second screen

web.dart

import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';
import 'dart:async';


class Web extends StatefulWidget {
  final String url,title;
  final bool isAppBarVisible;

  Web({Key key, this.url, this.title, this.isAppBarVisible}) : super(key: key);
  @override
  _WebState createState() => _WebState();
}

class _WebState extends State<Web> {
  Completer<WebViewController> _controller = Completer<WebViewController>();

  /// ----------------------------------------------
  ///           Linear Progression Indicator
  /// ----------------------------------------------
    Widget _lpi = PreferredSize(
      preferredSize: Size(double.infinity, 7),
        child: LinearProgressIndicator(
          backgroundColor: Colors.black,
          valueColor: AlwaysStoppedAnimation<Color>(Colors.yellow)
        ),
    );
      
  
  navigationControls({Future<WebViewController> webViewControllerFuture, Icon icon, bool goback}){
    navigate(BuildContext context, WebViewController controller, {bool goBack}) async {
      bool canGoForward = await controller.canGoForward();
      bool canGoBack = await controller.canGoBack();
      bool canNavigate = goBack ? canGoBack : canGoForward;

      if (canNavigate) {
        goBack ? controller.goBack() : controller.goForward();
      }
      else {
        if(!canGoBack && goback){
          Navigator.of(context).pop();
        }
        else if(!canGoForward){
          Scaffold.of(context).showSnackBar(
            SnackBar(content: Text("No forward history!", textAlign: TextAlign.center,))
          );
        }
      }
    }

    return FutureBuilder<WebViewController>(
      future: webViewControllerFuture,
      builder: (BuildContext context, AsyncSnapshot<WebViewController> snapshot) {
        final bool webViewReady = snapshot.connectionState == ConnectionState.done;
        final WebViewController controller = snapshot.data;
        return  IconButton(
          icon: icon,
          onPressed: webViewReady
            ? () => navigate(context, controller, goBack: goback)
            : null,
        );
      },
    );
      
  } 


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: (widget.isAppBarVisible == null)
        ? null
        : AppBar(
            title: Text(widget.title),
            centerTitle: true,
            leading: navigationControls(
              webViewControllerFuture: _controller.future,
              icon: const Icon(Icons.arrow_back_ios),
              goback: true,
            ),
            actions: <Widget>[
              navigationControls(
                webViewControllerFuture: _controller.future,
                icon: const Icon(Icons.arrow_forward_ios),
                goback: false,
              ),
            ],
            bottom: _lpi,
          ),
      body: WebView(
        initialUrl: widget.url,
        onWebViewCreated: (WebViewController webViewController) {
          _controller.complete(webViewController);
        },
        onPageFinished: (val){
          setState(() {
            _lpi = null;
          });
        },
      ),

    );
  }
}