How to create an 'Always on top overlay' in Android

I'd started an Android project, and I need to create a small image button that is always on top of all applications. I have seen some other apps doing that, and I want it to be like those. It should be movable in the screen (for example, like YouTube or Telegram's video overlays) and should be destroyable too.

I also would like to handle the clicks on my image overlay.

So far I've followed some other tutorials and I have granted the Settings.ACTION_MANAGE_OVERLAY_PERMISSION permission. But I don't know what to do after that.

Any helps would be greatly appreciated

Alright. Heres a piece of code which does the job: (You can change the ImageView to any other thing and use it as an overlay.)

startPowerOverlay() function:

@SuppressLint("ClickableViewAccessibility")
    private void startPowerOverlay(){
        // Starts the button overlay.
        windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
        overlayPowerBtn = new ImageView(this);
        overlayPowerBtn.setImageResource(R.drawable.REPLACE_ME);

        int LAYOUT_FLAG;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            // APPLICATION_OVERLAY FOR ANDROID 26+ AS THE PREVIOUS VERSION RAISES ERRORS
            LAYOUT_FLAG = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
        } else {
            // FOR PREVIOUS VERSIONS USE TYPE_PHONE AS THE NEW VERSION IS NOT SUPPORTED
            LAYOUT_FLAG = WindowManager.LayoutParams.TYPE_PHONE;
        }

        WindowManager.LayoutParams params = new WindowManager.LayoutParams(
                WindowManager.LayoutParams.WRAP_CONTENT,
                WindowManager.LayoutParams.WRAP_CONTENT,
                LAYOUT_FLAG,
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
                PixelFormat.TRANSLUCENT);

        params.gravity = Gravity.TOP | Gravity.START;
        params.x = 0;
        params.y = 100;
        params.height = 110;
        params.width = 110;

        windowManager.addView(overlayPowerBtn, params);

        overlayPowerBtn.setOnTouchListener(new View.OnTouchListener() {
            private int initialX;
            private int initialY;
            private float initialTouchX;
            private float initialTouchY;
            private long latestPressTime = 0;

            @Override public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        // Save current x/y
                        initialX = params.x;
                        initialY = params.y;
                        initialTouchX = event.getRawX();
                        initialTouchY = event.getRawY();
                        // Check for double clicks. 
                        if (latestPressTime == 0 || latestPressTime + 500 < System.currentTimeMillis()) {
                            latestPressTime = System.currentTimeMillis();
                        } else {
                            // Doubleclicked. Do any action you'd like
                        }
                        return true;
                    case MotionEvent.ACTION_UP:
                        return true;
                    case MotionEvent.ACTION_MOVE:
                        params.x = initialX + (int) (event.getRawX() - initialTouchX);
                        params.y = initialY + (int) (event.getRawY() - initialTouchY);
                        windowManager.updateViewLayout(overlayPowerBtn, params);
                        return true;
                }
                return false;
            }
        });
    }

on onCreate():

        // Check for overlay permission. If not enabled, request for it. If enabled, show the overlay
        if(Build.VERSION.SDK_INT >= 23 && !Settings.canDrawOverlays(context)){
            CharSequence text = "Please grant the access to the application.";
            int duration = Toast.LENGTH_SHORT;
            Toast toast = Toast.makeText(context, text, duration);
            toast.show();
            startActivity(new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION, Uri.fromParts("package", getPackageName(), null)));
        } else {
            startPowerOverlay();
        }

on onDestroy():

        if (overlayPowerBtn != null)
            windowManager.removeView(overlayPowerBtn);

Hope it helps.