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amirhamirh
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[webview_flutter]Allow specifying a navigation delegate(Android and Dart). (#1236)
This allows the app to prevent specific navigations(e.g prevent navigating to specific URLs). flutter/flutter#25329 iOS implementation in #1323
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‎packages/webview_flutter/CHANGELOG.md

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## 0.3.4
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* Support specifying navigation delegates that can prevent navigations from being executed.
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## 0.3.3+2
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* Exclude LongPress handler from semantics tree since it does nothing.

‎packages/webview_flutter/android/build.gradle

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@@ -44,4 +44,8 @@ android {
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lintOptions {
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disable 'InvalidPackage'
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}
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dependencies {
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implementation 'androidx.webkit:webkit:1.0.0'
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}
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}

‎packages/webview_flutter/android/src/main/java/io/flutter/plugins/webviewflutter/FlutterWebView.java

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package io.flutter.plugins.webviewflutter;
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import android.annotation.TargetApi;
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import android.content.Context;
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import android.os.Build;
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import android.view.View;
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import android.webkit.WebStorage;
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import android.webkit.WebView;
@@ -21,6 +23,7 @@ public class FlutterWebView implements PlatformView, MethodCallHandler {
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private static final String JS_CHANNEL_NAMES_FIELD = "javascriptChannelNames";
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private final WebView webView;
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private final MethodChannel methodChannel;
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private final FlutterWebViewClient flutterWebViewClient;
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@SuppressWarnings("unchecked")
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FlutterWebView(Context context, BinaryMessenger messenger, int id, Map<String, Object> params) {
@@ -31,12 +34,15 @@ public class FlutterWebView implements PlatformView, MethodCallHandler {
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methodChannel = new MethodChannel(messenger, "plugins.flutter.io/webview_" + id);
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methodChannel.setMethodCallHandler(this);
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flutterWebViewClient = new FlutterWebViewClient(methodChannel);
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applySettings((Map<String, Object>) params.get("settings"));
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if (params.containsKey(JS_CHANNEL_NAMES_FIELD)) {
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registerJavaScriptChannelNames((List<String>) params.get(JS_CHANNEL_NAMES_FIELD));
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}
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webView.setWebViewClient(flutterWebViewClient);
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if (params.containsKey("initialUrl")) {
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String url = (String) params.get("initialUrl");
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webView.loadUrl(url);
@@ -135,6 +141,7 @@ private void updateSettings(MethodCall methodCall, Result result) {
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result.success(null);
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}
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@TargetApi(Build.VERSION_CODES.KITKAT)
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private void evaluateJavaScript(MethodCall methodCall, final Result result) {
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String jsString = (String) methodCall.arguments;
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if (jsString == null) {
@@ -178,6 +185,9 @@ private void applySettings(Map<String, Object> settings) {
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case "jsMode":
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updateJsMode((Integer) settings.get(key));
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break;
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case "hasNavigationDelegate":
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flutterWebViewClient.setHasNavigationDelegate((boolean) settings.get(key));
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break;
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default:
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throw new IllegalArgumentException("Unknown WebView setting: " + key);
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}

‎packages/webview_flutter/android/src/main/java/io/flutter/plugins/webviewflutter/FlutterWebViewClient.java

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// Copyright 2019 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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package io.flutter.plugins.webviewflutter;
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import android.annotation.TargetApi;
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import android.os.Build;
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import android.util.Log;
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import android.webkit.WebResourceRequest;
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import android.webkit.WebView;
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import androidx.webkit.WebViewClientCompat;
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import io.flutter.plugin.common.MethodChannel;
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import java.util.HashMap;
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import java.util.Map;
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// We need to use WebViewClientCompat to get
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// shouldOverrideUrlLoading(WebView view, WebResourceRequest request)
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// invoked by the webview on older Android devices, without it pages that use iframes will
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// be broken when a navigationDelegate is set on Android version earlier than N.
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class FlutterWebViewClient extends WebViewClientCompat {
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private static final String TAG = "FlutterWebViewClient";
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private final MethodChannel methodChannel;
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private boolean hasNavigationDelegate;
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FlutterWebViewClient(MethodChannel methodChannel) {
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this.methodChannel = methodChannel;
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}
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void setHasNavigationDelegate(boolean hasNavigationDelegate) {
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this.hasNavigationDelegate = hasNavigationDelegate;
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}
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@TargetApi(Build.VERSION_CODES.LOLLIPOP)
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@Override
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public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
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if (!hasNavigationDelegate) {
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return false;
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}
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notifyOnNavigationRequest(
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request.getUrl().toString(), request.getRequestHeaders(), view, request.isForMainFrame());
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// We must make a synchronous decision here whether to allow the navigation or not,
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// if the Dart code has set a navigation delegate we want that delegate to decide whether
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// to navigate or not, and as we cannot get a response from the Dart delegate synchronously we
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// return true here to block the navigation, if the Dart delegate decides to allow the
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// navigation the plugin will later make an addition loadUrl call for this url.
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//
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// Since we cannot call loadUrl for a subframe, we currently only allow the delegate to stop
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// navigations that target the main frame, if the request is not for the main frame
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// we just return false to allow the navigation.
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//
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// For more details see: https://github.com/flutter/flutter/issues/25329#issuecomment-464863209
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return request.isForMainFrame();
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}
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@Override
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public boolean shouldOverrideUrlLoading(WebView view, String url) {
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if (!hasNavigationDelegate) {
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return false;
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}
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// This version of shouldOverrideUrlLoading is only invoked by the webview on devices with
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// webview versions earlier than 67(it is also invoked when hasNavigationDelegate is false).
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// On these devices we cannot tell whether the navigation is targeted to the main frame or not.
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// We proceed assuming that the navigation is targeted to the main frame. If the page had any
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// frames they will be loaded in the main frame instead.
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Log.w(
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TAG,
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"Using a navigationDelegate with an old webview implementation, pages with frames or iframes will not work");
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notifyOnNavigationRequest(url, null, view, true);
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return true;
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}
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private void notifyOnNavigationRequest(
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String url, Map<String, String> headers, WebView webview, boolean isMainFrame) {
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HashMap<String, Object> args = new HashMap<>();
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args.put("url", url);
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args.put("isForMainFrame", isMainFrame);
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if (isMainFrame) {
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methodChannel.invokeMethod(
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"navigationRequest", args, new OnNavigationRequestResult(url, headers, webview));
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} else {
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methodChannel.invokeMethod("navigationRequest", args);
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}
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}
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private static class OnNavigationRequestResult implements MethodChannel.Result {
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private final String url;
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private final Map<String, String> headers;
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private final WebView webView;
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private OnNavigationRequestResult(String url, Map<String, String> headers, WebView webView) {
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this.url = url;
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this.headers = headers;
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this.webView = webView;
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}
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@Override
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public void success(Object shouldLoad) {
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Boolean typedShouldLoad = (Boolean) shouldLoad;
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if (typedShouldLoad) {
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loadUrl();
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}
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}
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@Override
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public void error(String errorCode, String s1, Object o) {
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throw new IllegalStateException("navigationRequest calls must succeed");
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}
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@Override
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public void notImplemented() {
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throw new IllegalStateException(
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"navigationRequest must be implemented by the webview method channel");
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}
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private void loadUrl() {
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if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
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webView.loadUrl(url, headers);
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} else {
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webView.loadUrl(url);
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}
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}
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}
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}

‎packages/webview_flutter/example/android/gradle.properties

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org.gradle.jvmargs=-Xmx1536M
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android.useAndroidX=true

‎packages/webview_flutter/example/lib/main.dart

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// found in the LICENSE file.
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import 'dart:async';
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import 'dart:convert';
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import 'package:flutter/material.dart';
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import 'package:webview_flutter/webview_flutter.dart';
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void main() => runApp(MaterialApp(home: WebViewExample()));
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const String kNavigationExamplePage = '''
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<!DOCTYPE html><html>
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<head><title>Navigation Delegate Example</title></head>
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<body>
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<p>
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The navigation delegate is set to block navigation to the youtube website.
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</p>
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<ul>
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<ul><a href="https://www.youtube.com/">https://www.youtube.com/</a></ul>
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<ul><a href="https://www.google.com/">https://www.google.com/</a></ul>
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</ul>
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</body>
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</html>
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''';
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class WebViewExample extends StatelessWidget {
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final Completer<WebViewController> _controller =
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Completer<WebViewController>();
@@ -37,6 +53,14 @@ class WebViewExample extends StatelessWidget {
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javascriptChannels: <JavascriptChannel>[
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_toasterJavascriptChannel(context),
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].toSet(),
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navigationDelegate: (NavigationRequest request) {
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if (request.url.startsWith('https://www.youtube.com/')) {
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print('blocking navigation to $request}');
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return NavigationDecision.prevent;
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}
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print('allowing navigation to $request');
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return NavigationDecision.navigate;
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},
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);
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}),
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floatingActionButton: favoriteButton(),
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enum MenuOptions {
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showUserAgent,
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toast,
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listCookies,
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clearCookies,
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addToCache,
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listCache,
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clearCache,
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navigationDelegate,
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}
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class SampleMenu extends StatelessWidget {
@@ -102,13 +126,6 @@ class SampleMenu extends StatelessWidget {
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case MenuOptions.showUserAgent:
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_onShowUserAgent(controller.data, context);
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break;
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case MenuOptions.toast:
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Scaffold.of(context).showSnackBar(
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SnackBar(
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content: Text('You selected: $value'),
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),
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);
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break;
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case MenuOptions.listCookies:
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_onListCookies(controller.data, context);
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break;
@@ -124,6 +141,9 @@ class SampleMenu extends StatelessWidget {
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case MenuOptions.clearCache:
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_onClearCache(controller.data, context);
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break;
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case MenuOptions.navigationDelegate:
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_onNavigationDelegateExample(controller.data, context);
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break;
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}
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},
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itemBuilder: (BuildContext context) => <PopupMenuItem<MenuOptions>>[
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child: const Text('Show user agent'),
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enabled: controller.hasData,
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),
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const PopupMenuItem<MenuOptions>(
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value: MenuOptions.toast,
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child: Text('Make a toast'),
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),
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const PopupMenuItem<MenuOptions>(
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value: MenuOptions.listCookies,
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child: Text('List cookies'),
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value: MenuOptions.clearCache,
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child: Text('Clear cache'),
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),
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const PopupMenuItem<MenuOptions>(
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value: MenuOptions.navigationDelegate,
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child: Text('Navigation Delegate example'),
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),
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],
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);
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},
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));
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}
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241+
void _onNavigationDelegateExample(
242+
WebViewController controller, BuildContext context) async {
243+
final String contentBase64 =
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base64Encode(const Utf8Encoder().convert(kNavigationExamplePage));
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controller.loadUrl('data:text/html;base64,$contentBase64');
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}
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Widget _getCookieList(String cookies) {
222249
if (cookies == null || cookies == '""') {
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return Container();

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