Flutter WebView example code

AppDelegate.h

@interface AppDelegate : FlutterAppDelegate

@property (nonatomic, strong) FlutterViewController *rootViewController;
@property (nonatomic, strong) NSMutableArray *flutterViewControllers;

@end

AppDelegate.m

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application
    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    [GeneratedPluginRegistrant registerWithRegistry:self];
    self.rootViewController = (FlutterViewController*) self.window.rootViewController;

    UIButton* button = [[UIButton alloc] initWithFrame:CGRectMake(200, 100, 200, 80)];
    [button setTitle:@"OPEN" forState:UIControlStateNormal];
    [button setBackgroundColor:[UIColor redColor]];
    [button addTarget:self action:@selector(launchNewFlutterViewController) forControlEvents:UIControlEventTouchUpInside];
    [[self.rootViewController view] addSubview:button];

    return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

- (void)initFlutterViewControllers {
    _flutterViewControllers = [NSMutableArray array];
    for (int i = 0; i < 2; i++) {
        FlutterViewController* flutterViewController = [[FlutterViewController alloc] init];
        [GeneratedPluginRegistrant registerWithRegistry:flutterViewController.pluginRegistry];
        [flutterViewController setSplashScreenView:nil];
        [_flutterViewControllers addObject:flutterViewController];
    }
}

- (void)launchNewFlutterViewController {
    [self initFlutterViewControllers];

    // _flutterViewControllers[0] = Not working
    // _flutterViewControllers[1] = Working (last FVC with FlutterPlatformViewController instantiated)

    [self.rootViewController presentViewController:_flutterViewControllers[1]
                                          animated:YES
                                        completion:nil];
}

@end

main.dart

import 'dart:ui';

import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final size = window.physicalSize;
    final devicePixelRatio = window.devicePixelRatio;
    final double screenWidth = size.width / devicePixelRatio;
    final double screenHeight = size.height / devicePixelRatio;
    return MaterialApp(
      title: 'WebView Test',
      home: Scaffold(
        appBar: AppBar(
          title: Text('WebView Test'),
        ),
        body: Center(
          child: SingleChildScrollView(
            child: SizedBox.fromSize(
              size: Size(screenWidth * .9, screenHeight * .6),
              child: Container(
                decoration: BoxDecoration(border: Border.all(color: Colors.blue)),
                child: WebView(
                  initialUrl: 'https://flutter.dev',
                  javascriptMode: JavascriptMode.unrestricted,
                  gestureRecognizers: {}..add(Factory<VerticalDragGestureRecognizer>(() => VerticalDragGestureRecognizer())),
                ),
              ),
            ),
          ),
        ),
      ),
    );
  }
}