NFC接待后，保持当前活动

Question

我有一个应用程序，似乎工作得很好，可以通过NFC完美地传输数据。我有一个主要活动，一个传输数据的活动，还有一个接收数据的不同活动。

发送方的活动效果很好，但当接收方获得NFC意图时，它会重新启动应用程序，使其返回到主活动。

我不确定这是为什么。我希望它拒绝任何推送，除非用户已经在那个活动中，如果他们在，留在那个活动中并处理NFC意图。

以下是清单：

<activity android:name=".MainActivity">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>
<activity android:name=".Timer" />
<activity android:name=".AddSlaves"
          android:label="Add Slave Devices"
          android:launchMode="singleTask">
    <intent-filter>
        <action android:name="android.nfc.action.NDEF_DISCOVERED" />
        <category android:name="android.intent.category.DEFAULT" />
        <data android:mimeType="text/plain" />
    </intent-filter>
</activity>
<activity android:name=".JoinSrv"
          android:launchMode="singleTask">
    <intent-filter>
        <action android:name="android.nfc.action.NDEF_DISCOVERED" />
        <category android:name="android.intent.category.DEFAULT"/>
        <data android:mimeType="text/plain" />
    </intent-filter>
</activity>

下面是sender类：

public class JoinSrv extends Activity implements NfcAdapter.OnNdefPushCompleteCallback, NfcAdapter.CreateNdefMessageCallback {
    //The array lists to hold our messages
    private ArrayList<String> messagesToSendArray = new ArrayList<>();
    private ArrayList<String> messagesReceivedArray = new ArrayList<>();

    //Text boxes to add and display our messages
    private NfcAdapter mNfcAdapter;

    //Save our Array Lists of Messages for if the user navigates away
    @Override
    public void onSaveInstanceState(@NonNull Bundle savedInstanceState) {
        super.onSaveInstanceState(savedInstanceState);
        savedInstanceState.putStringArrayList("messagesToSend", messagesToSendArray);
        savedInstanceState.putStringArrayList("lastMessagesReceived", messagesReceivedArray);
    }

    //Load our Array Lists of Messages for when the user navigates back
    @Override
    public void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        messagesToSendArray = savedInstanceState.getStringArrayList("messagesToSend");
        messagesReceivedArray = savedInstanceState.getStringArrayList("lastMessagesReceived");
    }

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


        //Check if NFC is available on device
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if (mNfcAdapter != null) {
            //Handle some NFC initialization here
        } else {
            Toast.makeText(this, "NFC not available on this device",
                    Toast.LENGTH_SHORT).show();
        }

        //Check if NFC is available on device
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if (mNfcAdapter != null) {
            //This will refer back to createNdefMessage for what it will send
            mNfcAdapter.setNdefPushMessageCallback(this, this);

            //This will be called if the message is sent successfully
            mNfcAdapter.setOnNdefPushCompleteCallback(this, this);
        }
    }

    @Override
    public NdefMessage createNdefMessage(NfcEvent event) {
        //This will be called when another NFC capable device is detected.
        //We'll write the createRecords() method in just a moment
        NdefRecord[] recordsToAttach = createRecords();
        //When creating an NdefMessage we need to provide an NdefRecord[]
        return new NdefMessage(recordsToAttach);
    }

    @Override
    public void onNdefPushComplete(NfcEvent event) {
        //This is called when the system detects that our NdefMessage was
        //Successfully sent.
        messagesToSendArray.clear();
    }

    public NdefRecord[] createRecords() {
        NdefRecord[] records = new NdefRecord[1];
        //To Create Messages Manually if API is less than
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) {

            byte[] payload = "192.168.1.100".
                    getBytes(Charset.forName("UTF-8"));
            NdefRecord record = new NdefRecord(
                    NdefRecord.TNF_WELL_KNOWN,      //Our 3-bit Type name format
                    NdefRecord.RTD_TEXT,            //Description of our payload
                    new byte[0],                    //The optional id for our Record
                    payload);                       //Our payload for the Record

            records[1] = record;

        }
        //Api is high enough that we can use createMime, which is preferred.
        else {

                byte[] payload = "192.168.1.100".
                        getBytes(Charset.forName("UTF-8"));

                NdefRecord record = NdefRecord.createMime("text/plain",payload);
                records[1] = record;

        }
        records[messagesToSendArray.size()] =
                NdefRecord.createApplicationRecord(getPackageName());
        return records;
    }

    private void handleNfcIntent(Intent NfcIntent) {
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(NfcIntent.getAction())) {
            Parcelable[] receivedArray =
                    NfcIntent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);

            if (receivedArray != null) {
                messagesReceivedArray.clear();
                NdefMessage receivedMessage = (NdefMessage) receivedArray[0];
                NdefRecord[] attachedRecords = receivedMessage.getRecords();

                for (NdefRecord record : attachedRecords) {
                    String string = new String(record.getPayload());
                    //Make sure we don't pass along our AAR (Android Application Record)
                    if (string.equals(getPackageName())) {
                        continue;
                    }
                    messagesReceivedArray.add(string);
                }
                Toast.makeText(this, "Received " + messagesReceivedArray.size() +
                        " Messages", Toast.LENGTH_LONG).show();
            } else {
                Toast.makeText(this, "Received Blank Parcel", Toast.LENGTH_LONG).show();
            }
        }
    }

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

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

以下是receiver类：

public class AddSlaves extends Activity implements NfcAdapter.OnNdefPushCompleteCallback, NfcAdapter.CreateNdefMessageCallback{
    //The array lists to hold our messages
    private ArrayList<String> messagesToSendArray = new ArrayList<>();
    private ArrayList<String> messagesReceivedArray = new ArrayList<>();

    //Text boxes to add and display our messages
    private EditText txtBoxAddMessage;
    private TextView txtReceivedMessages;
    private TextView txtMessagesToSend;
    private NfcAdapter mNfcAdapter;

    private  void updateTextViews() {
        txtReceivedMessages.setText("Messages Received:\n");
        //Populate our list of messages we have received
        if (messagesReceivedArray.size() > 0) {
            for (int i = 0; i < messagesReceivedArray.size(); i++) {
                txtReceivedMessages.append(messagesReceivedArray.get(i));
                txtReceivedMessages.append("\n");
            }
        }
    }

    //Save our Array Lists of Messages for if the user navigates away
    @Override
    public void onSaveInstanceState(@NonNull Bundle savedInstanceState) {
        super.onSaveInstanceState(savedInstanceState);
        savedInstanceState.putStringArrayList("lastMessagesReceived",messagesReceivedArray);
    }

    //Load our Array Lists of Messages for when the user navigates back
    @Override
    public void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        messagesReceivedArray = savedInstanceState.getStringArrayList("lastMessagesReceived");
    }

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

        txtReceivedMessages = (TextView) findViewById(R.id.txtMessagesReceived);
        Button btnAddMessage = (Button) findViewById(R.id.buttonAddMessage);


        //Check if NFC is available on device
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if(mNfcAdapter != null) {
            //Handle some NFC initialization here
        }
        else {
            Toast.makeText(this, "NFC not available on this device",
                    Toast.LENGTH_SHORT).show();
        }

        //Check if NFC is available on device
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if(mNfcAdapter != null) {
            //This will refer back to createNdefMessage for what it will send
            mNfcAdapter.setNdefPushMessageCallback(this, this);

            //This will be called if the message is sent successfully
            mNfcAdapter.setOnNdefPushCompleteCallback(this, this);
        }
    }

    @Override
    public NdefMessage createNdefMessage(NfcEvent event) {
        //This will be called when another NFC capable device is detected.
        return null;

    }

    @Override
    public void onNdefPushComplete(NfcEvent event) {
        //This is called when the system detects that our NdefMessage was
        //Successfully sent.
        messagesToSendArray.clear();
    }


    private void handleNfcIntent(Intent NfcIntent) {
        if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(NfcIntent.getAction())) {
            Parcelable[] receivedArray =
                    NfcIntent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);

            if(receivedArray != null) {
                messagesReceivedArray.clear();
                NdefMessage receivedMessage = (NdefMessage) receivedArray[0];
                NdefRecord[] attachedRecords = receivedMessage.getRecords();

                for (NdefRecord record:attachedRecords) {
                    String string = new String(record.getPayload());
                    //Make sure we don't pass along our AAR (Android Application Record)
                    if (string.equals(getPackageName())) { continue; }
                    messagesReceivedArray.add(string);
                }
                Toast.makeText(this, "Received " + messagesReceivedArray.size() +
                        " Messages", Toast.LENGTH_LONG).show();
                updateTextViews();
            }
            else {
                Toast.makeText(this, "Received Blank Parcel", Toast.LENGTH_LONG).show();
            }
        }
    }


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

    @Override
    public void onResume() {
        super.onResume();
        updateTextViews();
        handleNfcIntent(getIntent());
    }
}

Answer 1

您的发件人活动html" target="_blank">代码中有几个问题：

>

你存储了MessagesToSendArray，但是你从来没有用数据填充这个数组列表（即MessagesToSendArray.size（）总是0）。由于每当调用createNDefMessage（）时，您都会新鲜创建NDEF消息，因此无需保存和恢复MessagesToSendArray。

您写道希望在一个活动中发送NDEF消息，但希望在另一个活动中接收NFC事件。但是，您注册了发件人活动以接收清单中的NDEF_发现事件。如果您不想接收和处理这些事件，则无需在清单中使用NDEF_发现的意图过滤器。

此外，无需在发送方活动中处理NDEF_发现的意图（即，您可以安全地删除方法onNewIntent（）和handleNfcIntent（））。

在果冻豆下面的Android版本上，您创建了一个结构无效的NFC论坛文本记录。文本RTD请求一个以表单编码的有效负载（也请参阅这篇文章）

+----------+---------------+--------------------------------------+
| Status   | Language Code | Text                                 |
| (1 byte) | (n bytes)     | (m bytes)                            |
+----------+---------------+--------------------------------------+

public static NdefRecord createTextRecord(String language, String text) {
    byte[] languageBytes;
    byte[] textBytes;
    try {
        languageBytes = language.getBytes("US-ASCII");
        textBytes = text.getBytes("UTF-8");
    } catch (UnsupportedEncodingException e) {
        throw new AssertionError(e);
    }

    byte[] recordPayload = new byte[1 + (languageBytes.length & 0x03F) + textBytes.length];

    recordPayload[0] = (byte)(languageBytes.length & 0x03F);
    System.arraycopy(languageBytes, 0, recordPayload, 1, languageBytes.length & 0x03F);
    System.arraycopy(textBytes, 0, recordPayload, 1 + (languageBytes.length & 0x03F), textBytes.length);

    return new NdefRecord(NdefRecord.TNF_WELL_KNOWN, NdefRecord.RTD_TEXT, null, recordPayload);
}

我不清楚为什么你在果冻豆以下的Android版本上创建一个NFC论坛文本记录，而在果冻豆及以上版本上创建一个MIME类型记录。您应该保持一致，并在所有平台上创建相同的记录类型（请参见方法NDefRecord.create文本记录（“en”，“字符串”），不低于API级别21）：

String text = "192.168.1.100";
String language = "en";

NdefRecord record;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
    record = NdefRecord.createTextRecord(language, text);
} else {
    record = createTextRecord(language, text);
}

最后，在createRecords（）中创建数组recordsas

NdefRecord[] records = new NdefRecord[1];

因此，数组中有一个元素可以在索引0处访问。Hoever，稍后尝试访问元素1：

records[1] = record;

这将导致一个IndexOutOfBound异常。由于Android通过createNDefMessage（）回调调用了createNotes（），因此回调失败（由于运行时异常），Android将不会使用您的NDEF消息。相反，Android将为您的应用使用默认的NDEF消息。此默认NDEF消息包含一个Android应用程序记录，该记录将导致您的主活动被调用（因为您的其他活动都没有注册为默认NDEF消息的特定内容而被启动）；请参见NFC标签检测不是调用NewIntent，而是从主活动启动。因此，您需要将记录中存储新创建的NDEF记录的偏移量更改为0：

records[0] = record;

此外，您需要删除该行

records[messagesToSendArray.size()] =
    NdefRecord.createApplicationRecord(getPackageName());

因为这将用Android应用程序记录覆盖以前存储在索引0处的NDEF记录（MessagesToSendArray.size（）为0）。同样，这将导致您的主要活动被启动，因为您没有在清单中注册特定的记录类型。

最后，如果您想拒绝推送，除非用户在接收者活动中，您应该考虑使用前台调度系统。在这种情况下，您将完成从清单中删除所有NDEF_DISCOVERED意图过滤器，并用前台调度系统注册每个活动（接收者、发送者和主）。在接收者中，您将通过onNewIntent（）接收NDEF消息。在发送者和主活动中，您只需忽略并删除任何收到的NDEF消息。有关示例，请参阅Android应用程序仅为一个活动启用NFC。