找到NFC标签后，活动将重新打开

Question

I'm developing an app that should detect NFC tags. My problem is that my activity reopens every time the app scans a tag. It should just open when the app is closed. But when it is active, I just want the data from the tag.

Manifest:

?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.corinna.nfc_testapp" >

<uses-permission android:name="android.permission.NFC" />
<uses-sdk android:minSdkVersion="14"/>
<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:supportsRtl="true"
    android:theme="@style/AppTheme" >
    <activity
        android:name=".MainActivity"
        android:label="@string/app_name"
        android:theme="@style/AppTheme.NoActionBar"
        >
        <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>
    </activity>
</application>

</manifest>

Activity onCreate & handleIntent

rotected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

    //Fragment ReadOrWrite
    fRead = (Fragment_Read) Fragment.instantiate(getApplicationContext(), Fragment_Read.class.getName(), null);
    Fragment_ReadOrWrite fReadOrWrite = (Fragment_ReadOrWrite) Fragment.instantiate(getApplicationContext(), Fragment_ReadOrWrite.class.getName(), null);
    fReadOrWrite.setFragment_Read(fRead);
    FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.id_activity_main, fReadOrWrite);
    fragmentTransaction.commit();


    //NFC

    mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

    handleIntent(getIntent());
}

private void handleIntent(Intent intent) {
    String action = intent.getAction();
    if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(action)) {

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

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

        } else {
            System.out.println("Wrong mime type: " + type);
        }
    }
}

Answer 1

Just use launchMode="singleTop" in your main activity manifest. This will ensure that if your activity is at the top of your task stack, it will not be recreated.

Be aware that onCreate is no longer called in this case, so if you want to read the content from intent, you need to override the onNewIntent Activity method.