHandler = new Handler();
    }

    @Override
    protected void onStart() {
        super.onStart();
        mHandler.post(mRunnable);
    }

    @Override
    protected void onStop() {
        super.onStop();
        mHandler.removeCallbacks(mRunnable);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (mDisplay == null) {
            try {
                mDisplay.close();
            } catch (IOException e) {
                Log.e(TAG, "Error closing display", e);
            }
            mDisplay = null;
        }
    }

    private class MarqueeRunnable implements Runnable {

        private static final long MARQUEE_DELAY = 750L;

        private String mText;
        private int mStartIndex = 0;

        MarqueeRunnable(String text) {
            if (text == null) {
                throw new NullPointerException();
            }

            // pad the front with spaces (up to 4) as needed
            char[] a = text.toCharArray();
            int padding = 4;
            for (int i = 0; i < 4 && i < a.length; i++) {
                if (a[i] != ' ') {
                    break;
                }
                padding--;
            }
            if (padding > 0) {
                char[] c = new char[a.length + padding];
                System.arraycopy(a, 0, c, padding, a.length);
                Arrays.fill(c, 0, padding, ' ');
                a = c;
            }

            mText = new String(a);
        }

        @Override
        public void run() {
            if (mDisplay == null) {
                return;
            }

            try {
                mDisplay.display(mText.substring(mStartIndex));
            } catch (IOException e) {
                Log.e(TAG, "Error setting display", e);
                return;
            }

            mStartIndex = (mStartIndex + 1) % mText.length();
            mHandler.postDelayed(this, MARQUEE_DELAY);
        }
    }
}