[webview_flutter] Add listener for scroll position change in Android

.gitignore

@@ -2,6 +2,7 @@
 .atom/
 .idea/
 .vscode/
+**/.fvm/
 
 .packages
 .pub/

packages/webview_flutter/webview_flutter/example/pubspec.yaml

@@ -38,3 +38,9 @@ flutter:
     - assets/sample_video.mp4
     - assets/www/index.html
     - assets/www/styles/style.css
+
+
+# FOR TESTING ONLY. DO NOT MERGE.
+dependency_overrides:
+  webview_flutter_platform_interface:
+    path: ../../../webview_flutter/webview_flutter_platform_interface

packages/webview_flutter/webview_flutter/pubspec.yaml

@@ -31,3 +31,9 @@ dev_dependencies:
     sdk: flutter
   mockito: ^5.3.2
   plugin_platform_interface: ^2.1.3
+
+
+# FOR TESTING ONLY. DO NOT MERGE.
+dependency_overrides:
+  webview_flutter_platform_interface:
+    path: ../../webview_flutter/webview_flutter_platform_interface

packages/webview_flutter/webview_flutter_android/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.3.1
+
+* Added `setOnContentOffsetChanged` method to the `AndroidWebViewController`.
+
 ## 3.3.0
 
 * Adds support to access native `WebView`.

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

@@ -0,0 +1,9 @@
+// Copyright 2013 The Flutter 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;
+
+public interface ContentOffsetChangedListener {
+  void onContentOffsetChange(int left, int top, int oldLeft, int oldTop);
+}

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

@@ -692,6 +692,8 @@ void removeJavaScriptChannel(
 
     void setBackgroundColor(@NonNull Long instanceId, @NonNull Long color);
 
+    void enableContentOffsetChangedListener(@NonNull Long instanceId, @NonNull Boolean enabled);
+
     /** The codec used by WebViewHostApi. */
     static MessageCodec<Object> getCodec() {
       return WebViewHostApiCodec.INSTANCE;
@@ -1558,6 +1560,40 @@ public void error(Throwable error) {
           channel.setMessageHandler(null);
         }
       }
+      {
+        BasicMessageChannel<Object> channel =
+            new BasicMessageChannel<>(
+                binaryMessenger,
+                "dev.flutter.pigeon.WebViewHostApi.enableContentOffsetChangedListener",
+                getCodec());
+        if (api != null) {
+          channel.setMessageHandler(
+              (message, reply) -> {
+                ArrayList wrapped = new ArrayList<>();
+                try {
+                  ArrayList<Object> args = (ArrayList<Object>) message;
+                  assert args != null;
+                  Number instanceIdArg = (Number) args.get(0);
+                  if (instanceIdArg == null) {
+                    throw new NullPointerException("instanceIdArg unexpectedly null.");
+                  }
+                  Boolean enabledArg = (Boolean) args.get(1);
+                  if (enabledArg == null) {
+                    throw new NullPointerException("enabledArg unexpectedly null.");
+                  }
+                  api.enableContentOffsetChangedListener(
+                      (instanceIdArg == null) ? null : instanceIdArg.longValue(), enabledArg);
+                  wrapped.add(0, null);
+                } catch (Error | RuntimeException exception) {
+                  ArrayList<Object> wrappedError = wrapError(exception);
+                  wrapped = wrappedError;
+                }
+                reply.reply(wrapped);
+              });
+        } else {
+          channel.setMessageHandler(null);
+        }
+      }
     }
   }
   /** Generated interface from Pigeon that represents a handler of messages from Flutter. */
@@ -2438,6 +2474,41 @@ public void onDownloadStart(
           });
     }
   }
+  /** Generated class from Pigeon that represents Flutter messages that can be called from Java. */
+  public static class WebViewFlutterApi {
+    private final BinaryMessenger binaryMessenger;
+
+    public WebViewFlutterApi(BinaryMessenger argBinaryMessenger) {
+      this.binaryMessenger = argBinaryMessenger;
+    }
+
+    public interface Reply<T> {
+      void reply(T reply);
+    }
+    /** The codec used by WebViewFlutterApi. */
+    static MessageCodec<Object> getCodec() {
+      return new StandardMessageCodec();
+    }
+
+    public void onScrollPosChange(
+        @NonNull Long webViewInstanceIdArg,
+        @NonNull Long xArg,
+        @NonNull Long yArg,
+        @NonNull Long oldXArg,
+        @NonNull Long oldYArg,
+        Reply<Void> callback) {
+      BasicMessageChannel<Object> channel =
+          new BasicMessageChannel<>(
+              binaryMessenger,
+              "dev.flutter.pigeon.WebViewFlutterApi.onScrollPosChange",
+              getCodec());
+      channel.send(
+          new ArrayList<Object>(Arrays.asList(webViewInstanceIdArg, xArg, yArg, oldXArg, oldYArg)),
+          channelReply -> {
+            callback.reply(null);
+          });
+    }
+  }
   /** Generated interface from Pigeon that represents a handler of messages from Flutter. */
   public interface WebChromeClientHostApi {
     void create(@NonNull Long instanceId);

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

@@ -0,0 +1,12 @@
+// Copyright 2013 The Flutter 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 androidx.annotation.Nullable;
+/** Define extending APIs for {@link android.webkit.WebView} */
+public interface WebViewExtendedApi {
+  void setContentOffsetChangedListener(
+      @Nullable ContentOffsetChangedListener contentOffsetChangedListener);
+}

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

@@ -0,0 +1,39 @@
+// Copyright 2013 The Flutter 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.webkit.WebView;
+import io.flutter.plugin.common.BinaryMessenger;
+import io.flutter.plugins.webviewflutter.GeneratedAndroidWebView.WebViewFlutterApi;
+
+/**
+ * Flutter Api implementation for {@link ContentOffsetChangedListener}.
+ *
+ * <p>Passes arguments of callbacks methods from a {@link ContentOffsetChangedListener} to Dart.
+ */
+public class WebViewFlutterApiImpl extends WebViewFlutterApi {
+  private final InstanceManager instanceManager;
+
+  /**
+   * Creates a Flutter api that sends messages to Dart.
+   *
+   * @param binaryMessenger handles sending messages to Dart
+   * @param instanceManager maintains instances stored to communicate with Dart objects
+   */
+  public WebViewFlutterApiImpl(BinaryMessenger binaryMessenger, InstanceManager instanceManager) {
+    super(binaryMessenger);
+    this.instanceManager = instanceManager;
+  }
+
+  /** Passes arguments from {@link ContentOffsetChangedListener#onContentOffsetChange} to Dart. */
+  public void onScrollPosChange(
+      WebView webView, long x, long y, long oldX, long oldY, Reply<Void> callback) {
+    final Long webViewIdentifier = instanceManager.getIdentifierForStrongReference(webView);
+    if (webViewIdentifier == null) {
+      throw new IllegalStateException("Could not find identifier for WebView.");
+    }
+    onScrollPosChange(webViewIdentifier, x, y, oldX, oldY, callback);
+  }
+}

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

@@ -92,6 +92,7 @@ private void setUp(
             instanceManager,
             binaryMessenger,
             new WebViewHostApiImpl.WebViewProxy(),
+            new WebViewFlutterApiImpl(binaryMessenger, instanceManager),
             context,
             containerView);
     javaScriptChannelHostApi =

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

@@ -16,6 +16,7 @@
 import androidx.annotation.Nullable;
 import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugin.platform.PlatformView;
+import io.flutter.plugins.webviewflutter.GeneratedAndroidWebView.WebViewFlutterApi;
 import io.flutter.plugins.webviewflutter.GeneratedAndroidWebView.WebViewHostApi;
 import java.util.Map;
 import java.util.Objects;
@@ -31,6 +32,7 @@ public class WebViewHostApiImpl implements WebViewHostApi {
   // Only used with WebView using virtual displays.
   @Nullable private final View containerView;
   private final BinaryMessenger binaryMessenger;
+  private final WebViewFlutterApi webViewFlutterApi;
 
   private Context context;
 
@@ -77,9 +79,11 @@ public void setWebContentsDebuggingEnabled(boolean enabled) {
   }
 
   /** Implementation of {@link WebView} that can be used as a Flutter {@link PlatformView}s. */
-  public static class WebViewPlatformView extends WebView implements PlatformView {
+  public static class WebViewPlatformView extends WebView
+      implements PlatformView, WebViewExtendedApi {
     private WebViewClient currentWebViewClient;
     private WebChromeClientHostApiImpl.SecureWebChromeClient currentWebChromeClient;
+    private @Nullable ContentOffsetChangedListener contentOffsetChangedListener;
 
     /**
      * Creates a {@link WebViewPlatformView}.
@@ -129,6 +133,20 @@ public void setWebChromeClient(WebChromeClient client) {
     public WebChromeClient getWebChromeClient() {
       return currentWebChromeClient;
     }
+
+    @Override
+    protected void onScrollChanged(int l, int t, int oldL, int oldT) {
+      super.onScrollChanged(l, t, oldL, oldT);
+      if (contentOffsetChangedListener != null) {
+        contentOffsetChangedListener.onContentOffsetChange(l, t, oldL, oldT);
+      }
+    }
+
+    @Override
+    public void setContentOffsetChangedListener(
+        ContentOffsetChangedListener contentOffsetChangedListener) {
+      this.contentOffsetChangedListener = contentOffsetChangedListener;
+    }
   }
 
   /**
@@ -137,9 +155,10 @@ public WebChromeClient getWebChromeClient() {
    */
   @SuppressLint("ViewConstructor")
   public static class InputAwareWebViewPlatformView extends InputAwareWebView
-      implements PlatformView {
+      implements PlatformView, WebViewExtendedApi {
     private WebViewClient currentWebViewClient;
     private WebChromeClientHostApiImpl.SecureWebChromeClient currentWebChromeClient;
+    private @Nullable ContentOffsetChangedListener contentOffsetChangedListener;
 
     /**
      * Creates a {@link InputAwareWebViewPlatformView}.
@@ -206,6 +225,20 @@ public void setWebChromeClient(WebChromeClient client) {
       currentWebChromeClient = (WebChromeClientHostApiImpl.SecureWebChromeClient) client;
       currentWebChromeClient.setWebViewClient(currentWebViewClient);
     }
+
+    @Override
+    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
+      super.onScrollChanged(l, t, oldl, oldt);
+      if (contentOffsetChangedListener != null) {
+        contentOffsetChangedListener.onContentOffsetChange(l, t, oldl, oldt);
+      }
+    }
+
+    @Override
+    public void setContentOffsetChangedListener(
+        ContentOffsetChangedListener contentOffsetChangedListener) {
+      this.contentOffsetChangedListener = contentOffsetChangedListener;
+    }
   }
 
   /**
@@ -221,11 +254,13 @@ public WebViewHostApiImpl(
       InstanceManager instanceManager,
       BinaryMessenger binaryMessenger,
       WebViewProxy webViewProxy,
+      WebViewFlutterApi webViewFlutterApi,
       Context context,
       @Nullable View containerView) {
     this.instanceManager = instanceManager;
     this.binaryMessenger = binaryMessenger;
     this.webViewProxy = webViewProxy;
+    this.webViewFlutterApi = webViewFlutterApi;
     this.context = context;
     this.containerView = containerView;
   }
@@ -420,6 +455,30 @@ public void setBackgroundColor(Long instanceId, Long color) {
     webView.setBackgroundColor(color.intValue());
   }
 
+  @Override
+  public void enableContentOffsetChangedListener(
+      @NonNull Long instanceId, @NonNull Boolean enabled) {
+    final WebView webView = (WebView) instanceManager.getInstance(instanceId);
+    if (webView instanceof WebViewExtendedApi) {
+      if (enabled) {
+        ((WebViewExtendedApi) webView)
+            .setContentOffsetChangedListener(
+                (left, top, oldLeft, oldTop) -> {
+                  webViewFlutterApi.onScrollPosChange(
+                      instanceId,
+                      (long) left,
+                      (long) top,
+                      (long) oldLeft,
+                      (long) oldTop,
+                      reply -> {});
+                });
+
+      } else {
+        ((WebViewExtendedApi) webView).setContentOffsetChangedListener(null);
+      }
+    }
+  }
+
   /** Maintains instances used to communicate with the corresponding WebView Dart object. */
   public InstanceManager getInstanceManager() {
     return instanceManager;

packages/webview_flutter/webview_flutter_android/android/src/test/java/io/flutter/plugins/webviewflutter/WebViewTest.java

@@ -6,7 +6,9 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.verify;
@@ -37,6 +39,8 @@ public class WebViewTest {
 
   @Mock WebViewHostApiImpl.WebViewProxy mockWebViewProxy;
 
+  @Mock public GeneratedAndroidWebView.WebViewFlutterApi mockWebViewFlutterApi;
+
   @Mock Context mockContext;
 
   @Mock BinaryMessenger mockBinaryMessenger;
@@ -52,7 +56,12 @@ public void setUp() {
         .thenReturn(mockWebView);
     testHostApiImpl =
         new WebViewHostApiImpl(
-            testInstanceManager, mockBinaryMessenger, mockWebViewProxy, mockContext, null);
+            testInstanceManager,
+            mockBinaryMessenger,
+            mockWebViewProxy,
+            mockWebViewFlutterApi,
+            mockContext,
+            null);
     testHostApiImpl.create(0L, true);
   }
 
@@ -314,4 +323,21 @@ public void destroy() {
 
     assertTrue(destroyCalled[0]);
   }
+
+  @Test
+  public void disableContentOffsetChangedListener() {
+    testHostApiImpl.enableContentOffsetChangedListener(0L, false);
+    verify(mockWebView).setContentOffsetChangedListener(null);
+  }
+
+  @Test
+  public void enableContentOffsetChangedListener() {
+    final ArgumentCaptor<ContentOffsetChangedListener> modeCaptor =
+        ArgumentCaptor.forClass(ContentOffsetChangedListener.class);
+    testHostApiImpl.enableContentOffsetChangedListener(0L, true);
+    verify(mockWebView).setContentOffsetChangedListener(modeCaptor.capture());
+    assertNotNull(modeCaptor.getValue());
+    modeCaptor.getValue().onContentOffsetChange(0, 1, 2, 3);
+    verify(mockWebViewFlutterApi).onScrollPosChange(eq(0L), eq(0L), eq(1L), eq(2L), eq(3L), any());
+  }
 }