Android:如何禁止在扫描 NFC 标签时重新打开您的应用程序？

Question

我正在编写一个从 Mifare Classic 卡 (4k) 读取数据的 Android 应用程序。我已经编辑了我的 AndroidManifest.xml 文件，以便应用程序启动(或者我可以选择另一个使用 NFC 的应用程序)。但是当我的应用程序是开放式的并且我将我的卡放在手机旁边时，它会再次弹出窗口，我可以在其中选择要打开的应用程序。经过一些研究，我发现我需要编辑函数:onNewIntent，因为这是在您的应用程序运行时扫描标签时调用的函数。

这是我的代码:(当我扫描我的卡时，handleIntent 函数第二行的 toast 显示为:ACTION_TECH_DISCOVERED。)

package be.khleuven.aanwezigheidssysteem;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.Intent;
import android.content.IntentFilter;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.Ndef;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;
import android.content.IntentFilter.MalformedMimeTypeException;

import java.io.UnsupportedEncodingException;
import java.util.Arrays;




public class Login extends Activity {
public static final String MIME_TEXT_PLAIN = "text/plain";
public static final String TAG = "NfcDemo";

private TextView mTextView;
private NfcAdapter mNfcAdapter;

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

    mTextView = (TextView) findViewById(R.id.textView_explanation);

    mNfcAdapter = NfcAdapter.getDefaultAdapter(this);


    if (mNfcAdapter == null) {
        // Stop here, we definitely need NFC
        Toast.makeText(this, "This device doesn't support NFC.", Toast.LENGTH_LONG).show();
        //finish();
        return;

    }

    if (!mNfcAdapter.isEnabled()) {
        mTextView.setText("NFC is disabled.");
    } else {
        mTextView.setText(R.string.explanation);
    }

    handleIntent(getIntent());
}

@Override
protected void onResume() {
    super.onResume();

    /**
     * It's important, that the activity is in the foreground (resumed). Otherwise
     * an IllegalStateException is thrown.
     */
    setupForegroundDispatch(this, mNfcAdapter);
}

@Override
protected void onPause() {
    /**
     * Call this before onPause, otherwise an IllegalArgumentException is thrown as well.
     */
    stopForegroundDispatch(this, mNfcAdapter);

    super.onPause();
}

@Override
public void onNewIntent(Intent intent) {
    /**
     * This method gets called, when a new Intent gets associated with the current activity instance.
     * Instead of creating a new activity, onNewIntent will be called. For more information have a look
     * at the documentation.
     *
     * In our case this method gets called, when the user attaches a Tag to the device.
     */
    handleIntent(intent);
}

private void handleIntent(Intent intent) {
    String action = intent.getAction();
    Toast.makeText(this, action, Toast.LENGTH_LONG).show();
    if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {

        String type = intent.getType();
        if (MIME_TEXT_PLAIN.equals(type)) {

            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
            new NdefReaderTask().execute(tag);

        } else {
            Log.d(TAG, "Wrong mime type: " + type);
        }
    } else if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(action)) {
        Toast.makeText(this, "Ze zijn gelijk", Toast.LENGTH_LONG).show();
        // In case we would still use the Tech Discovered Intent
        Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
        String[] techList = tag.getTechList();
        String searchedTech = Ndef.class.getName();

        for (String tech : techList) {
            if (searchedTech.equals(tech)) {
                new NdefReaderTask().execute(tag);
                break;
            }
        }
        TextView t = (TextView) findViewById(R.id.textView_explanation);
        t.setText("Mooi kaartje heb je daar");
    }

    else if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action)) {

        // In case we would still use the Tech Discovered Intent
        Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
        String[] techList = tag.getTechList();
        String searchedTech = Ndef.class.getName();

        for (String tech : techList) {
            if (searchedTech.equals(tech)) {
                new NdefReaderTask().execute(tag);
                break;
            }
        }
    }
    if (NfcAdapter.ACTION_TECH_DISCOVERED.equals(intent.getAction())) {
        TextView textView = (TextView) findViewById(R.id.textView_explanation);
        textView.setText("Hello NFC tag!");
    } else {
        // ignore
    }

}

public static void setupForegroundDispatch(final Activity activity, NfcAdapter adapter) {
    final Intent intent = new Intent(activity.getApplicationContext(), activity.getClass());
    intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);

    final PendingIntent pendingIntent = PendingIntent.getActivity(activity.getApplicationContext(), 0, intent, 0);

    IntentFilter[] filters = new IntentFilter[1];
    String[][] techList = new String[][]{};

    // Notice that this is the same filter as in our manifest.
    filters[0] = new IntentFilter();
    filters[0].addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
    filters[0].addCategory(Intent.CATEGORY_DEFAULT);
    try {
        filters[0].addDataType(MIME_TEXT_PLAIN);
    } catch (MalformedMimeTypeException e) {
        throw new RuntimeException("Check your mime type.");
    }

    adapter.enableForegroundDispatch(activity, pendingIntent, filters, techList);
}

public static void stopForegroundDispatch(final Activity activity, NfcAdapter adapter) {
    adapter.disableForegroundDispatch(activity);
}

private class NdefReaderTask extends AsyncTask<Tag, Void, String> {

    @Override
    protected String doInBackground(Tag... params) {
        Tag tag = params[0];

        Ndef ndef = Ndef.get(tag);
        if (ndef == null) {
            // NDEF is not supported by this Tag.
            return null;
        }

        NdefMessage ndefMessage = ndef.getCachedNdefMessage();

        NdefRecord[] records = ndefMessage.getRecords();
        for (NdefRecord ndefRecord : records) {
            if (ndefRecord.getTnf() == NdefRecord.TNF_WELL_KNOWN && Arrays.equals(ndefRecord.getType(), NdefRecord.RTD_TEXT)) {
                try {
                    return readText(ndefRecord);
                } catch (UnsupportedEncodingException e) {
                    Log.e(TAG, "Unsupported Encoding", e);
                }
            }
        }

        return null;
    }

}
}

Answer 1

您已经注册了前台调度系统。当您的应用程序是前台应用程序时，您通常会通过这种方式让您的应用程序优先于其他已注册的应用程序。但是，您只为包含以文本记录(或文本/纯文本类型的 MIME 类型记录)开头的 NDEF 消息的标签注册了前台调度，这似乎不适用于您的标签:

filters[0].addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
filters[0].addCategory(Intent.CATEGORY_DEFAULT);
filters[0].addDataType(MIME_TEXT_PLAIN);

相反，您可以注册以使用前台调度系统捕获任何标签(稍后您可以静默删除您不感兴趣的标签):

public static void setupForegroundDispatch(final Activity activity, NfcAdapter adapter) {
    final Intent intent = new Intent(activity, activity.getClass());
    intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);

    final PendingIntent pendingIntent = PendingIntent.getActivity(activity, 0, intent, 0);

    adapter.enableForegroundDispatch(activity, pendingIntent, null, null);
}

或者，您可以使用 NfcAdapter.enableForegroundDispatch() 方法的最后两个参数注册更具体的类型。