Adds a type parameter to invokeMethod (and additional utility methods) (#26303)

dev/integration_tests/android_semantics_testing/lib/main.dart

@@ -26,7 +26,7 @@ Future<String> dataHandler(String message) async {
     final Completer<String> completer = Completer<String>();
     final int id = int.tryParse(message.split('#')[1]) ?? 0;
     Future<void> completeSemantics([Object _]) async {
-      final dynamic result = await kSemanticsChannel.invokeMethod('getSemanticsNode', <String, dynamic>{
+      final dynamic result = await kSemanticsChannel.invokeMethod<dynamic>('getSemanticsNode', <String, dynamic>{
         'id': id,
       });
       completer.complete(json.encode(result));

dev/integration_tests/android_views/lib/main.dart

@@ -125,15 +125,15 @@ class PlatformViewState extends State<PlatformViewPage> {
           .cast<Map<dynamic, dynamic>>()
           .map<Map<String, dynamic>>((Map<dynamic, dynamic> e) =>e.cast<String, dynamic>())
           .toList();
-      await channel.invokeMethod('pipeFlutterViewEvents');
-      await viewChannel.invokeMethod('pipeTouchEvents');
+      await channel.invokeMethod<void>('pipeFlutterViewEvents');
+      await viewChannel.invokeMethod<void>('pipeTouchEvents');
       print('replaying ${recordedEvents.length} motion events');
       for (Map<String, dynamic> event in recordedEvents.reversed) {
-        await channel.invokeMethod('synthesizeEvent', event);
+        await channel.invokeMethod<void>('synthesizeEvent', event);
       }
 
-      await channel.invokeMethod('stopFlutterViewEvents');
-      await viewChannel.invokeMethod('stopTouchEvents');
+      await channel.invokeMethod<void>('stopFlutterViewEvents');
+      await viewChannel.invokeMethod<void>('stopTouchEvents');
 
       if (flutterViewEvents.length != embeddedViewEvents.length)
         return 'Synthesized ${flutterViewEvents.length} events but the embedded view received ${embeddedViewEvents.length} events';
@@ -160,7 +160,7 @@ class PlatformViewState extends State<PlatformViewPage> {
   }
 
   Future<void> saveRecordedEvents(ByteData data, BuildContext context) async {
-    if (!await channel.invokeMethod('getStoragePermission')) {
+    if (!await channel.invokeMethod<bool>('getStoragePermission')) {
       showMessage(
           context, 'External storage permissions are required to save events');
       return;
@@ -190,11 +190,11 @@ class PlatformViewState extends State<PlatformViewPage> {
   }
 
   void listenToFlutterViewEvents() {
-    channel.invokeMethod('pipeFlutterViewEvents');
-    viewChannel.invokeMethod('pipeTouchEvents');
+    channel.invokeMethod<void>('pipeFlutterViewEvents');
+    viewChannel.invokeMethod<void>('pipeTouchEvents');
     Timer(const Duration(seconds: 3), () {
-      channel.invokeMethod('stopFlutterViewEvents');
-      viewChannel.invokeMethod('stopTouchEvents');
+      channel.invokeMethod<void>('stopFlutterViewEvents');
+      viewChannel.invokeMethod<void>('stopTouchEvents');
     });
   }
 

dev/integration_tests/channels/lib/src/method_calls.dart

@@ -67,7 +67,7 @@ Future<TestStepResult> _methodCallSuccessHandshake(
   dynamic result = nothing;
   dynamic error = nothing;
   try {
-    result = await channel.invokeMethod('success', arguments);
+    result = await channel.invokeMethod<dynamic>('success', arguments);
   } catch (e) {
     error = e;
   }
@@ -95,7 +95,7 @@ Future<TestStepResult> _methodCallErrorHandshake(
   dynamic errorDetails = nothing;
   dynamic error = nothing;
   try {
-    error = await channel.invokeMethod('error', arguments);
+    error = await channel.invokeMethod<dynamic>('error', arguments);
   } on PlatformException catch (e) {
     errorDetails = e.details;
   } catch (e) {
@@ -123,7 +123,7 @@ Future<TestStepResult> _methodCallNotImplementedHandshake(
   dynamic result = nothing;
   dynamic error = nothing;
   try {
-    error = await channel.invokeMethod('notImplemented');
+    error = await channel.invokeMethod<dynamic>('notImplemented');
   } on MissingPluginException {
     result = null;
   } catch (e) {

dev/integration_tests/external_ui/lib/main.dart

@@ -47,11 +47,11 @@ Widget builds: $_widgetBuilds''';
         _summary = 'Producing texture frames at .5x speed...';
         _state = FrameState.slow;
         _icon = Icons.stop;
-        channel.invokeMethod('start', _flutterFrameRate ~/ 2);
+        channel.invokeMethod<void>('start', _flutterFrameRate ~/ 2);
         break;
       case FrameState.slow:
         debugPrint('Stopping .5x speed test...');
-        await channel.invokeMethod('stop');
+        await channel.invokeMethod<void>('stop');
         await _summarizeStats();
         _icon = Icons.fast_forward;
         _state = FrameState.afterSlow;
@@ -62,11 +62,11 @@ Widget builds: $_widgetBuilds''';
         _summary = 'Producing texture frames at 2x speed...';
         _state = FrameState.fast;
         _icon = Icons.stop;
-        channel.invokeMethod('start', (_flutterFrameRate * 2).toInt());
+        channel.invokeMethod<void>('start', (_flutterFrameRate * 2).toInt());
         break;
       case FrameState.fast:
         debugPrint('Stopping 2x speed test...');
-        await channel.invokeMethod('stop');
+        await channel.invokeMethod<void>('stop');
         await _summarizeStats();
         _state = FrameState.afterFast;
         _icon = Icons.replay;

dev/integration_tests/flavors/lib/main.dart

@@ -18,7 +18,7 @@ class _FlavorState extends State<Flavor> {
   @override
   void initState() {
     super.initState();
-    const MethodChannel('flavor').invokeMethod('getFlavor').then((Object flavor) {
+    const MethodChannel('flavor').invokeMethod<String>('getFlavor').then((String flavor) {
       setState(() {
         _flavor = flavor;
       });

examples/flutter_gallery/test/live_smoketest.dart

@@ -82,10 +82,10 @@ Future<void> main() async {
       await controller.tap(find.byTooltip('Back'));
     }
     print('Finished successfully!');
-    _kTestChannel.invokeMethod('success');
+    _kTestChannel.invokeMethod<void>('success');
   } catch (error, stack) {
     print('Caught error: $error\n$stack');
-    _kTestChannel.invokeMethod('failure');
+    _kTestChannel.invokeMethod<void>('failure');
   }
 }
 

packages/flutter/lib/src/services/clipboard.dart

@@ -34,7 +34,7 @@ class Clipboard {
 
   /// Stores the given clipboard data on the clipboard.
   static Future<void> setData(ClipboardData data) async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'Clipboard.setData',
       <String, dynamic>{
         'text': data.text,

packages/flutter/lib/src/services/haptic_feedback.dart

@@ -21,7 +21,7 @@ class HapticFeedback {
   /// On Android, this uses the platform haptic feedback API to simulate a
   /// response to a long press (`HapticFeedbackConstants.LONG_PRESS`).
   static Future<void> vibrate() async {
-    await SystemChannels.platform.invokeMethod('HapticFeedback.vibrate');
+    await SystemChannels.platform.invokeMethod<void>('HapticFeedback.vibrate');
   }
 
   /// Provides a haptic feedback corresponding a collision impact with a light mass.
@@ -32,7 +32,7 @@ class HapticFeedback {
   ///
   /// On Android, this uses `HapticFeedbackConstants.VIRTUAL_KEY`.
   static Future<void> lightImpact() async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'HapticFeedback.vibrate',
       'HapticFeedbackType.lightImpact',
     );
@@ -46,7 +46,7 @@ class HapticFeedback {
   ///
   /// On Android, this uses `HapticFeedbackConstants.KEYBOARD_TAP`.
   static Future<void> mediumImpact() async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'HapticFeedback.vibrate',
       'HapticFeedbackType.mediumImpact',
     );
@@ -61,7 +61,7 @@ class HapticFeedback {
   /// On Android, this uses `HapticFeedbackConstants.CONTEXT_CLICK` on API levels
   /// 23 and above. This call has no effects on Android API levels below 23.
   static Future<void> heavyImpact() async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'HapticFeedback.vibrate',
       'HapticFeedbackType.heavyImpact',
     );
@@ -74,7 +74,7 @@ class HapticFeedback {
   ///
   /// On Android, this uses `HapticFeedbackConstants.CLOCK_TICK`.
   static Future<void> selectionClick() async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'HapticFeedback.vibrate',
       'HapticFeedbackType.selectionClick',
     );

packages/flutter/lib/src/services/platform_channel.dart

@@ -128,6 +128,12 @@ class MethodChannel {
   /// result. The values supported by the default codec and their platform-specific
   /// counterparts are documented with [StandardMessageCodec].
   ///
+  /// The generic argument `T` of the method can be inferred by the surrounding
+  /// context, or provided explicitly. If it does not match the returned type of
+  /// the channel, a [TypeError] will be thrown at runtime. `T` cannot be a class
+  /// with generics other than `dynamic`. For example, `Map<String, String>`
+  /// is not supported but `Map<dynamic, dynamic>` or `Map` is.
+  ///
   /// Returns a [Future] which completes to one of the following:
   ///
   /// * a result (possibly null), on successful invocation;
@@ -149,10 +155,9 @@ class MethodChannel {
   ///   static const MethodChannel _channel = MethodChannel('music');
   ///
   ///   static Future<bool> isLicensed() async {
-  ///     // invokeMethod returns a Future<dynamic>, and we cannot pass that for
-  ///     // a Future<bool>, hence the indirection.
-  ///     final bool result = await _channel.invokeMethod('isLicensed');
-  ///     return result;
+  ///     // invokeMethod returns a Future<T> which can be inferred as bool
+  ///     // in this context.
+  ///     return _channel.invokeMethod('isLicensed');
   ///   }
   ///
   ///   static Future<List<Song>> songs() async {
@@ -160,6 +165,7 @@ class MethodChannel {
   ///     // List<dynamic> with Map<dynamic, dynamic> entries. Post-processing
   ///     // code thus cannot assume e.g. List<Map<String, String>> even though
   ///     // the actual values involved would support such a typed container.
+  ///     // The correct type cannot be inferred with any value of `T`.
   ///     final List<dynamic> songs = await _channel.invokeMethod('getSongs');
   ///     return songs.map(Song.fromJson).toList();
   ///   }
@@ -168,7 +174,7 @@ class MethodChannel {
   ///     // Errors occurring on the platform side cause invokeMethod to throw
   ///     // PlatformExceptions.
   ///     try {
-  ///       await _channel.invokeMethod('play', <String, dynamic>{
+  ///       return _channel.invokeMethod('play', <String, dynamic>{
   ///         'song': song.id,
   ///         'volume': volume,
   ///       });
@@ -275,21 +281,54 @@ class MethodChannel {
   ///
   /// See also:
   ///
+  ///  * [invokeListMethod], for automatically returning typed lists.
+  ///  * [invokeMapMethod], for automatically returning typed maps.
   ///  * [StandardMessageCodec] which defines the payload values supported by
   ///    [StandardMethodCodec].
   ///  * [JSONMessageCodec] which defines the payload values supported by
   ///    [JSONMethodCodec].
   ///  * <https://docs.flutter.io/javadoc/io/flutter/plugin/common/MethodCall.html>
   ///    for how to access method call arguments on Android.
-  Future<dynamic> invokeMethod(String method, [dynamic arguments]) async {
+  @optionalTypeArgs
+  Future<T> invokeMethod<T>(String method, [dynamic arguments]) async {
     assert(method != null);
-    final dynamic result = await BinaryMessages.send(
+    final ByteData result = await BinaryMessages.send(
       name,
       codec.encodeMethodCall(MethodCall(method, arguments)),
     );
-    if (result == null)
+    if (result == null) {
       throw MissingPluginException('No implementation found for method $method on channel $name');
-    return codec.decodeEnvelope(result);
+    }
+    final T typedResult = codec.decodeEnvelope(result);
+    return typedResult;
+  }
+
+  /// An implementation of [invokeMethod] that can return typed lists.
+  ///
+  /// Dart generics are reified, meaning that an untyped List<dynamic>
+  /// cannot masquerade as a List<T>. Since invokeMethod can only return
+  /// dynamic maps, we instead create a new typed list using [List.cast].
+  ///
+  /// See also:
+  ///
+  ///  * [invokeMethod], which this call delegates to.
+  Future<List<T>> invokeListMethod<T>(String method, [dynamic arguments]) async {
+    final List<dynamic> result = await invokeMethod<List<dynamic>>(method, arguments);
+    return result.cast<T>();
+  }
+
+  /// An implementation of [invokeMethod] that can return typed maps.
+  ///
+  /// Dart generics are reified, meaning that an untyped Map<dynamic, dynamic>
+  /// cannot masquerade as a Map<K, V>. Since invokeMethod can only return
+  /// dynamic maps, we instead create a new typed map using [Map.cast].
+  ///
+  /// See also:
+  ///
+  ///  * [invokeMethod], which this call delegates to.
+  Future<Map<K, V>> invokeMapMethod<K, V>(String method, [dynamic arguments]) async {
+    final Map<dynamic, dynamic> result = await invokeMethod<Map<dynamic, dynamic>>(method, arguments);
+    return result.cast<K, V>();
   }
 
   /// Sets a callback for receiving method calls on this channel.
@@ -366,13 +405,27 @@ class OptionalMethodChannel extends MethodChannel {
     : super(name, codec);
 
   @override
-  Future<dynamic> invokeMethod(String method, [dynamic arguments]) async {
+  Future<T> invokeMethod<T>(String method, [dynamic arguments]) async {
     try {
-      return await super.invokeMethod(method, arguments);
+      final T result = await super.invokeMethod<T>(method, arguments);
+      return result;
     } on MissingPluginException {
       return null;
     }
   }
+
+  @override
+  Future<List<T>> invokeListMethod<T>(String method, [dynamic arguments]) async {
+    final List<dynamic> result = await invokeMethod<List<dynamic>>(method, arguments);
+    return result.cast<T>();
+  }
+
+  @override
+  Future<Map<K, V>> invokeMapMethod<K, V>(String method, [dynamic arguments]) async {
+    final Map<dynamic, dynamic> result = await invokeMethod<Map<dynamic, dynamic>>(method, arguments);
+    return result.cast<K, V>();
+  }
+
 }
 
 /// A named channel for communicating with platform plugins using event streams.
@@ -434,7 +487,7 @@ class EventChannel {
         return null;
       });
       try {
-        await methodChannel.invokeMethod('listen', arguments);
+        await methodChannel.invokeMethod<void>('listen', arguments);
       } catch (exception, stack) {
         FlutterError.reportError(FlutterErrorDetails(
           exception: exception,
@@ -446,7 +499,7 @@ class EventChannel {
     }, onCancel: () async {
       BinaryMessages.setMessageHandler(name, null);
       try {
-        await methodChannel.invokeMethod('cancel', arguments);
+        await methodChannel.invokeMethod<void>('cancel', arguments);
       } catch (exception, stack) {
         FlutterError.reportError(FlutterErrorDetails(
           exception: exception,

packages/flutter/lib/src/services/platform_views.dart

@@ -129,7 +129,7 @@ class PlatformViewsService {
         paramsByteData.lengthInBytes,
       );
     }
-    await SystemChannels.platform_views.invokeMethod('create', args);
+    await SystemChannels.platform_views.invokeMethod<void>('create', args);
     return UiKitViewController._(id, layoutDirection);
   }
 }
@@ -485,7 +485,7 @@ class AndroidViewController {
   /// disposed.
   Future<void> dispose() async {
     if (_state == _AndroidViewState.creating || _state == _AndroidViewState.created)
-      await SystemChannels.platform_views.invokeMethod('dispose', id);
+      await SystemChannels.platform_views.invokeMethod<void>('dispose', id);
     _state = _AndroidViewState.disposed;
   }
 
@@ -504,7 +504,7 @@ class AndroidViewController {
     if (_state == _AndroidViewState.waitingForSize)
       return _create(size);
 
-    await SystemChannels.platform_views.invokeMethod('resize', <String, dynamic> {
+    await SystemChannels.platform_views.invokeMethod<void>('resize', <String, dynamic> {
       'id': id,
       'width': size.width,
       'height': size.height,
@@ -526,7 +526,7 @@ class AndroidViewController {
     if (_state == _AndroidViewState.waitingForSize)
       return;
 
-    await SystemChannels.platform_views.invokeMethod('setDirection', <String, dynamic> {
+    await SystemChannels.platform_views.invokeMethod<void>('setDirection', <String, dynamic> {
       'id': id,
       'direction': _getAndroidDirection(layoutDirection),
     });
@@ -550,7 +550,7 @@ class AndroidViewController {
   /// See documentation of [MotionEvent.obtain](https://developer.android.com/reference/android/view/MotionEvent.html#obtain(long,%20long,%20int,%20float,%20float,%20float,%20float,%20int,%20float,%20float,%20int,%20int))
   /// for description of the parameters.
   Future<void> sendMotionEvent(AndroidMotionEvent event) async {
-    await SystemChannels.platform_views.invokeMethod(
+    await SystemChannels.platform_views.invokeMethod<dynamic>(
         'touch',
         event._asList(id),
     );
@@ -649,6 +649,6 @@ class UiKitViewController {
   /// disposed.
   Future<void> dispose() async {
     _debugDisposed = true;
-    await SystemChannels.platform_views.invokeMethod('dispose', id);
+    await SystemChannels.platform_views.invokeMethod<void>('dispose', id);
   }
 }

packages/flutter/lib/src/services/system_chrome.dart

@@ -238,7 +238,7 @@ class SystemChrome {
   /// The empty list causes the application to defer to the operating system
   /// default.
   static Future<void> setPreferredOrientations(List<DeviceOrientation> orientations) async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'SystemChrome.setPreferredOrientations',
       _stringify(orientations),
     );
@@ -250,7 +250,7 @@ class SystemChrome {
   /// Any part of the description that is unsupported on the current platform
   /// will be ignored.
   static Future<void> setApplicationSwitcherDescription(ApplicationSwitcherDescription description) async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'SystemChrome.setApplicationSwitcherDescription',
       <String, dynamic>{
         'label': description.label,
@@ -282,7 +282,7 @@ class SystemChrome {
   /// or calling this again. Otherwise, the original UI overlay settings will be
   /// automatically restored only when the application loses and regains focus.
   static Future<void> setEnabledSystemUIOverlays(List<SystemUiOverlay> overlays) async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'SystemChrome.setEnabledSystemUIOverlays',
       _stringify(overlays),
     );
@@ -298,7 +298,7 @@ class SystemChrome {
   /// On Android, the system UI cannot be changed until 1 second after the previous
   /// change. This is to prevent malware from permanently hiding navigation buttons.
   static Future<void> restoreSystemUIOverlays() async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'SystemChrome.restoreSystemUIOverlays',
       null,
     );
@@ -349,7 +349,7 @@ class SystemChrome {
     scheduleMicrotask(() {
       assert(_pendingStyle != null);
       if (_pendingStyle != _latestStyle) {
-        SystemChannels.platform.invokeMethod(
+        SystemChannels.platform.invokeMethod<void>(
           'SystemChrome.setSystemUIOverlayStyle',
           _pendingStyle._toMap(),
         );

packages/flutter/lib/src/services/system_navigator.dart

@@ -20,6 +20,6 @@ class SystemNavigator {
   /// the latter may cause the underlying platform to act as if the application
   /// had crashed.
   static Future<void> pop() async {
-    await SystemChannels.platform.invokeMethod('SystemNavigator.pop');
+    await SystemChannels.platform.invokeMethod<void>('SystemNavigator.pop');
   }
 }

packages/flutter/lib/src/services/system_sound.dart

@@ -20,7 +20,7 @@ class SystemSound {
   /// Play the specified system sound. If that sound is not present on the
   /// system, the call is ignored.
   static Future<void> play(SystemSoundType type) async {
-    await SystemChannels.platform.invokeMethod(
+    await SystemChannels.platform.invokeMethod<void>(
       'SystemSound.play',
       type.toString(),
     );

packages/flutter/lib/src/services/text_input.dart

@@ -626,13 +626,13 @@ class TextInputConnection {
   /// Requests that the text input control become visible.
   void show() {
     assert(attached);
-    SystemChannels.textInput.invokeMethod('TextInput.show');
+    SystemChannels.textInput.invokeMethod<void>('TextInput.show');
   }
 
   /// Requests that the text input control change its internal state to match the given state.
   void setEditingState(TextEditingValue value) {
     assert(attached);
-    SystemChannels.textInput.invokeMethod(
+    SystemChannels.textInput.invokeMethod<void>(
       'TextInput.setEditingState',
       value.toJSON(),
     );
@@ -644,7 +644,7 @@ class TextInputConnection {
   /// other client attaches to it within this animation frame.
   void close() {
     if (attached) {
-      SystemChannels.textInput.invokeMethod('TextInput.clearClient');
+      SystemChannels.textInput.invokeMethod<void>('TextInput.clearClient');
       _clientHandler
         .._currentConnection = null
         .._scheduleHide();
@@ -749,7 +749,7 @@ class _TextInputClientHandler {
     scheduleMicrotask(() {
       _hidePending = false;
       if (_currentConnection == null)
-        SystemChannels.textInput.invokeMethod('TextInput.hide');
+        SystemChannels.textInput.invokeMethod<void>('TextInput.hide');
     });
   }
 }
@@ -802,7 +802,7 @@ class TextInput {
     assert(_debugEnsureInputActionWorksOnPlatform(configuration.inputAction));
     final TextInputConnection connection = TextInputConnection._(client);
     _clientHandler._currentConnection = connection;
-    SystemChannels.textInput.invokeMethod(
+    SystemChannels.textInput.invokeMethod<void>(
       'TextInput.setClient',
       <dynamic>[ connection._id, configuration.toJson() ],
     );

packages/flutter/test/services/platform_channel_test.dart

@@ -43,15 +43,49 @@ void main() {
         'ch7',
         (ByteData message) async {
           final Map<dynamic, dynamic> methodCall = jsonMessage.decodeMessage(message);
-          if (methodCall['method'] == 'sayHello')
+          if (methodCall['method'] == 'sayHello') {
             return jsonMessage.encodeMessage(<dynamic>['${methodCall['args']} world']);
-          else
+          } else {
             return jsonMessage.encodeMessage(<dynamic>['unknown', null, null]);
+          }
         },
       );
       final String result = await channel.invokeMethod('sayHello', 'hello');
       expect(result, equals('hello world'));
     });
+    test('can invoke list method and get result', () async {
+      BinaryMessages.setMockMessageHandler(
+        'ch7',
+        (ByteData message) async {
+          final Map<dynamic, dynamic> methodCall = jsonMessage.decodeMessage(message);
+          if (methodCall['method'] == 'sayHello') {
+            return jsonMessage.encodeMessage(<dynamic>[<String>['${methodCall['args']}', 'world']]);
+          } else {
+            return jsonMessage.encodeMessage(<dynamic>['unknown', null, null]);
+          }
+        },
+      );
+      expect(channel.invokeMethod<List<String>>('sayHello', 'hello'), throwsA(isInstanceOf<TypeError>()));
+      expect(await channel.invokeListMethod<String>('sayHello', 'hello'), <String>['hello', 'world']);
+    });
+
+
+    test('can invoke map method and get result', () async {
+      BinaryMessages.setMockMessageHandler(
+        'ch7',
+        (ByteData message) async {
+          final Map<dynamic, dynamic> methodCall = jsonMessage.decodeMessage(message);
+          if (methodCall['method'] == 'sayHello') {
+            return jsonMessage.encodeMessage(<dynamic>[<String, String>{'${methodCall['args']}': 'world'}]);
+          } else {
+            return jsonMessage.encodeMessage(<dynamic>['unknown', null, null]);
+          }
+        },
+      );
+      expect(channel.invokeMethod<Map<String, String>>('sayHello', 'hello'), throwsA(isInstanceOf<TypeError>()));
+      expect(await channel.invokeMapMethod<String, String>('sayHello', 'hello'), <String, String>{'hello': 'world'});
+    });
+
     test('can invoke method and get error', () async {
       BinaryMessages.setMockMessageHandler(
         'ch7',
@@ -64,7 +98,7 @@ void main() {
         },
       );
       try {
-        await channel.invokeMethod('sayHello', 'hello');
+        await channel.invokeMethod<dynamic>('sayHello', 'hello');
         fail('Exception expected');
       } on PlatformException catch (e) {
         expect(e.code, equals('bad'));
@@ -80,7 +114,7 @@ void main() {
         (ByteData message) async => null,
       );
       try {
-        await channel.invokeMethod('sayHello', 'hello');
+        await channel.invokeMethod<void>('sayHello', 'hello');
         fail('Exception expected');
       } on MissingPluginException catch (e) {
         expect(e.message, contains('sayHello'));