Flutter button should load new webview url

This may be a relatively simple question, but I'm new to Flutter, and I need to implement this today.

I have a Flutter app that looks like this...

There's a Flutter BottomNavigationBar and a Flutter Webview_Plugin

All I need help with is for a new url to load when the button Home or Language is pressed. But I'm having trouble entirely figuring out the Flutter paradigm.

My current code, if it helps:

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_webview_plugin/flutter_webview_plugin.dart';
import 'package:flutter_webview_plugin_example/home.dart';
import 'package:flutter_webview_plugin_example/settings.dart';

const kAndroidUserAgent =
    'Mozilla/5.0 (Linux; Android 6.0; Nexus 5 Build/MRA58N) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/62.0.3202.94 Mobile Safari/537.36';

String selectedUrl = 'http://google.com';

void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'MyApp',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      routes: {
        '/': (_) => const MyHomePage(title: 'MyApp'),
        '/widget': (_) => new WebviewScaffold(
              url: selectedUrl,
              appBar: new AppBar(
                title: const Text('Widget webview'),
              ),
              withZoom: true,
              withLocalStorage: true,
            )
      },
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  // Instance of WebView plugin
  final flutterWebviewPlugin = new FlutterWebviewPlugin();

  // On destroy stream
  StreamSubscription _onDestroy;

  // On urlChanged stream
  StreamSubscription<String> _onUrlChanged;

  // On urlChanged stream
  StreamSubscription<WebViewStateChanged> _onStateChanged;

  StreamSubscription<WebViewHttpError> _onHttpError;

  StreamSubscription<double> _onScrollYChanged;

  StreamSubscription<double> _onScrollXChanged;

  final _urlCtrl = new TextEditingController(text: selectedUrl);

  final _codeCtrl =
      new TextEditingController(text: 'window.navigator.userAgent');

  final _scaffoldKey = new GlobalKey<ScaffoldState>();

  final _history = [];

  @override
  void initState() {
    super.initState();

    flutterWebviewPlugin.close();

    SystemChrome.setEnabledSystemUIOverlays([SystemUiOverlay.bottom]);

    _urlCtrl.addListener(() {
      selectedUrl = _urlCtrl.text;
    });

    // Add a listener to on destroy WebView, so you can make came actions.
    _onDestroy = flutterWebviewPlugin.onDestroy.listen((_) {
      if (mounted) {
        // Actions like show a info toast.
        _scaffoldKey.currentState.showSnackBar(
            const SnackBar(content: const Text('Webview Destroyed')));
      }
    });

    // Add a listener to on url changed
    _onUrlChanged = flutterWebviewPlugin.onUrlChanged.listen((String url) {
      if (mounted) {
        setState(() {
          _history.add('onUrlChanged: $url');
        });
      }
    });

    _onScrollYChanged =
        flutterWebviewPlugin.onScrollYChanged.listen((double y) {
      if (mounted) {
        setState(() {
          _history.add("Scroll in Y Direction: $y");
        });
      }
    });

    _onScrollXChanged =
        flutterWebviewPlugin.onScrollXChanged.listen((double x) {
      if (mounted) {
        setState(() {
          _history.add("Scroll in X Direction: $x");
        });
      }
    });

    _onStateChanged =
        flutterWebviewPlugin.onStateChanged.listen((WebViewStateChanged state) {
      if (mounted) {
        setState(() {
          _history.add('onStateChanged: ${state.type} ${state.url}');
        });
      }
    });

    _onHttpError =
        flutterWebviewPlugin.onHttpError.listen((WebViewHttpError error) {
      if (mounted) {
        setState(() {
          _history.add('onHttpError: ${error.code} ${error.url}');
        });
      }
    });
  }

  @override
  void dispose() {
    // Every listener should be canceled, the same should be done with this stream.
    _onDestroy.cancel();
    _onUrlChanged.cancel();
    _onStateChanged.cancel();
    _onHttpError.cancel();
    _onScrollXChanged.cancel();
    _onScrollYChanged.cancel();

    flutterWebviewPlugin.dispose();

    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    BottomNavigationBar btm = new BottomNavigationBar(
      items: [
        new BottomNavigationBarItem(
            icon: new Icon(
              Icons.home,
              color: const Color(0xFFFFFFFF),
            ),
            title: new Text(
              "Home",
              style: new TextStyle(
                color: const Color(0xFFFFFFFF),
              ),
            )),
        new BottomNavigationBarItem(
            icon: new Icon(
              Icons.settings,
              color: const Color(0xFFFFFFFF),
            ),
            title: new Text(
              "Language",
              style: new TextStyle(
                color: const Color(0xFFFFFFFF),
              ),
            )),
      ],
//      onTap: changeURL()
    );

    flutterWebviewPlugin.launch(selectedUrl,
    rect: new Rect.fromLTWH(
    0.0, 0.0,
    MediaQuery.of(context).size.width, MediaQuery.of(context).size.height - 55),
    userAgent: kAndroidUserAgent);

    return new Scaffold(
      appBar: new AppBar(
        title: new Text(
          widget.title,
          style: new TextStyle(color: const Color(0xFFFFFFFF)),
        ),
      ),
      bottomNavigationBar: new Theme(
        data: Theme.of(context).copyWith(
          // sets the background color of the `BottomNavigationBar`
          canvasColor: const Color(0xFF167F67),
        ), // sets the inactive color of the `BottomNavigationBar`
        child: btm
      ),
    );
  }
}