NFC Android 多次读取 NDEF 标签

Question

我有一个可以读取 NDEF 标签的应用，没什么大不了的 :-)

我想多次读取一个 NDEF 标签，显然是要相应地更新标签。想象一下，我的 NDEF 标记将包含时间 (hh:mm:ss)，当我用我的应用程序读取它时，我想在手机上看到时间的变化。 如果我将手机放在标签上打开和关闭的位置，这有点工作，但我希望能够自动检测 NDEF 标签，只要它在那里，我想每 x 秒读取一次它的内容。

我找到了这个链接： Write NDEF message multiple times to same tag? 但它是关于写几次，我想读。

我找到了这个链接： How to find out whether an NFC tag is still in range of an Android now? 什么是开始，但我不知道如何更新标签。

我很挣扎，我什至不知道我尝试做的事情在技术上是否可行。

有没有人有一些关于如何做到这一点的提示？ 干杯

更多信息

这是我的 onCreate

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

        /// trying something
        ScheduledExecutorService exec = Executors.newSingleThreadScheduledExecutor();
        exec.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                // do stuff
                Log.d(TAG, "i am printing ");
            }
        }, 0, 5, TimeUnit.SECONDS);

        new Thread(new Runnable() {
            @Override
            public void run() {
                // here ask for TAG
                // read the TAG
                // and update the clock
            }
        }).start(); // Start the operation

        /////////////////

        mTextView = (TextView) findViewById(R.id.textView_explanation);

        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

        if (mNfcAdapter == null) {

            // Stop here, we definitely need NFC
            Toast.makeText(this, "This device doesn't support NFC.",
                    Toast.LENGTH_LONG).show();
            finish();
            return;
        }

        if (!mNfcAdapter.isEnabled()) {
            mTextView.setText("NFC is currently disabled on this device.");
        }

        handleIntent(getIntent());
    }

还有我的handleIntent：

private void handleIntent(Intent intent) {
        String action = intent.getAction();
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {

            String type = intent.getType();
            if (MIME_TEXT_PLAIN.equals(type)) {

                Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
                new NdefReaderTask().execute(tag);

            } else {
                Log.d(TAG, "Wrong mime type: " + type);
            }
        } else if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {

            // In case we would still use the Tech Discovered Intent
            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            String[] techList = tag.getTechList();
            String searchedTech = Ndef.class.getName();

            for (String tech : techList) {
                if (searchedTech.equals(tech)) {
                    new NdefReaderTask().execute(tag);
                    break;
                }
            }
        }
    }

在 ScheduledExecutorService 中，我添加了“Log.d(TAG,”我正在打印“);”，只是为了尝试理解它确实可以正常工作并定期打印。我没有得到的是，如果我要求 TAG，读取 TAG 并更新新线程中的时钟，我应该在 ScheduledExecutorService 中做什么，以及如何要求 TAG，读取 TAG 并更新新线程内的时钟，当它当前在 onCreate 方法之外完成时？例如，读取的结果发布在我的 onPostExecute 方法中的 textView 中。

抱歉，我已经尝试观看一些教程和示例，但我仍然不明白。

更多信息 2

这是我的全部代码。读取标签需要更长的时间，有时不需要。我不知道如何以及在哪里更新标签，以防出现问题。完全迷路了:-(

package uk.co.xxx.xxx;

import android.nfc.FormatException;
import android.support.v7.app.AppCompatActivity;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.Arrays;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.IntentFilter.MalformedMimeTypeException;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.Ndef;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {

    public static final String MIME_TEXT_PLAIN = "text/plain";
    public static final String TAG = "NfcDemo";

    private TextView mTextView;
    private NfcAdapter mNfcAdapter;

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

        /// trying something
        ScheduledExecutorService exec = Executors.newSingleThreadScheduledExecutor();
        exec.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                // do stuff
                handleIntent(getIntent());
                Log.d(TAG, "i am printing ");
            }
        }, 0, 5, TimeUnit.SECONDS);
        /////////////////

        mTextView = (TextView) findViewById(R.id.textView_explanation);

        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

        if (mNfcAdapter == null) {

            Toast.makeText(this, "This device doesn't support NFC.",
                    Toast.LENGTH_LONG).show();
            finish();
            return;
        }

        if (!mNfcAdapter.isEnabled()) {
            mTextView.setText("NFC is currently disabled on this device.");
        }

        handleIntent(getIntent());
    }



    @Override
    protected void onResume() {
        super.onResume();

        /**
         * It's important, that the activity is in the foreground (resumed). Otherwise
         * an IllegalStateException is thrown.
         */
        setupForegroundDispatch(this, mNfcAdapter);
    }

    @Override
    protected void onPause() {
        /**
         * Call this before onPause, otherwise an IllegalArgumentException is thrown as well.
         */
        stopForegroundDispatch(this, mNfcAdapter);

        super.onPause();
    }

    @Override
    protected void onNewIntent(Intent intent) {
        /**
         * This method gets called, when a new Intent gets associated with the current activity instance.
         * Instead of creating a new activity, onNewIntent will be called. For more information have a look
         * at the documentation.
         *
         * In our case this method gets called, when the user attaches a Tag to the device.
         */
        handleIntent(intent);
    }


    private void handleIntent(Intent intent) {
        String action = intent.getAction();
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {

            String type = intent.getType();
            if (MIME_TEXT_PLAIN.equals(type)) {

                Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
                new NdefReaderTask().execute(tag);


            } else {
                Log.d(TAG, "Wrong mime type: " + type);
            }
        } else if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {

            // In case we would still use the Tech Discovered Intent
            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            String[] techList = tag.getTechList();
            String searchedTech = Ndef.class.getName();

            for (String tech : techList) {
                if (searchedTech.equals(tech)) {
                    new NdefReaderTask().execute(tag);
                    break;
                }
            }
        }
    }


    public static void setupForegroundDispatch(final Activity activity, NfcAdapter adapter) {
        final Intent intent = new Intent(activity.getApplicationContext(), activity.getClass());
        intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);

        final PendingIntent pendingIntent = PendingIntent.getActivity(activity.getApplicationContext(), 0, intent, 0);

        IntentFilter[] filters = new IntentFilter[1];
        String[][] techList = new String[][]{};


        filters[0] = new IntentFilter();
        filters[0].addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
        filters[0].addCategory(Intent.CATEGORY_DEFAULT);
        try {
            filters[0].addDataType(MIME_TEXT_PLAIN);
        } catch (MalformedMimeTypeException e) {
            throw new RuntimeException("Check your mime type.");
        }

        adapter.enableForegroundDispatch(activity, pendingIntent, filters, techList);
    }


    public static void stopForegroundDispatch(final Activity activity, NfcAdapter adapter) {
        adapter.disableForegroundDispatch(activity);
    }

    /**
     * Background task for reading the data. Do not block the UI thread while reading.
     */

    private class NdefReaderTask extends AsyncTask<Tag, Void, String> {

        @Override
        protected String doInBackground(Tag... params) {
            Tag tag = params[0];

            Ndef ndef = Ndef.get(tag);
            if (ndef == null) {
                // NDEF is not supported by this Tag.
                return null;
            }

            NdefMessage ndefMessage = ndef.getCachedNdefMessage();

            NdefRecord[] records = ndefMessage.getRecords();
            for (NdefRecord ndefRecord : records) {
                if (ndefRecord.getTnf() == NdefRecord.TNF_WELL_KNOWN && Arrays.equals(ndefRecord.getType(), NdefRecord.RTD_TEXT)) {
                    try {
                        return readText(ndefRecord);
                    } catch (UnsupportedEncodingException e) {
                        Log.e(TAG, "Unsupported Encoding", e);
                    }
                }
            }

            return null;
        }

        private String readText(NdefRecord record) throws UnsupportedEncodingException {

            byte[] payload = record.getPayload();

            // Get the Text Encoding

            String textEncoding = new String ("");
            if ((payload[0] & 128) == 0) {
                textEncoding = "UTF-8";
            } else {
                textEncoding = "UTF-16";
            }

            // Get the Language Code
            int languageCodeLength = payload[0] & 63;


            // Get the Text
            return new String(payload, languageCodeLength + 1, payload.length - languageCodeLength - 1, textEncoding);
        }

        @Override
        protected void onPostExecute(String result) {
            if (result != null) {
                mTextView.setText("The time is: \n" + result);
            }
        }
    }
}

Answer 1

使用TAG = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);，您可以获得标签。现在，您可以每 x 秒检查一次 TAG，如果它不为空（或者它具有最后检测到的类型），您可以读取标签并更新时钟（我想它是一个文本视图）。 您可以在 Thread 中执行此操作，例如：

new Thread(new Runnable() {
  @Override
  public void run() {
  // here ask for TAG
  // read the TAG
  // and update the clock             
  }
}).start(); // Start the operation

我希望我正确理解了您的问题。