Android implements the function of floating buttons

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/**
  * MainActivity: Used to request permissions and start/stop FloatingService
  */
public class MainActivity extends AppCompatActivity {
 
    private static final int REQ_OVERLAY = 1000;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        (savedInstanceState);
        setContentView(.activity_main);
 
		// Activate the floating button        findViewById(.btn_start).setOnClickListener(v -> {
            if ((this)) {
                startService(new Intent(this, ));
                finish(); // Optional: Turn off the Activity, the floating button will still be displayed            } else {
                // Request floating window permissions                Intent intent = new Intent(
                  Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
                  ("package:" + getPackageName()));
                startActivityForResult(intent, REQ_OVERLAY);
            }
        });
 
		// Stop the floating button        findViewById(.btn_stop).setOnClickListener(v -> {
            stopService(new Intent(this, ));
        });
    }
 
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQ_OVERLAY) {
            if ((this)) {
                startService(new Intent(this, ));
            } else {
                (this, "No floating window permission granted", Toast.LENGTH_SHORT).show();
            }
        }
    }
}
 
/**
  * FloatingService: Front Service, add drag-and-drop floating buttons
  */
public class FloatingService extends Service {
 
    private WindowManager windowManager;
    private View floatView;
    private  params;
 
    @Override
    public void onCreate() {
        ();
        // 1. Create a front desk notification        String channelId = createNotificationChannel();
        Notification notification = new (this, channelId)
            .setContentTitle("Floating Button")
            .setContentText("The floating button is activated")
            .setSmallIcon(.ic_floating)
            .setOngoing(true)
            .build();
        startForeground(1, notification);
 
        // 2. Initialize WindowManager and LayoutParams        windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
        params = new ();
          = .WRAP_CONTENT;
         = .WRAP_CONTENT;
         = ;
          = .FLAG_NOT_FOCUSABLE
                      | .FLAG_LAYOUT_IN_SCREEN;
        // Support for levitation types by different SDKs        if (.SDK_INT >= Build.VERSION_CODES.O) {
             = .TYPE_APPLICATION_OVERLAY;
        } else {
             = .TYPE_PHONE;
        }
        // Default initial position         =  | ;
         = 100;
         = 300;
 
        // 3. Load custom layout        floatView = (this)
                      .inflate(.floating_view, null);
        ImageView iv = (.iv_float);
        (new FloatingOnTouchListener());
 
        // 4. Add to window        (floatView, params);
    }
 
    // Front Desk Notification Channel    private String createNotificationChannel() {
        String channelId = "floating_service";
        if (.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel chan = new NotificationChannel(
                channelId, "Hanging Button Service",
                NotificationManager.IMPORTANCE_NONE);
            ((NotificationManager)getSystemService(NOTIFICATION_SERVICE))
                .createNotificationChannel(chan);
        }
        return channelId;
    }
 
    @Override
    public void onDestroy() {
        ();
        if (floatView != null) {
            (floatView);
            floatView = null;
        }
    }
 
    @Nullable @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
 
    /**
      * Touch monitoring: Support drag and click
      */
    private class FloatingOnTouchListener implements  {
        private int initialX, initialY;
        private float initialTouchX, initialTouchY;
        private long touchStartTime;
 
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (()) {
                case MotionEvent.ACTION_DOWN:
                    // Record the data when pressed                    initialX = ;
                    initialY = ;
                    initialTouchX = ();
                    initialTouchY = ();
                    touchStartTime = ();
                    return true;
                case MotionEvent.ACTION_MOVE:
                    // Update the suspended position                     = initialX + (int)(() - initialTouchX);
                     = initialY + (int)(() - initialTouchY);
                    (floatView, params);
                    return true;
                case MotionEvent.ACTION_UP:
                    long clickDuration = () - touchStartTime;
                    // If the press and lift positions do not change much and the time is short, it will be considered a click                    if (clickDuration < 200 
                        && (() - initialTouchX,
                                      () - initialTouchY) < 10) {
                        (,
                            "The floating button is clicked!", Toast.LENGTH_SHORT).show();
                        // Activity or other operations can be started here                    }
                    return true;
            }
            return false;
        }
    }
}

<!-- ===================================================================
      — Entrance、Permissions and Service statement
=================================================================== -->
<manifest xmlns:andro
    package="">
    <!-- Floating window permissions -->
    <uses-permission android:name=".SYSTEM_ALERT_WINDOW"/>
    <application ...>
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name=""/>
                <category android:name=""/>
            </intent-filter>
        </activity>
        <!-- statement Service -->
        <service android:name=".FloatingService"
                 android:exported="false"/>
    </application>
</manifest>

<!-- ===================================================================
     activity_main.xml — Includes startup/Stop button
=================================================================== -->
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:andro
    android:
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    android:padding="24dp">
 
    <Button
        android:
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start the floating button"/>
 
    <Button
        android:
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Stop floating button"
        android:layout_marginTop="16dp"/>
</LinearLayout>

<!-- ===================================================================
     floating_view.xml — Floating button layout
=================================================================== -->
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:andro
    android:layout_width="48dp"
    android:layout_height="48dp">
 
    <ImageView
        android:
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@drawable/ic_float"
        android:background="@drawable/float_bg"
        android:padding="8dp"/>
</FrameLayout>

<!-- ===================================================================
     float_bg.xml — Button background（Circular + shadow）
=================================================================== -->
<shape xmlns:andro
    android:shape="oval">
    <solid android:color="#FFFFFF"/>
    <size android:width="48dp" android:height="48dp"/>
    <corners android:radius="24dp"/>
    <padding android:all="4dp"/>
    <stroke android:width="1dp" android:color="#CCCCCC"/>
    <!-- shadow需在代码中或 ShadowLayer Settings in -->
</shape>