Navigation bar filler for fullscreen layouts, to avoid elements falling behind nav bar on devices with soft navigation bar.

android_tricks_nav_bar_filler.md

In layout, align fab to be above empty layout.

   <android.support.constraint.ConstraintLayout
        android:id="@+id/nav_bar_filler"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:visibility="invisible"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"/>

In code, at onCreate -

    View nav_bar_filler = findViewById(R.id.nav_bar_filler);
		if (nav_bar_filler != null) {
			ViewGroup.MarginLayoutParams params = (ViewGroup.MarginLayoutParams) nav_bar_filler.getLayoutParams();
			params.bottomMargin = getNavigationBarSize(this).y;
		}

Add these helper methods too -

	public static Point getNavigationBarSize(Context context) {
		Point appUsableSize = getAppUsableScreenSize(context);
		Point realScreenSize = getRealScreenSize(context);

		// navigation bar on the right
		if (appUsableSize.x < realScreenSize.x) {
			return new Point(realScreenSize.x - appUsableSize.x, appUsableSize.y);
		}

		// navigation bar at the bottom
		if (appUsableSize.y < realScreenSize.y) {
			return new Point(appUsableSize.x, realScreenSize.y - appUsableSize.y);
		}

		// navigation bar is not present
		return new Point();
	}

	public static Point getAppUsableScreenSize(Context context) {
		WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
		Display display = windowManager.getDefaultDisplay();
		Point size = new Point();
		display.getSize(size);
		return size;
	}

	public static Point getRealScreenSize(Context context) {
		WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
		Display display = windowManager.getDefaultDisplay();
		Point size = new Point();

		if (Build.VERSION.SDK_INT >= 17) {
			display.getRealSize(size);
		} else if (Build.VERSION.SDK_INT >= 14) {
			try {
				size.x = (Integer) Display.class.getMethod("getRawWidth").invoke(display);
				size.y = (Integer) Display.class.getMethod("getRawHeight").invoke(display);
			} catch (IllegalAccessException e) {
			} catch (InvocationTargetException e) {
			} catch (NoSuchMethodException e) {
			}
		}

		return size;
	}