[macOS] Add initial support for raw key events

Implements the core of raw key event handling on macOS.

Uses the Android keyboard event structure, and only populates
part of it for now.

(Partially) addresses issue #72

Author: maun

example_flutter/lib/keyboard_test_page.dart

@@ -0,0 +1,99 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+import 'package:flutter/material.dart';
+import 'package:flutter/scheduler.dart';
+import 'package:flutter/services.dart';
+
+/// Keyboard test page for the example application.
+class KeyboardTestPage extends StatefulWidget {
+  @override
+  State<StatefulWidget> createState() {
+    return _KeyboardTestPageState();
+  }
+}
+
+class _KeyboardTestPageState extends State<KeyboardTestPage> {
+  final List<String> _messages = [];
+
+  final FocusNode _focusNode = FocusNode();
+  final ScrollController _scrollController = new ScrollController();
+
+  @override
+  void initState() {
+    super.initState();
+    FocusScope.of(context).requestFocus(_focusNode);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return new Scaffold(
+      appBar: AppBar(
+          title: new Text('Keyboard events test'),
+          leading: new IconButton(
+              icon: new Icon(Icons.arrow_back),
+              onPressed: () {
+                Navigator.of(context).pop();
+              })),
+      body: new RawKeyboardListener(
+        focusNode: _focusNode,
+        onKey: onKeyEvent,
+        child: Container(
+          padding: EdgeInsets.symmetric(horizontal: 16.0),
+          child: SingleChildScrollView(
+              controller: _scrollController,
+              child: Column(
+                  crossAxisAlignment: CrossAxisAlignment.start,
+                  children: _messages.map((m) => new Text(m)).toList())),
+        ),
+      ),
+    );
+  }
+
+  void onKeyEvent(RawKeyEvent event) {
+    bool isKeyDown;
+    switch (event.runtimeType) {
+      case RawKeyDownEvent:
+        isKeyDown = true;
+        break;
+      case RawKeyUpEvent:
+        isKeyDown = false;
+        break;
+      default:
+        throw new Exception('Unexpected runtimeType of RawKeyEvent');
+    }
+
+    int keyCode;
+    switch (event.data.runtimeType) {
+      case RawKeyEventDataAndroid:
+        final RawKeyEventDataAndroid data = event.data;
+        keyCode = data.keyCode;
+        break;
+      default:
+        throw new Exception('Unsupported platform');
+    }
+
+    _addMessage('${isKeyDown ? 'KeyDown' : 'KeyUp'}: $keyCode');
+  }
+
+  void _addMessage(String message) {
+    setState(() {
+      _messages.add(message);
+    });
+    SchedulerBinding.instance.addPostFrameCallback((_) {
+      _scrollController.jumpTo(
+        _scrollController.position.maxScrollExtent,
+      );
+    });
+  }
+}

example_flutter/lib/main.dart

@@ -18,6 +18,7 @@ import 'package:flutter/foundation.dart'
 import 'package:flutter/material.dart';
 
 import 'package:color_panel/color_panel.dart';
+import 'package:example_flutter/keyboard_test_page.dart';
 import 'package:file_chooser/file_chooser.dart' as file_chooser;
 import 'package:menubar/menubar.dart';
 
@@ -181,6 +182,12 @@ class _MyHomePage extends StatelessWidget {
             ),
             TextInputTestWidget(),
             FileChooserTestWidget(),
+            new RaisedButton(
+                child: new Text('Test raw keyboard events'),
+                onPressed: () {
+                  Navigator.of(context).push(new MaterialPageRoute(
+                      builder: (context) => KeyboardTestPage()));
+                })
           ],
         ),
       ),

macos/library/FLECodecs.h

@@ -55,7 +55,7 @@
  * A codec that uses JSON as the encoding format. Method arguments and error details for plugins
  * using this codec must be serializable to JSON.
  */
-@interface FLEJSONMethodCodec : NSObject<FLEMethodCodec>
+@interface FLEJSONMethodCodec : NSObject <FLEMethodCodec>
 @end
 
 // TODO: Implement the other core Flutter codecs. Issue #67.

macos/library/FLEKeyEventPlugin.h

@@ -0,0 +1,26 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#import <Cocoa/Cocoa.h>
+
+#import "FLEPlugin.h"
+
+/**
+ * A FlutterPlugin to handle raw keyboard events. Owned by the FlutterViewController.
+ * Responsible for bridging the native macOS keyboard event system with the
+ * Flutter framework raw keyboard event classes, via system channels.
+ */
+@interface FLEKeyEventPlugin : NSResponder <FLEPlugin>
+
+@end

macos/library/FLEKeyEventPlugin.m

@@ -0,0 +1,61 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#import "FLEKeyEventPlugin.h"
+
+#import "FLEViewController+Internal.h"
+#import "FLEViewController.h"
+
+static NSString *const kKeyEventChannel = @"flutter/keyevent";
+
+@implementation FLEKeyEventPlugin
+
+@synthesize controller = _controller;
+
+- (NSString *)channel {
+  return kKeyEventChannel;
+}
+
+- (void)handleMethodCall:(FLEMethodCall *)call result:(FLEMethodResult)result {
+  result(FLEMethodNotImplemented);
+}
+
+/**
+ * Sends a key event to flutter.
+ * @param event NSEvent received from the system.
+ * @param type Type of this key event. Can be either "keydown" or "keyup".
+ */
+- (void)dispatchKeyEvent:(NSEvent *)event ofType:(NSString *)type {
+  // TODO: Do not use 'android'. Reconsider when
+  // https://github.com/google/flutter-desktop-embedding/issues/47 is solved.
+  NSDictionary *message = @{
+    @"keymap" : @"android",
+    @"type" : type,
+    @"keyCode" : @(event.keyCode),
+  };
+
+  [self.controller dispatchMessage:message onChannel:kKeyEventChannel];
+}
+
+#pragma mark - NSResponder
+
+- (void)keyDown:(NSEvent *)event {
+  [self dispatchKeyEvent:event ofType:@"keydown"];
+}
+
+- (void)keyUp:(NSEvent *)event {
+  [self dispatchKeyEvent:event ofType:@"keyup"];
+}
+
+@end

macos/library/FLETextInputPlugin.m

@@ -17,7 +17,7 @@
 #import <objc/message.h>
 
 #import "FLETextInputModel.h"
-#import "FLEViewController.h"
+#import "FLEViewController+Internal.h"
 
 static NSString *const kTextInputChannel = @"flutter/textinput";
 
@@ -91,10 +91,10 @@ - (void)handleMethodCall:(FLEMethodCall *)call result:(FLEMethodResult)result {
       _textInputModels[_activeClientID] = [[FLETextInputModel alloc] init];
     }
   } else if ([method isEqualToString:kShowMethod]) {
-    [_controller.view.window makeFirstResponder:self];
+    [self.controller addKeyResponder:self];
     [_textInputContext activate];
   } else if ([method isEqualToString:kHideMethod]) {
-    [_controller.view.window makeFirstResponder:nil];
+    [self.controller removeKeyResponder:self];
     [_textInputContext deactivate];
   } else if ([method isEqualToString:kClearClientMethod]) {
     _activeClientID = nil;
@@ -124,10 +124,6 @@ - (void)updateEditState {
 #pragma mark -
 #pragma mark NSResponder
 
-- (BOOL)acceptsFirstResponder {
-  return YES;
-}
-
 /**
  * Note, the Apple docs suggest that clients should override essentially all the
  * mouse and keyboard event-handling methods of NSResponder. However, experimentation

macos/library/FLEViewController+Internal.h

@@ -0,0 +1,36 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#import "FLEViewController.h"
+
+@interface FLEViewController ()
+
+/**
+ * Adds a responder for keyboard events. Key up and key down events are forwarded to all added
+ * responders.
+ */
+- (void)addKeyResponder:(nonnull NSResponder *)responder;
+
+/**
+ * Removes a responder for keyboard events.
+ */
+- (void)removeKeyResponder:(nonnull NSResponder *)responder;
+
+/**
+ * Sends a platform message to the Flutter engine on the given channel.
+ * @param message The raw message.
+ */
+- (void)dispatchMessage:(nonnull NSDictionary *)message onChannel:(nonnull NSString *)channel;
+
+@end