Introduce an AndroidView widget and a RenderAndroidView render object. (#19565)

RenderAndroidView is responsible for sizing and displaying an embedded
Android view.
AndroidView is responsible for creating and disposing the Android view
and is using RenderAndroidView to display it.

packages/flutter/lib/rendering.dart

@@ -48,6 +48,7 @@ export 'src/rendering/list_wheel_viewport.dart';
 export 'src/rendering/object.dart';
 export 'src/rendering/paragraph.dart';
 export 'src/rendering/performance_overlay.dart';
+export 'src/rendering/platform_view.dart';
 export 'src/rendering/proxy_box.dart';
 export 'src/rendering/rotated_box.dart';
 export 'src/rendering/shifted_box.dart';

packages/flutter/lib/src/rendering/platform_view.dart

@@ -0,0 +1,99 @@
+// Copyright 2018 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.
+
+import 'dart:async';
+import 'dart:ui';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+
+import 'box.dart';
+import 'layer.dart';
+import 'object.dart';
+
+
+enum _PlatformViewState {
+  uninitialized,
+  resizing,
+  ready,
+}
+
+/// A render object for an Android view.
+///
+/// [RenderAndroidView] is responsible for sizing and displaying an Android [View](https://developer.android.com/reference/android/view/View).
+///
+/// The render object's layout behavior is to fill all available space, the parent of this object must
+/// provide bounded layout constraints
+///
+/// See also:
+///  * [AndroidView] which is a widget that is used to show an Android view.
+///  * [PlatformViewsService] which is a service for controlling platform views.
+class RenderAndroidView extends RenderBox {
+
+  /// Creates a render object for an Android view.
+  RenderAndroidView({
+    @required AndroidViewController viewController,
+  }) : assert(viewController != null),
+       _viewController = viewController;
+
+  _PlatformViewState _state = _PlatformViewState.uninitialized;
+
+  /// The Android view controller for the Android view associated with this render object.
+  AndroidViewController get viewcontroller => _viewController;
+  AndroidViewController _viewController;
+  /// Sets a new Android view controller.
+  ///
+  /// `viewController` must not be null.
+  set viewController(AndroidViewController viewController) {
+    assert(_viewController != null);
+    _viewController = viewController;
+    _sizePlatformView();
+  }
+
+  @override
+  bool get sizedByParent => true;
+
+  @override
+  bool get alwaysNeedsCompositing => true;
+
+  @override
+  bool get isRepaintBoundary => true;
+
+  @override
+  void performResize() {
+    size = constraints.biggest;
+    _sizePlatformView();
+  }
+
+  Future<Null> _sizePlatformView() async {
+    if (_state == _PlatformViewState.resizing) {
+      return;
+    }
+
+    _state = _PlatformViewState.resizing;
+
+    Size targetSize;
+    do {
+      targetSize = size;
+      await _viewController.setSize(size);
+      // We've resized the platform view to targetSize, but it is possible that
+      // while we were resizing the render object's size was changed again.
+      // In that case we will resize the platform view again.
+    } while (size != targetSize);
+
+    _state = _PlatformViewState.ready;
+    markNeedsPaint();
+  }
+
+  @override
+  void paint(PaintingContext context, Offset offset) {
+    if (_viewController.textureId == null)
+      return;
+
+    context.addLayer(new TextureLayer(
+      rect: offset & size,
+      textureId: _viewController.textureId,
+    ));
+  }
+}

packages/flutter/lib/src/widgets/platform_view.dart

@@ -0,0 +1,124 @@
+// Copyright 2018 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.
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/services.dart';
+
+import 'framework.dart';
+
+/// Embeds an Android view in the Widget hierarchy.
+///
+/// Embedding Android views is an expensive operation and should be avoided when a Flutter
+/// equivalent is possible.
+///
+/// The embedded Android view is painted just like any other Flutter widget and transformations
+/// apply to it as well.
+///
+/// The widget fill all available space, the parent of this object must provide bounded layout
+/// constraints.
+///
+/// The Android view object is created using a [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html).
+/// Plugins can register platform view factories with [PlatformViewRegistry#registerViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewRegistry.html#registerViewFactory-java.lang.String-io.flutter.plugin.platform.PlatformViewFactory-).
+///
+/// Registration is typically done in the plugin's registerWith method, e.g:
+///
+/// ```java
+///   public static void registerWith(Registrar registrar) {
+///     registrar.platformViewRegistry().registerViewFactory("webview", new WebViewFactory(registrar.messenger()));
+///   }
+/// ```
+///
+/// The Android view's lifetime is the same as the lifetime of the [State] object for this widget.
+/// When the [State] is disposed the platform view (and auxiliary resources) are lazily
+/// released (some resources are immediately released and some by platform garbage collector).
+/// A stateful widget's state is disposed the the widget is removed from the tree or when it is
+/// moved within the tree. If the stateful widget has a key and it's only moved relative to its siblings,
+/// or it has a [GlobalKey] and it's moved within the tree, it will not be disposed.
+class AndroidView extends StatefulWidget {
+  /// Creates a widget that embeds an Android view.
+  ///
+  /// The `viewType` parameter must not be null.
+  const AndroidView({
+    Key key,
+    @required this.viewType,
+    this.onPlatformViewCreated
+  }) : assert(viewType != null),
+       super(key: key);
+
+  /// The unique identifier for Android view type to be embedded by this widget.
+  /// A [PlatformViewFactory](/javadoc/io/flutter/plugin/platform/PlatformViewFactory.html)
+  /// for this type must have been registered.
+  ///
+  /// See also: [AndroidView] for an example of registering a platform view factory.
+  final String viewType;
+
+  /// Callback to invoke when after the Android view has been created.
+  ///
+  /// May be null.
+  final OnPlatformViewCreated onPlatformViewCreated;
+
+  @override
+  State createState() => new _AndroidViewState();
+}
+
+class _AndroidViewState extends State<AndroidView> {
+  int _id;
+  AndroidViewController _controller;
+
+  @override
+  Widget build(BuildContext context) {
+    return new _AndroidPlatformView(controller: _controller);
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    _createNewAndroidView();
+  }
+
+  @override
+  void didUpdateWidget(AndroidView oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (widget.viewType == oldWidget.viewType)
+      return;
+    _controller.dispose();
+    _createNewAndroidView();
+  }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
+  void _createNewAndroidView() {
+    _id = platformViewsRegistry.getNextPlatformViewId();
+    _controller = PlatformViewsService.initAndroidView(
+        id: _id,
+        viewType: widget.viewType,
+        onPlatformViewCreated: widget.onPlatformViewCreated
+    );
+  }
+
+}
+
+class _AndroidPlatformView extends LeafRenderObjectWidget {
+  const _AndroidPlatformView({
+    Key key,
+    @required this.controller,
+  }) : assert(controller != null),
+       super(key: key);
+
+  final AndroidViewController controller;
+
+  @override
+  RenderObject createRenderObject(BuildContext context) =>
+    new RenderAndroidView(viewController: controller);
+
+  @override
+  void updateRenderObject(BuildContext context, RenderAndroidView renderObject) {
+    renderObject.viewController = controller;
+  }
+}

packages/flutter/lib/widgets.dart

@@ -63,6 +63,7 @@ export 'src/widgets/page_view.dart';
 export 'src/widgets/pages.dart';
 export 'src/widgets/performance_overlay.dart';
 export 'src/widgets/placeholder.dart';
+export 'src/widgets/platform_view.dart';
 export 'src/widgets/preferred_size.dart';
 export 'src/widgets/primary_scroll_controller.dart';
 export 'src/widgets/raw_keyboard_listener.dart';

packages/flutter/test/widgets/platform_view_test.dart

@@ -0,0 +1,163 @@
+// Copyright 2018 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.
+
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/widgets.dart';
+
+import '../services/fake_platform_views.dart';
+
+void main() {
+
+  testWidgets('Create Android view', (WidgetTester tester) async {
+    final int currentViewId = platformViewsRegistry.getNextPlatformViewId();
+    final FakePlatformViewsController viewsController = new FakePlatformViewsController(TargetPlatform.android);
+    viewsController.registerViewType('webview');
+
+    await tester.pumpWidget(
+        const Center(
+            child: const SizedBox(
+              width: 200.0,
+              height: 100.0,
+              child: const AndroidView(viewType: 'webview'),
+            )
+        )
+    );
+
+    expect(
+      viewsController.views,
+      unorderedEquals(<FakePlatformView>[
+        new FakePlatformView(currentViewId + 1, 'webview', const Size(200.0, 100.0))
+      ])
+    );
+  });
+
+  testWidgets('Resize Android view', (WidgetTester tester) async {
+    final int currentViewId = platformViewsRegistry.getNextPlatformViewId();
+    final FakePlatformViewsController viewsController = new FakePlatformViewsController(TargetPlatform.android);
+    viewsController.registerViewType('webview');
+    await tester.pumpWidget(
+        const Center(
+            child: const SizedBox(
+              width: 200.0,
+              height: 100.0,
+              child: const AndroidView(viewType: 'webview'),
+            )
+        )
+    );
+
+    await tester.pumpWidget(
+        const Center(
+            child: const SizedBox(
+              width: 400.0,
+              height: 200.0,
+              child: const AndroidView(viewType: 'webview'),
+            )
+        )
+    );
+
+    expect(
+        viewsController.views,
+        unorderedEquals(<FakePlatformView>[
+          new FakePlatformView(currentViewId + 1, 'webview', const Size(400.0, 200.0))
+        ])
+    );
+  });
+
+  testWidgets('Change Android view type', (WidgetTester tester) async {
+    final int currentViewId = platformViewsRegistry.getNextPlatformViewId();
+    final FakePlatformViewsController viewsController = new FakePlatformViewsController(TargetPlatform.android);
+    viewsController.registerViewType('webview');
+    viewsController.registerViewType('maps');
+    await tester.pumpWidget(
+        const Center(
+            child: const SizedBox(
+              width: 200.0,
+              height: 100.0,
+              child: const AndroidView(viewType: 'webview'),
+            )
+        )
+    );
+
+    await tester.pumpWidget(
+        const Center(
+            child: const SizedBox(
+              width: 200.0,
+              height: 100.0,
+              child: const AndroidView(viewType: 'maps'),
+            )
+        )
+    );
+
+    expect(
+        viewsController.views,
+        unorderedEquals(<FakePlatformView>[
+          new FakePlatformView(currentViewId + 2, 'maps', const Size(200.0, 100.0))
+        ])
+    );
+  });
+
+  testWidgets('Dispose Android view', (WidgetTester tester) async {
+    final FakePlatformViewsController viewsController = new FakePlatformViewsController(TargetPlatform.android);
+    viewsController.registerViewType('webview');
+    await tester.pumpWidget(
+        const Center(
+            child: const SizedBox(
+              width: 200.0,
+              height: 100.0,
+              child: const AndroidView(viewType: 'webview'),
+            )
+        )
+    );
+
+    await tester.pumpWidget(
+        const Center(
+            child: const SizedBox(
+              width: 200.0,
+              height: 100.0,
+            )
+        )
+    );
+
+    expect(
+      viewsController.views,
+      isEmpty,
+    );
+  });
+
+  testWidgets('Android view survives widget tree change', (WidgetTester tester) async {
+    final int currentViewId = platformViewsRegistry.getNextPlatformViewId();
+    final FakePlatformViewsController viewsController = new FakePlatformViewsController(TargetPlatform.android);
+    viewsController.registerViewType('webview');
+    final GlobalKey key = new GlobalKey();
+    await tester.pumpWidget(
+        new Center(
+            child: new SizedBox(
+              width: 200.0,
+              height: 100.0,
+              child: new AndroidView(viewType: 'webview', key: key),
+            )
+        )
+    );
+
+    await tester.pumpWidget(
+      new Center(
+        child: new Container(
+          child: new SizedBox(
+            width: 200.0,
+            height: 100.0,
+            child: new AndroidView(viewType: 'webview', key: key),
+          ),
+        ),
+      ),
+    );
+
+    expect(
+        viewsController.views,
+        unorderedEquals(<FakePlatformView>[
+          new FakePlatformView(currentViewId + 1, 'webview', const Size(200.0, 100.0))
+        ])
+    );
+  });
+}