[webview_flutter] onPageFinished never gets called on iOS with an invalid URL

[S4b3]

I'm working with webview_flutter in order to Auth my users through Cognito's auth endpoint.

This is my WebView:

    return WebView(
        initialUrl: url,
        userAgent: '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',
        javascriptMode: JavascriptMode.unrestricted,
        onWebViewCreated: (WebViewController webViewController) {
          _webViewController.complete(webViewController);
        },
        navigationDelegate: (NavigationRequest request) async {
          print("Current url : ${request.url}");
          if (request.url.startsWith('myapp://?code=')) {
            print("Preventing navigation");
            return NavigationDecision.prevent;
          }
          print("Navigated to url");
        },
        onPageFinished: (String url) async {
          print("onPageFinished with url: $url");
          if (url.startsWith('myapp://?code=')) {
            code = url.substring('myapp://?code='.length).split('#')[0];
            final Map<String, String> userData = await globals.cognitoClient
                .signUserInWithThirdPartyAuthCode(code);
            final UserModel user = await globals.appSyncClient.fetchMyProfile();
            userState.user = user;
            if (user.username != null && user.username != '') {
              Navigator.pushNamedAndRemoveUntil(
                  context, '/home', (Route<dynamic> route) => false);
            } else {
              Navigator.pushReplacement(context, MaterialPageRoute<dynamic>(
                builder: (BuildContext context) {
                  return TpSignUpPage(
                    name: userData['name'],
                    surname: userData['surname'],
                    tptype: widget.tpType,
                  );
                },
              ));
            }
          }
        },
        gestureNavigationEnabled: true,
      );

Preventing navigation when the url contains my auth code allows me to do the magic inside onPageFinished and on Android everything works fine.

On the other hand, on iOS the onPageFinished callback never gets called. The print never shows up in the console and the navigation stops at the auth code without nothing getting done. I've even checked if requests are for the main frame, they are.
This is what i get:

flutter: Current url : https://xxxxxxxxxxx.auth.eu-central-1.amazoncognito.com/oauth2/authorize?identity_provider=Facebook&redirect_uri=myapp://&response_type=CODE&client_id=xxxxxxxxxxxxxxxxxxxxxx&scope=email%20openid%20profile%20aws.cognito.signin.user.admin
flutter: Navigated to url
flutter: Current url : myapp://?code=4xxxxxxx-xxx8-xxxx-a88a-7xxxxxxxxx3
flutter: Preventing navigation

Whereas after every navigation onPageFinished's supposed to be called.
I really don't know how or why this might happen; I've searched through many issues and my current Info.plist contains :

    <key>io.flutter.embedded_views_preview</key>
    <true/>

and this is my flutter doctor -v:

[✓] Flutter (Channel stable, 1.22.5, on Mac OS X 10.15.7 19H2 darwin-x64, locale it-IT)
    • Flutter version 1.22.5 at /usr/local/Caskroom/flutter/1.22.0/flutter
    • Framework revision 7891006299 (7 weeks ago), 2020-12-10 11:54:40 -0800
    • Engine revision ae90085a84
    • Dart version 2.10.4

 
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/sabe/Library/Android/sdk
    • Platform android-30, build-tools 30.0.2
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.2)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.2, Build version 12B45b
    • CocoaPods version 1.9.3

[✓] Android Studio (version 4.0)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 50.0.1
    • Dart plugin version 193.7547
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

[!] IntelliJ IDEA Ultimate Edition (version 2019.1.3)
    • IntelliJ at /Applications/IntelliJ IDEA.app
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • For information about installing plugins, see
      https://flutter.dev/intellij-setup/#installing-the-plugins

[✓] VS Code (version 1.52.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.18.1

[✓] Connected device (1 available)
    • iPhone 12 Pro Max (mobile) • 83C45AD2-68CE-4260-B932-57C4B5B861D4 • ios •
      com.apple.CoreSimulator.SimRuntime.iOS-14-2 (simulator)

! Doctor found issues in 1 category.

(I don't use IntelliJ anymore so w/ever)

Steps to Reproduce : I'm assuming just run a webview on ios having onPageFinished populated ?
What could be causing this issue? Pls send help

[TahaTesser]

Hi @S4b3
Can you please provide` a complete reproducible minimal code sample
I tried to reproduce using the official example

flutter: Page finished loading: https://flutter.dev/
flutter: allowing navigation to NavigationRequest(url: https://flutter.dev/docs/testing/debugging, isForMainFrame: true)
flutter: Page started loading: https://flutter.dev/docs/testing/debugging
flutter: Page finished loading: https://flutter.dev/docs/testing/debugging

flutter doctor -v

[✓] Flutter (Channel stable, 1.22.6, on macOS 11.1 20C69 darwin-x64, locale en-GB)
    • Flutter version 1.22.6 at /Users/tahatesser/Code/flutter_stable
    • Framework revision 9b2d32b605 (9 days ago), 2021-01-22 14:36:39 -0800
    • Engine revision 2f0af37152
    • Dart version 2.10.5

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at /Volumes/Extreme/SDK
    • Platform android-30, build-tools 30.0.3
    • ANDROID_HOME = /Volumes/Extreme/SDK
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.4)
    • Xcode at /Volumes/Extreme/Xcode.app/Contents/Developer
    • Xcode 12.4, Build version 12D4e
    • CocoaPods version 1.10.1

[!] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.52.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.19.0

[!] Connected device
    ! No devices available

! Doctor found issues in 2 categories.

Thank you

[S4b3]

Sadly the official example doesn't cover my issue.
As for what I managed to understand during the past few days, having this as a webview:

return WebView(
       initialUrl: 'myapp://?code',
       userAgent: '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',
       javascriptMode: JavascriptMode.unrestricted,
       onWebViewCreated: (WebViewController webViewController) {
         _webViewController.complete(webViewController);
       },
       javascriptChannels: <JavascriptChannel>[
         _toasterJavascriptChannel(context),
       ].toSet(),
       navigationDelegate: (NavigationRequest request) {
         if (request.url.startsWith('https://www.youtube.com/')) {
           print('blocking navigation to $request}');
           return NavigationDecision.prevent;
         }
         print('allowing navigation to $request');
         return NavigationDecision.navigate;
       },
       onPageStarted: (String url) {
         print('Page started loading: $url');
       },
       onPageFinished: (String url) {
         print('Page finished loading: $url');
       },
       gestureNavigationEnabled: true,
     );
   }

Which only differs from the official example for the initialUrl, reproduces my problem.
Apparently Android's WebView manages to call the onPageFinished callback regardless if the Navigation was prevented or if the url hasn't led to an actual page; which to me sounds about right, since the page was infact loaded.

On iOS, instead, the method gets called way less (never, in this particular occasion) which ends up causing my problem.
For example, with the webview I quoted above this is the android console log:

I/flutter (14681): Page started loading: myapp://?code
I/flutter (14681): Page finished loading: myapp://?code

And this is iOS' :

flutter: allowing navigation to NavigationRequest(url: myapp://?code, isForMainFrame: true)
flutter: Page started loading: myapp://?code

Basically if loading the page would lead to an error or if the navigation was prevented the onPageFinished callback doesn't get called on iOS, which is a completely different behavior than android's and is causing me a massive headache.

Is there any way to manually handle this case?

[TahaTesser]

Hi @S4b3
Thanks for the details, I can reproduce the invalid initialUrl

With invalid URL on iOS

[  +44 ms] flutter: Page started loading: myapp://?code

With invalid URL on Android

[  +20 ms] I/flutter ( 9566): Page started loading: myapp://?code
[  +14 ms] I/flutter ( 9566): Page finished loading: myapp://?code

code sample

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Material App',
      theme: ThemeData.dark(),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final Completer<WebViewController> _webViewController =
      Completer<WebViewController>();

  final String _url = 'https://pub.dev';

  @override
  void initState() {
    super.initState();
    // Enable hybrid composition.
    if (Platform.isAndroid) WebView.platform = SurfaceAndroidWebView();
  }

  @override
  Widget build(BuildContext context) => Material(
        child: Center(
          child: WebView(
            initialUrl: 'myapp://?code',
            // initialUrl: _url,
            userAgent: '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',
            javascriptMode: JavascriptMode.unrestricted,
            onWebViewCreated: (WebViewController webViewController) {
              _webViewController.complete(webViewController);
            },
            javascriptChannels: <JavascriptChannel>[
              // _toasterJavascriptChannel(context),
            ].toSet(),
            navigationDelegate: (NavigationRequest request) {
              if (request.url.startsWith('https://www.youtube.com/')) {
                print('blocking navigation to $request}');
                return NavigationDecision.prevent;
              }
              print('allowing navigation to $request');
              return NavigationDecision.navigate;
            },
            onPageStarted: (String url) {
              print('Page started loading: $url');
            },
            onPageFinished: (String url) {
              print('Page finished loading: $url');
            },
            gestureNavigationEnabled: true,
          ),
        ),
      );
}

flutter doctor -v

[✓] Flutter (Channel stable, 1.22.6, on macOS 11.1 20C69 darwin-x64, locale en-GB)
    • Flutter version 1.22.6 at /Users/tahatesser/Code/flutter_stable
    • Framework revision 9b2d32b605 (10 days ago), 2021-01-22 14:36:39 -0800
    • Engine revision 2f0af37152
    • Dart version 2.10.5

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at /Volumes/Extreme/SDK
    • Platform android-30, build-tools 30.0.3
    • ANDROID_HOME = /Volumes/Extreme/SDK
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.4)
    • Xcode at /Volumes/Extreme/Xcode.app/Contents/Developer
    • Xcode 12.4, Build version 12D4e
    • CocoaPods version 1.10.1

[!] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.52.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.19.0

[✓] Connected device (2 available)
    • Android SDK built for x86 (mobile) • emulator-5554             • android-x86 • Android 10 (API 29) (emulator)
    • Taha’s iPad (mobile)               • 00008020-000255113EE8402E • ios         • iOS 14.4

! Doctor found issues in 1 category.

[✓] Flutter (Channel master, 1.26.0-18.0.pre.124, on macOS 11.1 20C69 darwin-x64, locale en-GB)
    • Flutter version 1.26.0-18.0.pre.124 at /Users/tahatesser/Code/flutter_master
    • Framework revision 0a4618943c (37 minutes ago), 2021-02-02 14:56:03 +0800
    • Engine revision bb2bbde4d0
    • Dart version 2.12.0 (build 2.12.0-279.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at /Volumes/Extreme/SDK
    • Platform android-30, build-tools 30.0.3
    • ANDROID_HOME = /Volumes/Extreme/SDK
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Volumes/Extreme/Xcode.app/Contents/Developer
    • Xcode 12.4, Build version 12D4e
    • CocoaPods version 1.10.1

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 4.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)

[✓] VS Code (version 1.52.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.19.0

[✓] Connected device (4 available)
    • Android SDK built for x86 (mobile) • emulator-5554             • android-x86    • Android 10 (API 29) (emulator)
    • Taha’s iPad (mobile)               • 00008020-000255113EE8402E • ios            • iOS 14.4
    • macOS (desktop)                    • macos                     • darwin-x64     • macOS 11.1 20C69 darwin-x64
    • Chrome (web)                       • chrome                    • web-javascript • Google Chrome 88.0.4324.96

• No issues found!

Thank you