[webview_flutter_lwe] Fix navigation delegate callbacks after delegate replacement

When the navigation delegate is replaced after the WebView is created, the new
delegate's platform channel handler was never registered because it is only set
up when the view is first created. As a result the new delegate's callbacks
(onUrlChange, onPageFinished, onProgress, etc.) were still delivered to the
previous delegate and silently dropped.

Bind the new delegate's channel handler when the delegate is set after the view
has been created, and guard the handler setup so a delegate is bound at most
once. This makes onUrlChange work when a delegate is swapped, which the
'can receive url changes' integration test exercises.

Author: seungsoo47

packages/webview_flutter_lwe/CHANGELOG.md

@@ -1,6 +1,8 @@
 ## 0.4.2
 
 * Implement `onUrlChange` for the navigation delegate.
+* Fix navigation delegate callbacks being dropped when the navigation delegate
+  is replaced after the WebView is created.
 * Add 1 integration test case.
 
 ## 0.4.1

packages/webview_flutter_lwe/lib/src/lwe_webview_controller.dart

@@ -25,9 +25,11 @@ class LweWebViewController extends PlatformWebViewController {
 
   final LweWebView _webview;
   late LweNavigationDelegate _lweNavigationDelegate;
+  int? _viewId;
 
   /// Called when [TizenView] is created.
   void onCreate(int viewId) {
+    _viewId = viewId;
     if (_webview.hasNavigationDelegate) {
       _lweNavigationDelegate.onCreate(viewId);
     }
@@ -142,6 +144,15 @@ class LweWebViewController extends PlatformWebViewController {
   ) async {
     _lweNavigationDelegate = handler;
     _webview.hasNavigationDelegate = true;
+    // If the view has already been created, the previous delegate's method
+    // call handler is the one currently bound to the platform channel. Bind
+    // the new delegate now so its callbacks (e.g. onUrlChange, onPageFinished)
+    // are the ones invoked; otherwise events would keep going to the old
+    // delegate and be dropped.
+    final int? viewId = _viewId;
+    if (viewId != null) {
+      handler.onCreate(viewId);
+    }
   }
 
   @override
@@ -383,6 +394,7 @@ class LweNavigationDelegate extends PlatformNavigationDelegate {
   LweNavigationDelegate(super.params) : super.implementation();
 
   late final MethodChannel _navigationDelegateChannel;
+  bool _isChannelCreated = false;
   PageEventCallback? _onPageFinished;
   PageEventCallback? _onPageStarted;
   ProgressCallback? _onProgress;
@@ -392,6 +404,13 @@ class LweNavigationDelegate extends PlatformNavigationDelegate {
 
   /// Called when [TizenView] is created.
   void onCreate(int viewId) {
+    // Guard against being bound twice for the same delegate instance; the
+    // channel handler below always reads the latest callbacks, so re-binding
+    // is unnecessary.
+    if (_isChannelCreated) {
+      return;
+    }
+    _isChannelCreated = true;
     _navigationDelegateChannel = MethodChannel(
       kLweNavigationDelegateChannelName + viewId.toString(),
     );