getActiveNotifications() using NotificationListenerService

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="testapp.android.gradle.inutilfutil.com.myapplication">

    <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/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <service
            android:name=".MyNotificationService"
            android:permission="android.permission.BIND_NOTIFICATION_LISTENER_SERVICE"
            android:enabled="true"
            android:exported="true">

            <intent-filter>
                <action android:name="android.service.notification.NotificationListenerService" />
            </intent-filter>
        </service>
    </application>

</manifest>

MainActivity.java

package testapp.android.gradle.inutilfutil.com.myapplication;

import android.app.NotificationManager;
import android.content.ComponentName;
import android.content.Intent;
import android.provider.Settings;
import android.service.notification.NotificationListenerService;
import android.service.notification.StatusBarNotification;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {
    public static final String TAG = "MainActivity";
    private static final String ACTION_NOTIFICATION_LISTENER_SETTINGS = "android.settings.ACTION_NOTIFICATION_LISTENER_SETTINGS";


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public void onStart() {
        showNotifications();
        super.onStart();
    }

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

    public void showNotifications() {
        if (isNotificationServiceEnabled()) {
            Log.i(TAG, "Notification enabled -- trying to fetch it");
            getNotifications();
        } else {
            Log.i(TAG, "Notification disabled -- Opening settings");
            startActivity(new Intent(ACTION_NOTIFICATION_LISTENER_SETTINGS));
        }
    }

    public void getNotifications() {
        Log.i(TAG, "Waiting for MyNotificationService");
        MyNotificationService myNotificationService = MyNotificationService.get();
        Log.i(TAG, "Active Notifications: [");
        for (StatusBarNotification notification : myNotificationService.getActiveNotifications()) {
            Log.i(TAG, "    " + notification.getPackageName() + " / " + notification.getTag());
        }
        Log.i(TAG, "]");
    }

    private boolean isNotificationServiceEnabled(){
        String pkgName = getPackageName();
        final String allNames = Settings.Secure.getString(getContentResolver(), "enabled_notification_listeners");
        if (allNames != null && !allNames.isEmpty()) {
            for (String name : allNames.split(":")) {
                if (getPackageName().equals(ComponentName.unflattenFromString(name).getPackageName())) {
                    return true;
                }
            }
        }
        return false;
    }
}

MyNotificationService.java

package testapp.android.gradle.inutilfutil.com.myapplication;

import android.service.notification.NotificationListenerService;
import android.service.notification.StatusBarNotification;
import android.util.Log;

import java.util.concurrent.Semaphore;

public class MyNotificationService extends NotificationListenerService {
    private static final String TAG = "MyNotificationService";
    static MyNotificationService _this;
    static Semaphore sem = new Semaphore(0);

    public static MyNotificationService get() {
        sem.acquireUninterruptibly();
        MyNotificationService ret = _this;
        sem.release();
        return ret;
    }

    @Override
    public void onListenerConnected() {
        Log.i(TAG, "Connected");
        _this = this;
        sem.release();
    }

    @Override
    public void onListenerDisconnected() {
        Log.i(TAG, "Disconnected");
        sem.acquireUninterruptibly();
        _this = null;
    }

    @Override
    public void onNotificationPosted(StatusBarNotification sbn) {

    }

    @Override
    public void onNotificationRemoved(StatusBarNotification sbn) {
        super.onNotificationRemoved(sbn);
    }
}

I have absolutely no memory of writing this, or why 🤣

I took a look at it briefly -- Have you tried requestRebind()? -- https://developer.android.com/reference/android/service/notification/NotificationListenerService.html#requestRebind(android.content.ComponentName)

Alternatively, the implementation seems to be exactly the same as calling NotificationManager.getActiveNotifications() -- I imagine that enabling the NotificationService adds the missing permissions to the package.