空NFC标签读写Android应用程序.手机在扫描空标签时返回自己的消息，但应用程序不工作

Question

我已经在NFC TAG上进行了读写应用程序。但是，当我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我的应用程序Toast消息"；标记为空；。但是，当我关闭我的应用程序时，我会收到手机短信。

基本上，我需要以下帮助：

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。

AndroidManifest.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标记，请更改您的"；nfc_tech_filter.xml"；文件到下面的文件：-

<?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，当检测到NdefFormatable标签时，你的应用程序会说它想要得到通知，这将阻止你看到安卓操作系统在显示其中一个标签时显示它自己的消息。(如果出现永远无法存储Ndef消息的标签，操作系统仍将显示消息(

然后重构处理系统传递给应用程序的意图，以处理通过标签的

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();
}
}

希望这能起作用，我不再使用旧的enableForegroundDispatchAPI，因为它在尝试写入标签时太不可靠了，enableReaderMode要好得多。

注意：我清理了readFromIntent方法，尝试从没有Ndef消息的标签读取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。

还要注意的是，我还没有根据文档修复writeNdefMessage和format这一事实

它不能从主应用程序线程调用

实际上，为NFC启用ReaderMode API要好得多(除非你需要低于Android API 19级的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。