[webview_flutter]Allow specifying a navigation delegate(Android and Dart).

packages/webview_flutter/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.3.4
+
+* Support specifying navigation delegates that can prevent navigations from being executed.
+
 ## 0.3.3+2
 
 * Exclude LongPress handler from semantics tree since it does nothing.

packages/webview_flutter/android/build.gradle

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

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

@@ -4,7 +4,9 @@
 
 package io.flutter.plugins.webviewflutter;
 
+import android.annotation.TargetApi;
 import android.content.Context;
+import android.os.Build;
 import android.view.View;
 import android.webkit.WebStorage;
 import android.webkit.WebView;
@@ -21,6 +23,7 @@ public class FlutterWebView implements PlatformView, MethodCallHandler {
  private static final String JS_CHANNEL_NAMES_FIELD = "javascriptChannelNames";
  private final WebView webView;
  private final MethodChannel methodChannel;
+ private final FlutterWebViewClient flutterWebViewClient;
 
  @SuppressWarnings("unchecked")
  FlutterWebView(Context context, BinaryMessenger messenger, int id, Map<String, Object> params) {
@@ -31,12 +34,15 @@ public class FlutterWebView implements PlatformView, MethodCallHandler {
  methodChannel = new MethodChannel(messenger, "plugins.flutter.io/webview_" + id);
  methodChannel.setMethodCallHandler(this);
 
+ flutterWebViewClient = new FlutterWebViewClient(methodChannel);
  applySettings((Map<String, Object>) params.get("settings"));
 
  if (params.containsKey(JS_CHANNEL_NAMES_FIELD)) {
  registerJavaScriptChannelNames((List<String>) params.get(JS_CHANNEL_NAMES_FIELD));
  }
 
+ webView.setWebViewClient(flutterWebViewClient);
+
  if (params.containsKey("initialUrl")) {
  String url = (String) params.get("initialUrl");
  webView.loadUrl(url);
@@ -135,6 +141,7 @@ private void updateSettings(MethodCall methodCall, Result result) {
  result.success(null);
  }
 
+ @TargetApi(Build.VERSION_CODES.KITKAT)
  private void evaluateJavaScript(MethodCall methodCall, final Result result) {
  String jsString = (String) methodCall.arguments;
  if (jsString == null) {
@@ -178,6 +185,9 @@ private void applySettings(Map<String, Object> settings) {
  case "jsMode":
  updateJsMode((Integer) settings.get(key));
  break;
+ case "hasNavigationDelegate":
+ flutterWebViewClient.setHasNavigationDelegate((boolean) settings.get(key));
+ break;
  default:
  throw new IllegalArgumentException("Unknown WebView setting: " + key);
  }

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

@@ -0,0 +1,124 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package io.flutter.plugins.webviewflutter;
+
+import android.annotation.TargetApi;
+import android.os.Build;
+import android.util.Log;
+import android.webkit.WebResourceRequest;
+import android.webkit.WebView;
+import androidx.webkit.WebViewClientCompat;
+import io.flutter.plugin.common.MethodChannel;
+import java.util.HashMap;
+import java.util.Map;
+
+// We need to use WebViewClientCompat to get
+// shouldOverrideUrlLoading(WebView view, WebResourceRequest request)
+// invoked by the webview on older Android devices, without it pages that use iframes will
+// be broken when a navigationDelegate is set on Android version earlier than N.
+class FlutterWebViewClient extends WebViewClientCompat {
+ private static final String TAG = "FlutterWebViewClient";
+ private final MethodChannel methodChannel;
+ private boolean hasNavigationDelegate;
+
+ FlutterWebViewClient(MethodChannel methodChannel) {
+ this.methodChannel = methodChannel;
+ }
+
+ void setHasNavigationDelegate(boolean hasNavigationDelegate) {
+ this.hasNavigationDelegate = hasNavigationDelegate;
+ }
+
+ @TargetApi(Build.VERSION_CODES.LOLLIPOP)
+ @Override
+ public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
+ if (!hasNavigationDelegate) {
+ return false;
+ }
+ notifyOnNavigationRequest(
+ request.getUrl().toString(), request.getRequestHeaders(), view, request.isForMainFrame());
+ // We must make a synchronous decision here whether to allow the navigation or not,
+ // if the Dart code has set a navigation delegate we want that delegate to decide whether
+ // to navigate or not, and as we cannot get a response from the Dart delegate synchronously we
+ // return true here to block the navigation, if the Dart delegate decides to allow the
+ // navigation the plugin will later make an addition loadUrl call for this url.
+ //
+ // Since we cannot call loadUrl for a subframe, we currently only allow the delegate to stop
+ // navigations that target the main frame, if the request is not for the main frame
+ // we just return false to allow the navigation.
+ //
+ // For more details see: https://github.com/flutter/flutter/issues/25329#issuecomment-464863209
+ return request.isForMainFrame();
+ }
+
+ @Override
+ public boolean shouldOverrideUrlLoading(WebView view, String url) {
+ if (!hasNavigationDelegate) {
+ return false;
+ }
+ // This version of shouldOverrideUrlLoading is only invoked by the webview on devices with
+ // webview versions earlier than 67(it is also invoked when hasNavigationDelegate is false).
+ // On these devices we cannot tell whether the navigation is targeted to the main frame or not.
+ // We proceed assuming that the navigation is targeted to the main frame. If the page had any
+ // frames they will be loaded in the main frame instead.
+ Log.w(
+ TAG,
+ "Using a navigationDelegate with an old webview implementation, pages with frames or iframes will not work");
+ notifyOnNavigationRequest(url, null, view, true);
+ return true;
+ }
+
+ private void notifyOnNavigationRequest(
+ String url, Map<String, String> headers, WebView webview, boolean isMainFrame) {
+ HashMap<String, Object> args = new HashMap<>();
+ args.put("url", url);
+ args.put("isForMainFrame", isMainFrame);
+ if (isMainFrame) {
+ methodChannel.invokeMethod(
+ "navigationRequest", args, new OnNavigationRequestResult(url, headers, webview));
+ } else {
+ methodChannel.invokeMethod("navigationRequest", args);
+ }
+ }
+
+ private static class OnNavigationRequestResult implements MethodChannel.Result {
+ private final String url;
+ private final Map<String, String> headers;
+ private final WebView webView;
+
+ private OnNavigationRequestResult(String url, Map<String, String> headers, WebView webView) {
+ this.url = url;
+ this.headers = headers;
+ this.webView = webView;
+ }
+
+ @Override
+ public void success(Object shouldLoad) {
+ Boolean typedShouldLoad = (Boolean) shouldLoad;
+ if (typedShouldLoad) {
+ loadUrl();
+ }
+ }
+
+ @Override
+ public void error(String errorCode, String s1, Object o) {
+ throw new IllegalStateException("navigationRequest calls must succeed");
+ }
+
+ @Override
+ public void notImplemented() {
+ throw new IllegalStateException(
+ "navigationRequest must be implemented by the webview method channel");
+ }
+
+ private void loadUrl() {
+ if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+ webView.loadUrl(url, headers);
+ } else {
+ webView.loadUrl(url);
+ }
+ }
+ }
+}

packages/webview_flutter/example/android/gradle.properties

@@ -1 +1,2 @@
 org.gradle.jvmargs=-Xmx1536M
+android.useAndroidX=true

packages/webview_flutter/example/lib/main.dart

@@ -3,11 +3,27 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:convert';
 import 'package:flutter/material.dart';
 import 'package:webview_flutter/webview_flutter.dart';
 
 void main() => runApp(MaterialApp(home: WebViewExample()));
 
+const String kNavigationExamplePage = '''
+<!DOCTYPE html><html>
+<head><title>Navigation Delegate Example</title></head>
+<body>
+<p>
+The navigation delegate is set to block navigation to the youtube website.
+</p>
+<ul>
+<ul><a href="https://www.youtube.com/">https://www.youtube.com/</a></ul>
+<ul><a href="https://www.google.com/">https://www.google.com/</a></ul>
+</ul>
+</body>
+</html>
+''';
+
 class WebViewExample extends StatelessWidget {
  final Completer<WebViewController> _controller =
  Completer<WebViewController>();
@@ -37,6 +53,14 @@ class WebViewExample extends StatelessWidget {
  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;
+ },
  );
  }),
  floatingActionButton: favoriteButton(),
@@ -76,12 +100,12 @@ class WebViewExample extends StatelessWidget {
 
 enum MenuOptions {
  showUserAgent,
- toast,
  listCookies,
  clearCookies,
  addToCache,
  listCache,
  clearCache,
+ navigationDelegate,
 }
 
 class SampleMenu extends StatelessWidget {
@@ -102,13 +126,6 @@ class SampleMenu extends StatelessWidget {
  case MenuOptions.showUserAgent:
  _onShowUserAgent(controller.data, context);
  break;
- case MenuOptions.toast:
- Scaffold.of(context).showSnackBar(
- SnackBar(
- content: Text('You selected: $value'),
- ),
- );
- break;
  case MenuOptions.listCookies:
  _onListCookies(controller.data, context);
  break;
@@ -124,6 +141,9 @@ class SampleMenu extends StatelessWidget {
  case MenuOptions.clearCache:
  _onClearCache(controller.data, context);
  break;
+ case MenuOptions.navigationDelegate:
+ _onNavigationDelegateExample(controller.data, context);
+ break;
  }
  },
  itemBuilder: (BuildContext context) => <PopupMenuItem<MenuOptions>>[
@@ -132,10 +152,6 @@ class SampleMenu extends StatelessWidget {
  child: const Text('Show user agent'),
  enabled: controller.hasData,
  ),
- const PopupMenuItem<MenuOptions>(
- value: MenuOptions.toast,
- child: Text('Make a toast'),
- ),
  const PopupMenuItem<MenuOptions>(
  value: MenuOptions.listCookies,
  child: Text('List cookies'),
@@ -156,6 +172,10 @@ class SampleMenu extends StatelessWidget {
  value: MenuOptions.clearCache,
  child: Text('Clear cache'),
  ),
+ const PopupMenuItem<MenuOptions>(
+ value: MenuOptions.navigationDelegate,
+ child: Text('Navigation Delegate example'),
+ ),
  ],
  );
  },
@@ -218,6 +238,13 @@ class SampleMenu extends StatelessWidget {
  ));
  }
 
+ void _onNavigationDelegateExample(
+ WebViewController controller, BuildContext context) async {
+ final String contentBase64 =
+ base64Encode(const Utf8Encoder().convert(kNavigationExamplePage));
+ controller.loadUrl('data:text/html;base64,$contentBase64');
+ }
+
  Widget _getCookieList(String cookies) {
  if (cookies == null || cookies == '""') {
  return Container();