如何解决NFC读取无效
| 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读取器，它可以读取MiFare Ultralight标签。 但是我无法读取标签，因为NfcAdapter.ACTION_TECH_DISCOVERED.equals（action）始终返回false。有人可以帮我吗？ NfcReader.javapublic 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,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);
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 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>
解决方法
当检测到带有NDEF消息的标签时，Android会查找具有“活动”和“意图”过滤器的所有应用程序，以执行操作“ android.nfc.action.NDEF_DISCOVERED”。如果两个或更多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将收到此意图。当找到具有相同过滤器的应用程序时，是选择一个的用户。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，则不必担心您正在阅读哪种标签（Ultralight，Felica，Topaz等）。 Android使用android.nfc.tech.Ndef来分发NDEF格式的标签。因此，要在活动处于前台时获取所有NdefMessages，可以使用以下代码段：
//Called in onCreate()
private void nfcConfig() {
mAdapter = NfcAdapter.getDefaultAdapter(this);
pendingIntent = PendingIntent.getActivity(
this,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);
}
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;
}
}
IntentFilter ntech = new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED);
mFilters = new IntentFilter[]{ ntech };
<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>
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