[webview_flutter] Move the method channel behind the platform interface

packages/webview_flutter/lib/platform_interface.dart

@@ -10,11 +10,35 @@ import 'package:flutter/widgets.dart';
 
 import 'webview_flutter.dart';
 
+/// Interface for callbacks made by [WebViewPlatform].
+///
+/// The webview plugin implements this class, and passes an instance to the [WebViewPlatform].
+/// [WebViewPlatform] is notifying this handler on events that happened on the platform's webview.
+abstract class WebViewPlatformCallbacksHandler {
+  /// Invoked by [WebViewPlatform] when a JavaScript channel message is received.
+  void onJavaScriptChannelMessage(String channel, String message);
+
+  /// Invoked by [WebViewPlatform] when a navigation request is pending.
+  ///
+  /// If true is returned the navigation is allowed, otherwise it is blocked.
+  bool onNavigationRequest({String url, bool isForMainFrame});
+
+  /// Invoked by [WebViewPlatform] when a page has finished loading.
+  void onPageFinished(String url);
+}
+
 /// Interface for talking to the webview's platform implementation.
 ///
 /// An instance implementing this interface is passed to the `onWebViewPlatformCreated` callback that is
 /// passed to [WebViewPlatformBuilder#onWebViewPlatformCreated].
 abstract class WebViewPlatform {
+  /// Creates a new WebViewPlatform.
+  ///
+  /// Callbacks made by the WebView will be delegated to `handler`.
+  ///
+  /// The `handler` parameter must not be null.
+  WebViewPlatform(WebViewPlatformCallbacksHandler handler);
+
   /// Loads the specified URL.
   ///
   /// If `headers` is not null and the URL is an HTTP URL, the key value paris in `headers` will
@@ -40,12 +64,94 @@ abstract class WebViewPlatform {
         "WebView updateSettings is not implemented on the current platform");
   }
 
-  // As the PR currently focus about the wiring I've only moved loadUrl to the new way, so
-  // the discussion is more focused.
-  // In this temporary state WebViewController still uses a method channel directly for all other
-  // method calls so we need to expose the webview ID.
-  // TODO(amirh): remove this before publishing this package.
-  int get id;
+  /// Accessor to the current URL that the WebView is displaying.
+  ///
+  /// If no URL was ever loaded, returns `null`.
+  Future<String> currentUrl() {
+    throw UnimplementedError(
+        "WebView currentUrl is not implemented on the current platform");
+  }
+
+  /// Checks whether there's a back history item.
+  Future<bool> canGoBack() {
+    throw UnimplementedError(
+        "WebView canGoBack is not implemented on the current platform");
+  }
+
+  /// Checks whether there's a forward history item.
+  Future<bool> canGoForward() {
+    throw UnimplementedError(
+        "WebView canGoForward is not implemented on the current platform");
+  }
+
+  /// Goes back in the history of this WebView.
+  ///
+  /// If there is no back history item this is a no-op.
+  Future<void> goBack() {
+    throw UnimplementedError(
+        "WebView goBack is not implemented on the current platform");
+  }
+
+  /// Goes forward in the history of this WebView.
+  ///
+  /// If there is no forward history item this is a no-op.
+  Future<void> goForward() {
+    throw UnimplementedError(
+        "WebView goForward is not implemented on the current platform");
+  }
+
+  /// Reloads the current URL.
+  Future<void> reload() {
+    throw UnimplementedError(
+        "WebView reload is not implemented on the current platform");
+  }
+
+  /// Clears all caches used by the [WebView].
+  ///
+  /// The following caches are cleared:
+  ///	1. Browser HTTP Cache.
+  ///	2. [Cache API](https://developers.google.com/web/fundamentals/instant-and-offline/web-storage/cache-api) caches.
+  ///    These are not yet supported in iOS WkWebView. Service workers tend to use this cache.
+  ///	3. Application cache.
+  ///	4. Local Storage.
+  Future<void> clearCache() {
+    throw UnimplementedError(
+        "WebView clearCache is not implemented on the current platform");
+  }
+
+  /// Evaluates a JavaScript expression in the context of the current page.
+  ///
+  /// The Future completes with an error if a JavaScript error occurred, or if the type of the
+  /// evaluated expression is not supported(e.g on iOS not all non primitive type can be evaluated).
+  Future<String> evaluateJavascript(String javascriptString) {
+    throw UnimplementedError(
+        "WebView evaluateJavascript is not implemented on the current platform");
+  }
+
+  /// Adds new JavaScript channels to the set of enabled channels.
+  ///
+  /// For each value in this list the platform's webview should make sure that a corresponding
+  /// property with a postMessage method is set on `window`. For example for a JavaScript channel
+  /// named `Foo` it should be possible for JavaScript code executing in the webview to do
+  ///
+  /// ```javascript
+  /// Foo.postMessage('hello');
+  /// ```
+  ///
+  /// See also: [CreationParams.javascriptChannelNames].
+  Future<void> addJavascriptChannels(Set<String> javascriptChannelNames) {
+    throw UnimplementedError(
+        "WebView addJavascriptChannels is not implemented on the current platform");
+  }
+
+  /// Removes JavaScript channel names from the set of enabled channels.
+  ///
+  /// This disables channels that were previously enabled by [addJavaScriptChannels] or through
+  /// [CreationParams.javascriptChannelNames].
+  Future<void> removeJavascriptChannels(Set<String> javascriptChannelNames) {
+    throw UnimplementedError(
+        "WebView removeJavascriptChannels is not implemented on the current platform");
+  }
 }
 
 /// Settings for configuring a WebViewPlatform.
@@ -125,6 +231,9 @@ abstract class WebViewBuilder {
   ///
   /// `creationParams` are the initial parameters used to setup the webview.
   ///
+  /// `webViewPlatformHandler` will be used for handling callbacks that are made by the created
+  /// [WebViewPlatform].
+  ///
   /// `onWebViewPlatformCreated` will be invoked after the platform specific [WebViewPlatform]
   /// implementation is created with the [WebViewPlatform] instance as a parameter.
   ///
@@ -135,12 +244,15 @@ abstract class WebViewBuilder {
   /// recognizers on this list.
   /// When `gestureRecognizers` is empty or null, the web view will only handle pointer events for gestures that
   /// were not claimed by any other gesture recognizer.
+  ///
+  /// `webViewPlatformHandler` must not be null.
   Widget build({
     BuildContext context,
     // TODO(amirh): convert this to be the actual parameters.
     // I'm starting without it as the PR is starting to become pretty big.
     // I'll followup with the conversion PR.
     CreationParams creationParams,
+    @required WebViewPlatformCallbacksHandler webViewPlatformCallbacksHandler,
     WebViewPlatformCreatedCallback onWebViewPlatformCreated,
     Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers,
   });

packages/webview_flutter/lib/src/webview_android.dart

@@ -20,9 +20,11 @@ class AndroidWebViewBuilder implements WebViewBuilder {
   Widget build({
     BuildContext context,
     CreationParams creationParams,
+    @required WebViewPlatformCallbacksHandler webViewPlatformCallbacksHandler,
     WebViewPlatformCreatedCallback onWebViewPlatformCreated,
     Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers,
   }) {
+    assert(webViewPlatformCallbacksHandler != null);
     return GestureDetector(
       // We prevent text selection by intercepting the long press event.
       // This is a temporary stop gap due to issues with text selection on Android:
@@ -39,7 +41,8 @@ class AndroidWebViewBuilder implements WebViewBuilder {
           if (onWebViewPlatformCreated == null) {
             return;
           }
-          onWebViewPlatformCreated(MethodChannelWebViewPlatform(id));
+          onWebViewPlatformCreated(MethodChannelWebViewPlatform(
+              id, webViewPlatformCallbacksHandler));
         },
         gestureRecognizers: gestureRecognizers,
         // WebView content is not affected by the Android view's layout direction,

packages/webview_flutter/lib/src/webview_cupertino.dart

@@ -20,6 +20,7 @@ class CupertinoWebViewBuilder implements WebViewBuilder {
   Widget build({
     BuildContext context,
     CreationParams creationParams,
+    @required WebViewPlatformCallbacksHandler webViewPlatformCallbacksHandler,
     WebViewPlatformCreatedCallback onWebViewPlatformCreated,
     Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers,
   }) {
@@ -29,7 +30,8 @@ class CupertinoWebViewBuilder implements WebViewBuilder {
         if (onWebViewPlatformCreated == null) {
           return;
         }
-        onWebViewPlatformCreated(MethodChannelWebViewPlatform(id));
+        onWebViewPlatformCreated(
+            MethodChannelWebViewPlatform(id, webViewPlatformCallbacksHandler));
       },
       gestureRecognizers: gestureRecognizers,
       creationParams:

packages/webview_flutter/lib/src/webview_method_channel.dart

@@ -10,13 +10,36 @@ import '../platform_interface.dart';
 
 /// A [WebViewPlatform] that uses a method channel to control the webview.
 class MethodChannelWebViewPlatform implements WebViewPlatform {
-  MethodChannelWebViewPlatform(this._id)
-      : _channel = MethodChannel('plugins.flutter.io/webview_$_id');
+  MethodChannelWebViewPlatform(int id, this._platformCallbacksHandler)
+      : assert(_platformCallbacksHandler != null),
+        _channel = MethodChannel('plugins.flutter.io/webview_$id') {
+    _channel.setMethodCallHandler(_onMethodCall);
+  }
 
-  final int _id;
+  final WebViewPlatformCallbacksHandler _platformCallbacksHandler;
 
   final MethodChannel _channel;
 
+  Future<bool> _onMethodCall(MethodCall call) async {
+    switch (call.method) {
+      case 'javascriptChannelMessage':
+        final String channel = call.arguments['channel'];
+        final String message = call.arguments['message'];
+        _platformCallbacksHandler.onJavaScriptChannelMessage(channel, message);
+        return true;
+      case 'navigationRequest':
+        return _platformCallbacksHandler.onNavigationRequest(
+          url: call.arguments['url'],
+          isForMainFrame: call.arguments['isForMainFrame'],
+        );
+      case 'onPageFinished':
+        _platformCallbacksHandler.onPageFinished(call.arguments['url']);
+        return null;
+    }
+    throw MissingPluginException(
+        '${call.method} was invoked but has no handler');
+  }
+
   @override
   Future<void> loadUrl(
     String url,
@@ -32,6 +55,27 @@ class MethodChannelWebViewPlatform implements WebViewPlatform {
     });
   }
 
+  @override
+  Future<String> currentUrl() => _channel.invokeMethod('currentUrl');
+
+  @override
+  Future<bool> canGoBack() => _channel.invokeMethod("canGoBack");
+
+  @override
+  Future<bool> canGoForward() => _channel.invokeMethod("canGoForward");
+
+  @override
+  Future<void> goBack() => _channel.invokeMethod("goBack");
+
+  @override
+  Future<void> goForward() => _channel.invokeMethod("goForward");
+
+  @override
+  Future<void> reload() => _channel.invokeMethod("reload");
+
+  @override
+  Future<void> clearCache() => _channel.invokeMethod("clearCache");
+
   @override
   Future<void> updateSettings(WebSettings settings) {
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
@@ -44,6 +88,23 @@ class MethodChannelWebViewPlatform implements WebViewPlatform {
     return _channel.invokeMethod('updateSettings', updatesMap);
   }
 
+  @override
+  Future<String> evaluateJavascript(String javascriptString) {
+    return _channel.invokeMethod('evaluateJavascript', javascriptString);
+  }
+
+  @override
+  Future<void> addJavascriptChannels(Set<String> javascriptChannelNames) {
+    return _channel.invokeMethod(
+        'addJavascriptChannels', javascriptChannelNames.toList());
+  }
+
+  @override
+  Future<void> removeJavascriptChannels(Set<String> javascriptChannelNames) {
+    return _channel.invokeMethod(
+        'removeJavascriptChannels', javascriptChannelNames.toList());
+  }
+
   static Map<String, dynamic> _webSettingsToMap(WebSettings settings) {
     final Map<String, dynamic> map = <String, dynamic>{};
     void _addIfNonNull(String key, dynamic value) {
@@ -71,7 +132,4 @@ class MethodChannelWebViewPlatform implements WebViewPlatform {
       'javascriptChannelNames': creationParams.javascriptChannelNames.toList(),
     };
   }
-
-  @override
-  int get id => _id;
 }