Implement scroll listener for Android

Author: TheVinhLuong

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

@@ -0,0 +1,6 @@
+package io.flutter.plugins.webviewflutter;
+
+
+public interface OnScrollChangedCallback {
+    void onScroll(int l, int t, int oldl, int oldt);
+}

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

@@ -81,7 +81,7 @@ private void setUp(
 
     webViewHostApi =
         new WebViewHostApiImpl(
-            instanceManager, new WebViewHostApiImpl.WebViewProxy(), context, containerView);
+            instanceManager, new WebViewHostApiImpl.WebViewProxy(), context, containerView,new WebViewClientFlutterApiImpl(binaryMessenger, instanceManager));
     javaScriptChannelHostApi =
         new JavaScriptChannelHostApiImpl(
             instanceManager,

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

@@ -12,15 +12,17 @@
 import android.webkit.WebChromeClient;
 import android.webkit.WebView;
 import android.webkit.WebViewClient;
+
+import java.util.HashMap;
+import java.util.Map;
+
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import io.flutter.plugin.platform.PlatformView;
 import io.flutter.plugins.webviewflutter.DownloadListenerHostApiImpl.DownloadListenerImpl;
 import io.flutter.plugins.webviewflutter.GeneratedAndroidWebView.WebViewHostApi;
 import io.flutter.plugins.webviewflutter.WebChromeClientHostApiImpl.WebChromeClientImpl;
 import io.flutter.plugins.webviewflutter.WebViewClientHostApiImpl.ReleasableWebViewClient;
-import java.util.HashMap;
-import java.util.Map;
 
 /**
  * Host api implementation for {@link WebView}.
@@ -35,8 +37,10 @@ public class WebViewHostApiImpl implements WebViewHostApi {
 
   private final InstanceManager instanceManager;
   private final WebViewProxy webViewProxy;
+  private final WebViewClientFlutterApiImpl flutterApi;
   // Only used with WebView using virtual displays.
-  @Nullable private final View containerView;
+  @Nullable
+  private final View containerView;
 
   private Context context;
 
@@ -111,6 +115,7 @@ public static class WebViewPlatformView extends WebView implements PlatformView,
         new ReleasableValue<>();
     private final Map<String, ReleasableValue<JavaScriptChannel>> javaScriptInterfaces =
         new HashMap<>();
+    private OnScrollChangedCallback mOnScrollChangedCallback;
 
     /**
      * Creates a {@link WebViewPlatformView}.
@@ -185,6 +190,18 @@ public void release() {
       }
       javaScriptInterfaces.clear();
     }
+
+    @Override
+    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
+      super.onScrollChanged(l, t, oldl, oldt);
+      if (mOnScrollChangedCallback != null) {
+        mOnScrollChangedCallback.onScroll(l, t, oldl, oldt);
+      }
+    }
+
+    public void setOnScrollChangedCallback(final OnScrollChangedCallback onScrollChangedCallback) {
+      mOnScrollChangedCallback = onScrollChangedCallback;
+    }
   }
 
   /**
@@ -303,19 +320,21 @@ public void release() {
    * Creates a host API that handles creating {@link WebView}s and invoking its methods.
    *
    * @param instanceManager maintains instances stored to communicate with Dart objects
-   * @param webViewProxy handles creating {@link WebView}s and calling its static methods
-   * @param context an Activity Context to access application assets. This value cannot be null.
-   * @param containerView parent of the webView
+   * @param webViewProxy    handles creating {@link WebView}s and calling its static methods
+   * @param context         an Activity Context to access application assets. This value cannot be null.
+   * @param containerView   parent of the webView
    */
   public WebViewHostApiImpl(
-      InstanceManager instanceManager,
-      WebViewProxy webViewProxy,
-      Context context,
-      @Nullable View containerView) {
+          InstanceManager instanceManager,
+          WebViewProxy webViewProxy,
+          Context context,
+          @Nullable View containerView,
+          WebViewClientFlutterApiImpl flutterApi) {
     this.instanceManager = instanceManager;
     this.webViewProxy = webViewProxy;
     this.context = context;
     this.containerView = containerView;
+    this.flutterApi = flutterApi;
   }
 
   /**
@@ -508,6 +527,14 @@ public void setWebChromeClient(Long instanceId, Long clientInstanceId) {
     webView.setWebChromeClient((WebChromeClient) instanceManager.getInstance(clientInstanceId));
   }
 
+  @Override
+  public void enableListenForScrollPos(Long instanceId, Long webViewClientInstanceId, Boolean enable) {
+    final WebViewHostApiImpl.WebViewPlatformView webView = (WebViewHostApiImpl.WebViewPlatformView) instanceManager.getInstance(instanceId);
+    webView.setOnScrollChangedCallback((l, t, oldl, oldt) -> flutterApi.onScrollPosChange(webViewClientInstanceId,
+            instanceId,
+            (long) l, (long) t, reply -> {}));
+  }
+
   @Override
   public void setBackgroundColor(Long instanceId, Long color) {
     final WebView webView = (WebView) instanceManager.getInstance(instanceId);

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

@@ -117,6 +117,9 @@ class _WebViewExampleState extends State<_WebViewExample> {
           initialUrl: 'https://flutter.dev',
           onWebViewCreated: (WebViewController controller) {
             _controller.complete(controller);
+            controller.setOnScrollListener((int x, int y) {
+              print('New scroll position: x = $x, y = $y');
+            });
           },
           onProgress: (int progress) {
             print('WebView is loading (progress : $progress%)');

packages/webview_flutter/webview_flutter_android/example/lib/main.dart

@@ -40,6 +40,9 @@ typedef PageLoadingCallback = void Function(int progress);
 /// Signature for when a [WebView] has failed to load a resource.
 typedef WebResourceErrorCallback = void Function(WebResourceError error);
 
+/// Signature for when a [WebView] scroll position changed.
+typedef OnScrollPosChangeCallback = void Function(int x, int y);
+
 /// A web view widget for showing html content.
 ///
 /// The [WebView] widget wraps around the [AndroidWebView] or
@@ -195,7 +198,7 @@ class WebView extends StatefulWidget {
   ///
   /// This callback is only called for the main page.
   final WebResourceErrorCallback? onWebResourceError;
-
+  
   /// Controls whether WebView debugging is enabled.
   ///
   /// Setting this to true enables [WebView debugging on Android](https://developers.google.com/web/tools/chrome-devtools/remote-debugging/).
@@ -286,6 +289,7 @@ class _WebViewState extends State<WebView> {
           webViewPlatformController!,
           _javascriptChannelRegistry,
         );
+        _platformCallbacksHandler._webViewController = controller;
         _controller.complete(controller);
 
         if (widget.onWebViewCreated != null) {
@@ -310,9 +314,14 @@ class _WebViewState extends State<WebView> {
 
 class _PlatformCallbacksHandler implements WebViewPlatformCallbacksHandler {
   _PlatformCallbacksHandler(this._webView);
+  WebViewController? _webViewController;
 
   final WebView _webView;
 
+  set webViewController(WebViewController value) {
+    _webViewController = value;
+  }
+
   @override
   FutureOr<bool> onNavigationRequest({
     required String url,
@@ -347,6 +356,11 @@ class _PlatformCallbacksHandler implements WebViewPlatformCallbacksHandler {
     }
   }
 
+  @override
+  void onScrollPosChange(int x, int y) {
+    _webViewController?.onScrollPosChangeCallback?.call(x, y);
+  }
+
   @override
   void onWebResourceError(WebResourceError error) {
     if (_webView.onWebResourceError != null) {
@@ -374,6 +388,8 @@ class WebViewController {
 
   final WebViewPlatformController _webViewPlatformController;
 
+  OnScrollPosChangeCallback? onScrollPosChangeCallback;
+
   late WebSettings _settings;
 
   WebView _widget;
@@ -600,6 +616,12 @@ class WebViewController {
     return _webViewPlatformController.getScrollY();
   }
 
+  /// Set the scroll listener callback
+  Future<void> setOnScrollListener(OnScrollPosChangeCallback? callback) {
+    onScrollPosChangeCallback = callback;
+    return _webViewPlatformController.enableScrollListener(callback != null);
+  }
+
   // This method assumes that no fields in `currentValue` are null.
   WebSettings _clearUnchangedWebSettings(
       WebSettings currentValue, WebSettings newValue) {

packages/webview_flutter/webview_flutter_android/example/lib/web_view.dart

@@ -365,6 +365,12 @@ class WebView {
     return api.setBackgroundColorFromInstance(this, color.value);
   }
 
+  /// Enable scroll listener for this WebView.
+  Future<void> enableListenForScrollPos(bool enable) {
+    return api.enableListenForScrollPosFromInstance(
+        this, _currentWebViewClient!, enable);
+  }
+
   /// Releases all resources used by the [WebView].
   ///
   /// Any methods called after [release] will throw an exception.
@@ -745,6 +751,9 @@ abstract class WebViewClient {
   /// causes the current [WebView] to abort loading the URL, while returning
   /// false causes the [WebView] to continue loading the URL as usual.
   void urlLoading(WebView webView, String url) {}
+
+  /// Notify a new scroll position for the current [WebView]
+  void onScrollPosChange(WebView webView, int x, int y) {}
 }
 
 /// The interface to be used when content can not be handled by the rendering engine for [WebView], and should be downloaded instead.