空NFC标签读写Android应用程序。扫描空标签时手机自己的消息返回，但应用程序不工作？

Question

我已经制作了一个在NFC TAG上读写的应用程序。但是，当我在打开应用程序后扫描空 NFC 标签时，它没有像我预期的那样响应，因为我的应用程序吐司消息“标签为空”。但是，当我关闭我的应用程序时，我会收到移动传送带消息。

基本上，我需要如下帮助:

1. 从我的应用程序中检测空NFC标签
2. 在该空标记中写入服务器信息
3. 然后从该标签中读取该信息

我在这里包含了我的代码。

Android清单.xml

    <?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.mylab.myapplication">

    <uses-permission android:name="android.permission.NFC" />
    <uses-feature android:name="android.hardware.nfc" android:required="true" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.MyApplication">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

            <intent-filter>
                <action android:name="android.nfc.action.NDEF_DISCOVERED" />
                <category android:name="android.intent.category.DEFAULT" />
                <data android:mimeType="text/plain" />
            </intent-filter>
            <meta-data
                android:name="android.nfc.action.TECH_DISCOVERED"
                android:resource="@xml/nfc_tech_filter" />
        </activity>
    </application>

</manifest>

activity_main.xml

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Write a message: ">
    </TextView>

    <LinearLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20sp" >

        <EditText
            android:id="@+id/edit_message"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="2"
            android:hint="message" />
        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Write" />
    </LinearLayout>
    <TextView
        android:id="@+id/nfc_contents"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        />
</LinearLayout>

nfc_tech_filter.xml

    <?xml version="1.0" encoding="utf-8"?>
<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
    <tech-list>
        <tech>android.nfc.tech.Ndef</tech>
        <!-- class name -->
    </tech-list>
</resources>

MainActivity.java

    public class MainActivity extends AppCompatActivity {

    public static final String ERROR_DETECTED = "No NFC tag detected!";
    public static final String WRITE_SUCCESS = "Text written to the NFC tag successfully!";
    public static final String WRITE_ERROR = "Error during writing, is the NFC tag close enough to your device?";
    NfcAdapter nfcAdapter;
    PendingIntent pendingIntent;
    IntentFilter writeTagFilters[];
    boolean writeMode;
    Tag myTag;
    Context context;

    TextView tvNFCContent;
    TextView message;
    Button btnWrite;

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

        tvNFCContent = (TextView) findViewById(R.id.nfc_contents);
        message = (TextView) findViewById(R.id.edit_message);
        btnWrite = (Button) findViewById(R.id.button);

        btnWrite.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v) {
                try {
                    if(myTag ==null) {
                        Toast.makeText(context, ERROR_DETECTED, Toast.LENGTH_LONG).show();
                    } else {
                        write(message.getText().toString(), myTag);
                        Toast.makeText(context, WRITE_SUCCESS, Toast.LENGTH_LONG ).show();
                    }
                } catch (IOException e) {
                    Toast.makeText(context, WRITE_ERROR, Toast.LENGTH_LONG ).show();
                    e.printStackTrace();
                } catch (FormatException e) {
                    Toast.makeText(context, WRITE_ERROR, Toast.LENGTH_LONG ).show();
                    e.printStackTrace();
                }
            }
        });

        nfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if (nfcAdapter == null) {
            // Stop here, we definitely need NFC
            Toast.makeText(this, "This device doesn't support NFC.", Toast.LENGTH_LONG).show();
            finish();
        }
        readFromIntent(getIntent());

        pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
        IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
        tagDetected.addCategory(Intent.CATEGORY_DEFAULT);
        writeTagFilters = new IntentFilter[] { tagDetected };
    }

    /******************************************************************************
     **********************************Read From NFC Tag***************************
     ******************************************************************************/
    private void readFromIntent(Intent intent) {
        String action = intent.getAction();
        if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action)
                || NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)
                || NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
            Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
            NdefMessage[] msgs = null;
            if (rawMsgs != null) {
                msgs = new NdefMessage[rawMsgs.length];
                for (int i = 0; i < rawMsgs.length; i++) {
                    msgs[i] = (NdefMessage) rawMsgs[i];
                }
            }
            buildTagViews(msgs);
        }
    }
    private void buildTagViews(NdefMessage[] msgs) {
        if (msgs == null || msgs.length == 0) return;

        String text = "";
//        String tagId = new String(msgs[0].getRecords()[0].getType());
        byte[] payload = msgs[0].getRecords()[0].getPayload();
        String textEncoding = ((payload[0] & 128) == 0) ? "UTF-8" : "UTF-16"; // Get the Text Encoding
        int languageCodeLength = payload[0] & 0063; // Get the Language Code, e.g. "en"
        // String languageCode = new String(payload, 1, languageCodeLength, "US-ASCII");

        try {
            // Get the Text
            text = new String(payload, languageCodeLength + 1, payload.length - languageCodeLength - 1, textEncoding);
        } catch (UnsupportedEncodingException e) {
            Log.e("UnsupportedEncoding", e.toString());
        }

        tvNFCContent.setText("NFC Content: " + text);
    }

    /******************************************************************************
     **********************************Write to NFC Tag****************************
     ******************************************************************************/
    private void write(String text, Tag tag) throws IOException, FormatException {
        NdefRecord[] records = { createRecord(text) };
        NdefMessage message = new NdefMessage(records);
        // Get an instance of Ndef for the tag.
        Ndef ndef = Ndef.get(tag);
        // Enable I/O
        ndef.connect();
        // Write the message
        ndef.writeNdefMessage(message);
        // Close the connection
        ndef.close();
    }
    private NdefRecord createRecord(String text) throws UnsupportedEncodingException {
        String lang       = "en";
        byte[] textBytes  = text.getBytes();
        byte[] langBytes  = lang.getBytes("US-ASCII");
        int    langLength = langBytes.length;
        int    textLength = textBytes.length;
        byte[] payload    = new byte[1 + langLength + textLength];

        // set status byte (see NDEF spec for actual bits)
        payload[0] = (byte) langLength;

        // copy langbytes and textbytes into payload
        System.arraycopy(langBytes, 0, payload, 1,              langLength);
        System.arraycopy(textBytes, 0, payload, 1 + langLength, textLength);

        NdefRecord recordNFC = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,  NdefRecord.RTD_TEXT,  new byte[0], payload);

        return recordNFC;
    }

    @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
        setIntent(intent);
        readFromIntent(intent);
        if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())) {
            myTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
        }
    }

    @Override
    public void onPause(){
        super.onPause();
        WriteModeOff();
    }

    @Override
    public void onResume(){
        super.onResume();
        WriteModeOn();
    }

    /******************************************************************************
     **********************************Enable Write********************************
     ******************************************************************************/
    private void WriteModeOn(){
        writeMode = true;
        nfcAdapter.enableForegroundDispatch(this, pendingIntent, writeTagFilters, null);
    }
    /******************************************************************************
     **********************************Disable Write*******************************
     ******************************************************************************/
    private void WriteModeOff(){
        writeMode = false;
        nfcAdapter.disableForegroundDispatch(this);
    }
}

Answer 1

要处理未格式化的Ndef标签，请将您的“nfc_tech_filter.xml”文件更改为以下文件：-

<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
    <tech-list>
        <tech>android.nfc.tech.Ndef</tech>
        <tech>android.nfc.tech.NdefFormatable</tech>
    </tech-list>
</resources>

这样，您的应用程序说它希望在检测到NdeFormatable标签时得到通知，这将阻止您在呈现这些标签之一时看到Android操作系统显示它自己的消息。（如果呈现了一个永远无法存储Ndef消息的标签，操作系统仍然会显示一条消息）

然后重构处理系统传递给应用程序的意图，以处理传递的标记

private void readFromIntent(Intent intent) {
        String action = intent.getAction();
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {
            Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
            NdefMessage[] msgs = null;
            msgs = new NdefMessage[rawMsgs.length];
            for (int i = 0; i < rawMsgs.length; i++) {
                 msgs[i] = (NdefMessage) rawMsgs[i];
            }
            buildTagViews(msgs);
        }
    }

private void write(String text, Tag tag) throws IOException, FormatException {
        NdefRecord[] records = { createRecord(text) };
        NdefMessage message = new NdefMessage(records);
        // Get an instance of Ndef for the tag.
        Ndef ndef = Ndef.get(tag);
        // If Ndef.get is null then try formatting it and adding message
        if (ndef != null) {
          // Enable I/O
          ndef.connect();
          // Write the message
          ndef.writeNdefMessage(message);
          // Close the connection
          ndef.close();
        } else {
          NdefFormatable ndefFormatable = NdefFormatable.get(tag);
          // Really should do a null test on ndefFormatable here but as the code is looking for an exception don't test for null
          ndefFormatable.connect();
          // Format at write message at the same time
          ndefFormatable.format(NdefMessage);
          ndefFormatable.close();
        }
    }

希望这应该有效，我不再使用旧的 enableForegroundDispatch API，因为它在尝试写入标签时太不可靠，enableReaderMode 要好得多。

注意，我清理了< code > readfromentin 方法。尝试从没有NDEF消息的标签中读取Ndef消息是没有意义的，因为如果标签上有Ndef消息，ACTION_NDEF_DISCOVERED总是在其他操作之前枚举。

另请注意，我还没有修复根据文档写入NdesMessage和格式的事实

不能从主应用程序线程调用它

事实上，为NFC启用ReaderMode API要好得多（除非您需要低于Android API级别19的NFC支持），因为带有此功能的标签会在单独的线程上自动处理。