NFCReader.java

package at.renehollander.schnitzeljagd.sensor;

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * 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.
 */

import android.annotation.TargetApi;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.Ndef;
import android.os.Build;
import android.util.Log;

import java.io.UnsupportedEncodingException;
import java.lang.ref.WeakReference;

/**
 * Callback class, invoked when an NFC card is scanned while the device is running in reader mode.
 * <p>
 * Reader mode can be invoked by calling NfcAdapter
 */
@TargetApi(Build.VERSION_CODES.KITKAT)
public class NFCReader implements NfcAdapter.ReaderCallback {
    private static final String TAG = "NFCReader";

    // Weak reference to prevent retain loop. mAccountCallback is responsible for exiting
    // foreground mode before it becomes invalid (e.g. during onPause() or onStop()).
    private WeakReference<AccountCallback> mAccountCallback;

    public interface AccountCallback {
        void onAccountReceived(String account);
    }

    public NFCReader(AccountCallback accountCallback) {
        mAccountCallback = new WeakReference<AccountCallback>(accountCallback);
    }

    /**
     * Callback when a new tag is discovered by the system.
     * <p>
     * <p>Communication with the card should take place here.
     *
     * @param tag Discovered tag
     */
    @Override
    public void onTagDiscovered(Tag tag) {
        Log.i(TAG, "New tag discovered");
        this.readTextFromTag(tag);
    }

    private void readTextFromTag(Tag tag) {
        Ndef ndefTag = Ndef.get(tag);
        NdefMessage ndefMessage = ndefTag.getCachedNdefMessage();
        NdefRecord[] ndefRecords = ndefMessage.getRecords();
        if (ndefRecords != null && ndefRecords.length > 0) {
            NdefRecord ndefRecord = ndefRecords[0];
            String tagContent = getTextFromNdefRecord(ndefRecord);
            Log.i(TAG, "Received: " + tagContent);
            mAccountCallback.get().onAccountReceived(tagContent);
        } else {
            Log.i(TAG, "No NDEF records found");
        }
    }

    private static String getTextFromNdefRecord(NdefRecord ndefRecord) {
        String tagContent = null;
        try {
            byte[] payload = ndefRecord.getPayload();
            String textEncoding = ((payload[0] & 128) == 0) ? "UTF-8" : "UTF-16";
            int languageSize = payload[0] & 0063;
            tagContent = new String(payload, languageSize + 1, payload.length - languageSize - 1, textEncoding);
        } catch (UnsupportedEncodingException e) {
            Log.e("getTextFromNdefRecord", e.getMessage(), e);
        }
        return tagContent;
    }
}