use WebViewClientCompat, rename isMainFrame to isForMainFrame

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/FlutterWebViewClient.java

@@ -6,14 +6,20 @@
 
 import android.annotation.TargetApi;
 import android.os.Build;
+import android.util.Log;
 import android.webkit.WebResourceRequest;
 import android.webkit.WebView;
-import android.webkit.WebViewClient;
+import androidx.webkit.WebViewClientCompat;
 import io.flutter.plugin.common.MethodChannel;
 import java.util.HashMap;
 import java.util.Map;
 
-class FlutterWebViewClient extends WebViewClient {
+// 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;
 
@@ -40,7 +46,7 @@ public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request
     // 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 originated in the main frame, if the request is not for the main frame
+    // 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
@@ -52,6 +58,14 @@ public boolean shouldOverrideUrlLoading(WebView view, String url) {
     if (!hasNavigationDelegate) {
       return super.shouldOverrideUrlLoading(view, url);
     }
+    // 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;
   }
@@ -60,7 +74,7 @@ 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("isMainFrame", isMainFrame);
+    args.put("isForMainFrame", isMainFrame);
     if (isMainFrame) {
       methodChannel.invokeMethod(
           "navigationRequest", args, new OnNavigationRequestResult(url, headers, webview));

packages/webview_flutter/example/android/gradle.properties

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

packages/webview_flutter/lib/webview_flutter.dart

@@ -35,17 +35,17 @@ typedef void JavascriptMessageHandler(JavascriptMessage message);
 
 /// Information about a navigation action that is about to be executed.
 class NavigationRequest {
-  NavigationRequest._({this.url, this.isMainFrame});
+  NavigationRequest._({this.url, this.isForMainFrame});
 
   /// The URL that will be loaded if the navigation is executed.
   final String url;
 
-  /// Whether the navigation request originated from the main HTML frame.
-  final bool isMainFrame;
+  /// Whether the navigation request is to be loaded as the main frame.
+  final bool isForMainFrame;
 
   @override
   String toString() {
-    return '$runtimeType(url: $url, isMainFrame: $isMainFrame)';
+    return '$runtimeType(url: $url, isForMainFrame: $isForMainFrame)';
   }
 }
 
@@ -385,7 +385,7 @@ class WebViewController {
       case 'navigationRequest':
         final NavigationRequest request = NavigationRequest._(
           url: call.arguments['url'],
-          isMainFrame: call.arguments['isMainFrame'],
+          isForMainFrame: call.arguments['isForMainFrame'],
         );
 
         // _navigationDelegate can be null if the widget was rebuilt with no

packages/webview_flutter/test/webview_flutter_test.dart

@@ -619,9 +619,10 @@ void main() {
       expect(platformWebView.currentUrl, 'https://youtube.com');
       expect(navigationRequests.length, 1);
       expect(navigationRequests[0].url, 'https://www.google.com');
-      expect(navigationRequests[0].isMainFrame, true);
+      expect(navigationRequests[0].isForMainFrame, true);
 
       platformWebView.fakeNavigate('https://flutter.dev');
+      await tester.pump();
       expect(platformWebView.currentUrl, 'https://flutter.dev');
     });
   });
@@ -737,12 +738,16 @@ class FakePlatformWebView {
     final StandardMethodCodec codec = const StandardMethodCodec();
     final Map<String, dynamic> arguments = <String, dynamic>{
       'url': url,
-      'isMainFrame': true
+      'isForMainFrame': true
     };
     final ByteData data =
         codec.encodeMethodCall(MethodCall('navigationRequest', arguments));
-    BinaryMessages.handlePlatformMessage(
-        channel.name, data, (ByteData data) {});
+    BinaryMessages.handlePlatformMessage(channel.name, data, (ByteData data) {
+      final bool allow = codec.decodeEnvelope(data);
+      if (allow) {
+        _loadUrl(url);
+      }
+    });
   }
 
   void _loadUrl(String url) {