android {
    defaultConfig {
        ...
        minSdk 21
    }

2. Ensure the mavenCentral() repository is declared in the project-level build.gradle/setting.gradle file:

   settings.gradle

   pluginManagement {
       repositories {
           ...
           mavenCentral()
       }
   }
   dependencyResolutionManagement {
       ...
       repositories {
           ...
           mavenCentral()
       }
   }
   

   build.gradle (project-level) (on old gradle versions)

       allprojects {
           repositories {
               mavenCentral()
               ...
           }
           ...
       }
   

Java docs is not completed yet because the author is (really) busy and (a little) tired 😪

class MyService: ExpandableBubbleService() {

    override fun onCreate() {
        super.onCreate()
        minimize()
    }

   // optional, only required if you want to call minimize()
   override fun configBubble(): BubbleBuilder? {
       return ...
   }

   // optional, only required if you want to call expand()
   override fun configExpandedBubble(): ExpandedBubbleBuilder? {
       return ...
   }
}

    <!-- these two permissions are added by default -->
    <!-- <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/> -->
    <!-- <uses-permission android:name="android.permission.FOREGROUND_SERVICE"/> -->

    <application>
        ...
        <service android:name="<YOUR_PACKAGE>.MyService" />

    </application>

    Intent intent = new Intent(context, MyService.class);
    
    ContextCompat.startForegroundService(this, intent);
    // or
    // startService(intent);           // for android version lower than 8.0 (android O)
    // startForegroundService(intent); // for android 8.0 and higher

    val intent = Intent(context, MyService::class.java)
    
    ContextCompat.startForegroundService(this, intent)
    // or
    // startService(intent)           // for android version lower than 8.0 (android O)
    // startForegroundService(intent) // for android 8.0 and higher

public class MyServiceJava extends ExpandableBubbleService {

    @Override
    public void onCreate() {
        super.onCreate();
        minimize();
    }

    @Nullable
    @Override
    public BubbleBuilder configBubble() {
        View imgView = ViewHelper.fromDrawable(this, R.drawable.ic_rounded_blue_diamond, 60, 60);
        imgView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                expand();
            }
        });
        return new BubbleBuilder(this)
                .bubbleView(imgView)
                .bubbleStyle(R.style.default_bubble_style)
                .bubbleDraggable(true)
                .forceDragging(true)
                .closeBubbleView(ViewHelper.fromDrawable(this, R.drawable.ic_close_bubble))
                .closeBubbleStyle(R.style.default_close_bubble_style)
                .distanceToClose(100)
                .triggerClickablePerimeterPx(5f)
                .closeBehavior(CloseBubbleBehavior.FIXED_CLOSE_BUBBLE)
                .startLocation(100, 100)
                .enableAnimateToEdge(true)
                .bottomBackground(false)
                .addFloatingBubbleListener(new FloatingBubbleListener() {
                    @Override
                    public void onFingerDown(float x, float y) {}
                    @Override
                    public void onFingerUp(float x, float y) {}
                    @Override
                    public void onFingerMove(float x, float y) {}
                })
                ;
                
    }

    @Nullable
    @Override
    public ExpandedBubbleBuilder configExpandedBubble() {
        View expandedView = LayoutInflater.from(this).inflate(R.layout.layout_view_test, null);

        expandedView.findViewById(R.id.btn).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                minimize();
            }
        });
        return new ExpandedBubbleBuilder(this)
                .expandedView(expandedView)
                .startLocation(0, 0)
                .draggable(true)
                .style(R.style.default_bubble_style)
                .fillMaxWidth(true)
                .enableAnimateToEdge(true)
                .dimAmount(0.5f);
    }
}

class MyServiceKt : ExpandableBubbleService() {

    override fun onCreate() {
        super.onCreate()
        minimize()
    }

    override fun configBubble(): BubbleBuilder? {
        val imgView = ViewHelper.fromDrawable(this, R.drawable.ic_rounded_blue_diamond, 60, 60)
        imgView.setOnClickListener {
            expand()
        }

        return BubbleBuilder(this)
            
            // set bubble view
            .bubbleView(imgView)
            
            // or our sweetie, Jetpack Compose
            .bubbleCompose {
                BubbleCompose()
            }
            
            // set style for the bubble, fade animation by default
            .bubbleStyle(null)
            
            // set start location for the bubble, (x=0, y=0) is the top-left
            .startLocation(100, 100)    // in dp
            .startLocationPx(100, 100)  // in px
            
            // enable auto animate bubble to the left/right side when release, true by default
            .enableAnimateToEdge(true)
            
            // set close-bubble view
            .closeBubbleView(ViewHelper.fromDrawable(this, R.drawable.ic_close_bubble, 60, 60))
            
            // set style for close-bubble, null by default
            .closeBubbleStyle(null)
            
            // DYNAMIC_CLOSE_BUBBLE: close-bubble moving based on the bubble's location
            // FIXED_CLOSE_BUBBLE (default): bubble will automatically move to the close-bubble when it reaches the closable-area
            .closeBehavior(CloseBubbleBehavior.DYNAMIC_CLOSE_BUBBLE)
            
            // the more value (dp), the larger closeable-area
            .distanceToClose(100)
            
            // enable bottom background, false by default
            .bottomBackground(true)
            
            .addFloatingBubbleListener(object : FloatingBubbleListener {
                override fun onFingerMove(x: Float, y: Float) {} // The location of the finger on the screen which triggers the movement of the bubble.
                override fun onFingerUp(x: Float, y: Float) {}   // ..., when finger release from bubble
                override fun onFingerDown(x: Float, y: Float) {} // ..., when finger tap the bubble
            })

            // set the clickable perimeter of the bubble in pixels (default = 5f)
            .triggerClickablePerimeterPx(5f)

    }

    override fun configExpandedBubble(): ExpandedBubbleBuilder? {

        val expandedView = LayoutInflater.from(this).inflate(R.layout.layout_view_test, null)
        expandedView.findViewById<View>(R.id.btn).setOnClickListener {
            minimize()
        }

        return ExpandedBubbleBuilder(this)
            .expandedView(expandedView)
            .expandedCompose { 
                ExpandedCompose()
            }
            // handle key code
            .onDispatchKeyEvent {
                if(it.keyCode == KeyEvent.KEYCODE_BACK){
                    minimize()
                }
                null
            }
            // set start location in dp
            .startLocation(0, 0)
            // allow expanded bubble can be draggable or not
            .draggable(true)
            // fade animation by default
            .style(null)
            // 
            .fillMaxWidth(true)
            // animate to the left/right side when release, trfalseue by default 
            .enableAnimateToEdge(true)
            // set background dimmer
            .dimAmount(0.6f)
    }
}

public class MyService extends ExpandableBubbleService {
    ...
    @Override
    public void startNotificationForeground() {
        startForeground(...);

        // or you can use NotificationHelper class
        // val noti = NotificationHelper(this)
        // noti.createNotificationChannel()
        // startForeground(noti.notificationId, noti.defaultNotification())
    }
}

class MyService : FloatingBubbleService() {
    ...
    // optional, of course
    override fun startNotificationForeground() {
        startForeground(...)

        // or you can use NotificationHelper class
        // val noti = NotificationHelper(this)
        // noti.createNotificationChannel()
        // startForeground(noti.notificationId, noti.defaultNotification())
    }
}

Starting in Android 13 (API level 33), notifications are only visible if the "POST_NOTIFICATIONS" permission is granted.

The service will run normally even if the notification is not visible. 🍀

You still need to initialize the notification before showing any view.