Port google_maps_flutter to use AndroidView for embedding the map. (#743)

This change adds a GoogleMap widget which shows a map as part of the  widget tree.
Each map uses a dedicated method channel named 'plugins.flutter.io/google_maps_$id',
The Java GoogleMapsController class now extends PlatformView, and is the
Java endpoint of the per map method channel.

This change disables the plugin on iOS until we have an inlining solution
for iOS.

Author: amirh

packages/google_maps_flutter/README.md

@@ -2,8 +2,7 @@
 
 [![pub package](https://img.shields.io/pub/v/google_maps_flutter.svg)](https://pub.dartlang.org/packages/google_maps_flutter)
 
-A Flutter plugin to use [Google Maps](https://developers.google.com/maps/) in
-iOS and Android apps.
+A Flutter plugin to use [Google Maps](https://developers.google.com/maps/).
 
 ## Caveat
 
@@ -12,24 +11,9 @@ This plugin provides an *unpublished preview* of the Flutter API for Google Maps
   code are still being consolidated and expanded. The intention is to grow
   current coverage into a complete offering. Issues and pull requests aimed to
   help us prioritize and speed up this effort are very welcome.
-* The technique currently used for compositing GoogleMap views with Flutter
-  widgets is *inherently limited* and will be replaced by a fully compositional
-  [Texture](https://docs.flutter.io/flutter/widgets/Texture-class.html)-based
-  approach before we publish this plugin.
-
-  In detail: the plugin currently relies on placing platform overlays on top of
-  a bitmap snapshotting widget for creating the illusion of in-line compositing
-  of GoogleMap views with Flutter widgets. This works only in very limited
-  situations where
-  * the widget is stationary
-  * the widget is drawn on top of all other widgets within bounds
-  * touch events within widget bounds can be safely ignored by Flutter
-
-  The root problem with platform overlays is that they cannot be freely composed
-  with other widgets. Many workarounds can be devised to address this shortcoming
-  in particular situations, but the Flutter team does not intend to support such
-  work, as it would not move us forward towards our goal of a fully compositional
-  GoogleMaps widget.
+* Currently the plugin only supports Android as it embeds a platform view in the
+  Flutter hierarchy which is currently only supported for Android ([tracking
+  issue](https://github.com/flutter/flutter/issues/19030)).
 
 ## Usage
 
@@ -79,38 +63,32 @@ Supply your API key in the application delegate `ios/Runner/AppDelegate.m`:
 
 ### Both
 
-You can now instantiate a `GoogleMapOverlayController` and use it to configure
-a `GoogleMapOverlay` widget. Client code will have to change once the plugin
-stops using platform overlays.
+You can now add a `GoogleMap` widget to your widget tree.
 
-Once added as an overlay, the map view can be controlled via the
-`GoogleMapController` that you obtain as the `mapController` property of
-the overlay controller. Client code written against the `GoogleMapController`
-interface will be unaffected by the change away from platform overlays.
+The map view can be controlled with the `GoogleMapController` that is passed to
+the `GoogleMap`'s `onMapCreated` callback.
 
 ```dart
 import 'package:flutter/material.dart';
 import 'package:google_maps_flutter/google_maps_flutter.dart';
 
 void main() {
-  GoogleMapController.init();
-  final GoogleMapOverlayController controller =
-      GoogleMapOverlayController.fromSize(width: 300.0, height: 200.0);
-  final Widget mapWidget = GoogleMapOverlay(controller: controller);
   runApp(MaterialApp(
     home: new Scaffold(
       appBar: AppBar(title: const Text('Google Maps demo')),
-      body: MapsDemo(mapWidget, controller.mapController),
+      body: MapsDemo(),
     ),
-    navigatorObservers: <NavigatorObserver>[controller.overlayController],
   ));
 }
 
-class MapsDemo extends StatelessWidget {
-  MapsDemo(this.mapWidget, this.controller);
+class MapsDemo extends StatefulWidget {
+  @override
+  State createState() => MapsDemoState();
+}
+
+class MapsDemoState extends State<MapsDemo> {
 
-  final Widget mapWidget;
-  final GoogleMapController controller;
+  GoogleMapController mapController;
 
   @override
   Widget build(BuildContext context) {
@@ -119,11 +97,19 @@ class MapsDemo extends StatelessWidget {
       child: Column(
         mainAxisAlignment: MainAxisAlignment.spaceEvenly,
         children: <Widget>[
-          Center(child: mapWidget),
+          Center(
+            child: SizedBox(
+              width: 300.0,
+              height: 200.0,
+              child: GoogleMap(
+                onMapCreated: _onMapCreated,
+              ),
+            ),
+          ),
           RaisedButton(
             child: const Text('Go to London'),
-            onPressed: () {
-              controller.animateCamera(CameraUpdate.newCameraPosition(
+            onPressed: mapController == null ? null : () {
+              mapController.animateCamera(CameraUpdate.newCameraPosition(
                 const CameraPosition(
                   bearing: 270.0,
                   target: LatLng(51.5160895, -0.1294527),
@@ -137,6 +123,10 @@ class MapsDemo extends StatelessWidget {
       ),
     );
   }
+
+  void _onMapCreated(GoogleMapController controller) {
+    setState(() { mapController = controller; });
+  }
 }
 ```
 

packages/google_maps_flutter/android/src/main/java/io/flutter/plugins/googlemaps/GoogleMapBuilder.java

@@ -4,10 +4,10 @@
 
 package io.flutter.plugins.googlemaps;
 
+import android.content.Context;
 import com.google.android.gms.maps.GoogleMapOptions;
 import com.google.android.gms.maps.model.CameraPosition;
 import com.google.android.gms.maps.model.LatLngBounds;
-import io.flutter.plugin.common.MethodChannel;
 import io.flutter.plugin.common.PluginRegistry;
 import java.util.concurrent.atomic.AtomicInteger;
 
@@ -16,13 +16,9 @@ class GoogleMapBuilder implements GoogleMapOptionsSink {
   private boolean trackCameraPosition = false;
 
   GoogleMapController build(
-      AtomicInteger state,
-      PluginRegistry.Registrar registrar,
-      int width,
-      int height,
-      MethodChannel.Result result) {
+      int id, Context context, AtomicInteger state, PluginRegistry.Registrar registrar) {
     final GoogleMapController controller =
-        new GoogleMapController(state, registrar, width, height, options, result);
+        new GoogleMapController(id, context, state, registrar, options);
     controller.init();
     controller.setTrackCameraPosition(trackCameraPosition);
     return controller;