Transparent Navigation in Flutter on Android.

MainActivity.java

import android.graphics.Color;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.view.Window;

import io.flutter.app.FlutterActivity;
import io.flutter.plugins.GeneratedPluginRegistrant;


public class MainActivity extends FlutterActivity
{
	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		GeneratedPluginRegistrant.registerWith(this);
		drawUnderSystemUi();
	}

	@Override
	protected void onPostResume()
	{
		super.onPostResume();
		drawUnderSystemUi();
	}


	private void drawUnderSystemUi()
	{
		if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP){
			Window window = getWindow();
			int color;
			if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.O){
				color = Color.TRANSPARENT;
			}
			else{
				color = 0x22000000;
			}
			window.setNavigationBarColor(color);
			window.getDecorView().setSystemUiVisibility(
				View.SYSTEM_UI_FLAG_LAYOUT_STABLE |
				View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN |
				View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION);
		}
	}
}

your_app.dart

import 'dart:ui' as ui;
import 'package:flutter/foundation.dart' show defaultTargetPlatform;
import 'package:flutter/material.dart';

class YourApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: 'Your app',
        theme: ThemeData.dark(),
        builder: _supportTransparentNavOnAndroid,
        home: HomeScreen(),
    );
  }

  Widget _supportTransparentNavOnAndroid(BuildContext context, Widget child) {
    if (defaultTargetPlatform == TargetPlatform.android) {
      final mediaQuery = MediaQueryData.fromWindow(ui.window);
      final bottomInset = mediaQuery.viewInsets.bottom;
      return MediaQuery(
        data: mediaQuery.copyWith(
          padding: mediaQuery.padding.copyWith(
            bottom: (bottomInset < 64.0 ? bottomInset : 0.0),
          ),
          viewInsets: mediaQuery.viewInsets.copyWith(
            bottom: (bottomInset < 64.0 ? 0.0 : bottomInset),
          ),
        ),
        child: child,
      );
    } else {
      return child;
    }
  }
}