NFC 读取不工作

Question

我是开发 Android 应用程序的新手。目前我正在尝试开发自己的标签阅读器，可以读取 MiFare Ultralight 标签。

但我无法读取标签，因为 NfcAdapter.ACTION_TECH_DISCOVERED.equals(action) 总是返回 false。有人可以帮我吗？

NfcReader.java

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mText = (TextView) findViewById(R.id.text);
    mText.setText("Scan a tag");

    mAdapter = NfcAdapter.getDefaultAdapter();

    // Create a generic PendingIntent that will be deliver to this activity. The NFC stack
    // will fill in the intent with the details of the discovered tag before delivering to
    // this activity.
    mPendingIntent = PendingIntent.getActivity(this, 0,
            new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);

    // Setup an intent filter for all MIME based dispatches
    IntentFilter ndef = new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED);
    try {
        ndef.addDataType("*/*");
    } catch (MalformedMimeTypeException e) {
        throw new RuntimeException("fail", e);
    }
    mFilters = new IntentFilter[] {
            ndef,
    };

    // Setup a tech list for all NfcF tags
    mTechLists = new String[][] { new String[] { NfcF.class.getName() } };

    Intent intent = getIntent();

    getNdefMessages(intent);
}

public void getNdefMessages(Intent intent) {
    // Parse the intent
    NdefMessage[] msgs = null;
    String action = intent.getAction();
    if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {
        Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
        if (rawMsgs != null) {
            msgs = new NdefMessage[rawMsgs.length];
            for (int i = 0; i < rawMsgs.length; i++) {
                msgs[i] = (NdefMessage) rawMsgs[i];
            }
        }
        else {
        // Unknown tag type
            byte[] empty = new byte[] {};
            NdefRecord record = new NdefRecord(NdefRecord.TNF_UNKNOWN, empty, empty, empty);
            NdefMessage msg = new NdefMessage(new NdefRecord[] {record});
            msgs = new NdefMessage[] {msg};
        }
    }        
    else {
        //Log.e(TAG, "Unknown intent " + intent);
        finish();
    }
}

@Override
public void onResume() {
    super.onResume();
    mAdapter.enableForegroundDispatch(this, mPendingIntent, mFilters, mTechLists);
}

@Override
public void onNewIntent(Intent intent) {
    Log.i("Foreground dispatch", "Discovered tag with intent: " + intent);
    getNdefMessages(intent);            
}

@Override
public void onPause() {
    super.onPause();
    //mAdapter.disableForegroundDispatch(this);
    throw new RuntimeException("onPause not implemented to fix build");
}

Manifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.nfc.reader"
      android:versionCode="1"
      android:versionName="1.0">

    <uses-permission android:name="android.permission.NFC" />
    <uses-sdk android:minSdkVersion="10"/>
    <uses-feature android:name="android.hardware.nfc" android:required="true" />

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name="NfcReader"
            android:theme="@android:style/Theme.NoTitleBar">
            <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.TECH_DISCOVERED"/>
                <data android:mimeType="text/plain" />
                <category android:name="android.intent.category.DEFAULT"/>
            </intent-filter>

            <meta-data android:name="android.nfc.action.TECH_DISCOVERED"
                android:resource="@xml/nfctech" />
        </activity>

    </application>

</manifest> 

Answer 1

当检测到带有 NDEF 消息的标签时，android 会查找任何具有带有意图过滤器的 Activity 的应用程序，以执行操作“android.nfc.action.NDEF_DISCOVERED”。如果两个或多个应用程序可以处理此操作，则具有最精确过滤器的应用程序会接收意图。当找到具有相同过滤器的应用程序时，用户会选择其中一个。因此，在 AndroidManifest.xml 中，您必须使用此操作来检测 NDEF 格式的标签。

如果您想阅读 NDEF 消息，不必担心您正在阅读的标签类型（Ultralight、Felica、Topaz...）。 Android 使用 android.nfc.tech.Ndef 来调度 NDEF 格式的标签。因此，当您的 Activity 位于前台时，要获取所有 NdefMessage，您可以使用以下代码片段：

//Called in onCreate()
private void nfcConfig() {
    mAdapter = NfcAdapter.getDefaultAdapter(this);
    pendingIntent = PendingIntent.getActivity(
            this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
    techListsArray = new String[][]{new String[]{
                Ndef.class.getName()
            }};     
}

@Override
public void onResume() {
    super.onResume();
    mAdapter.enableForegroundDispatch(this, pendingIntent, null, techListsArray);
}

@Override
public void onPause() {
    super.onPause();
    mAdapter.disableForegroundDispatch(this);
}

@Override
public void onNewIntent(Intent intent) {
    getNdefMessages(intent);            
}

如果您想读取 Ultralight 标签（或其他技术），那应该是因为您需要来自该标签的原始数据。它不能从主应用程序线程执行。例如：

private void nfcConfig(){
...
//Mifare Ultralight filter
techListsArray = new String[][]{new String[]{
            NfcA.class.getName(),
            MifareUltralight.class.getName()
        }};
...
}

@Override
public void onNewIntent(Intent intent) {
    getRawData(intent);            
}

private void getRawData(Intent intent){
    final Tag tag = (Tag) intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
    MifareUltralight ulTag = MifareUltralight.getTag();
    new ReadMFULTask(ulTag).execute();
}

private static class ReadMFULTask extends AsyncTask<Void, Void, Void> {

    private Tag mTag;

    public ReadMFULTask(Tag tag){
        mTag = tag;
    }

    @Override
    protected Void doInBackground(Void... arg0) {

    MifareUltralight ulTag = MifareUltralight.get(mTag);
    try {
        ulTag.connect();
            //Read all pages from an Ul tag
            for(int i=0; i < 16; i=i+4){
            byte[] data = ulTag.readPages(i);
                String dataString = HexUtilities.getHexString(data);
                Log.d("RAW DATA", dataString);
            }
            ulTag.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

Answer 2

在代码中，您根据 ACTION_TECH_DISCOVERED 设置意图过滤器，但随后尝试 ndef.addDataType(/)，这是为 ACTION_NDEF_DISCOVERED 设置意图过滤器的方法。相反，您可以简单地执行以下操作：

IntentFilter ntech = new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED);
mFilters = new IntentFilter[]{ ntech };

确保您已正确设置 nfc_tech_list.xml：

<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
    <tech-list>
        <tech>android.nfc.tech.NfcA</tech>
        <tech>android.nfc.tech.MifareUltralight</tech>
    </tech-list>
</resources>