compose: Give MessageListPageState access to topic/content controllers

Then, widgets that have MessageListPageState in their ancestry will
be able to set the topic and content inputs as part of managing a
quote-and-reply interaction.

Author: chrisbobbe

lib/widgets/compose_box.dart

@@ -845,12 +845,18 @@ class _ComposeBoxLayout extends StatelessWidget {
           ]))));  }
 }
 
+abstract class ComposeBoxController<T extends StatefulWidget> extends State<T> {
+  ComposeTopicController? get topicController;
+  ComposeContentController get contentController;
+  FocusNode get contentFocusNode;
+}
+
 /// A compose box for use in a stream narrow.
 ///
 /// This offers a text input for the topic to send to,
 /// in addition to a text input for the message content.
 class _StreamComposeBox extends StatefulWidget {
-  const _StreamComposeBox({required this.narrow});
+  const _StreamComposeBox({super.key, required this.narrow});
 
   /// The narrow on view in the message list.
   final StreamNarrow narrow;
@@ -859,9 +865,14 @@ class _StreamComposeBox extends StatefulWidget {
   State<_StreamComposeBox> createState() => _StreamComposeBoxState();
 }
 
-class _StreamComposeBoxState extends State<_StreamComposeBox> {
+class _StreamComposeBoxState extends State<_StreamComposeBox> implements ComposeBoxController<_StreamComposeBox> {
+  @override ComposeTopicController get topicController => _topicController;
   final _topicController = ComposeTopicController();
+
+  @override ComposeContentController get contentController => _contentController;
   final _contentController = ComposeContentController();
+
+  @override FocusNode get contentFocusNode => _contentFocusNode;
   final _contentFocusNode = FocusNode();
 
   @override
@@ -900,16 +911,21 @@ class _StreamComposeBoxState extends State<_StreamComposeBox> {
 }
 
 class _FixedDestinationComposeBox extends StatefulWidget {
-  const _FixedDestinationComposeBox({required this.narrow});
+  const _FixedDestinationComposeBox({super.key, required this.narrow});
 
   final SendableNarrow narrow;
 
   @override
   State<_FixedDestinationComposeBox> createState() => _FixedDestinationComposeBoxState();
 }
 
-class _FixedDestinationComposeBoxState extends State<_FixedDestinationComposeBox> {
+class _FixedDestinationComposeBoxState extends State<_FixedDestinationComposeBox> implements ComposeBoxController<_FixedDestinationComposeBox>  {
+  @override ComposeTopicController? get topicController => null;
+
+  @override ComposeContentController get contentController => _contentController;
   final _contentController = ComposeContentController();
+
+  @override FocusNode get contentFocusNode => _contentFocusNode;
   final _contentFocusNode = FocusNode();
 
   @override
@@ -939,19 +955,20 @@ class _FixedDestinationComposeBoxState extends State<_FixedDestinationComposeBox
 }
 
 class ComposeBox extends StatelessWidget {
-  const ComposeBox({super.key, required this.narrow});
+  const ComposeBox({super.key, this.controllerKey, required this.narrow});
 
+  final GlobalKey<ComposeBoxController>? controllerKey;
   final Narrow narrow;
 
   @override
   Widget build(BuildContext context) {
     final narrow = this.narrow;
     if (narrow is StreamNarrow) {
-      return _StreamComposeBox(narrow: narrow);
+      return _StreamComposeBox(key: controllerKey, narrow: narrow);
     } else if (narrow is TopicNarrow) {
-      return _FixedDestinationComposeBox(narrow: narrow);
+      return _FixedDestinationComposeBox(key: controllerKey, narrow: narrow);
     } else if (narrow is DmNarrow) {
-      return _FixedDestinationComposeBox(narrow: narrow);
+      return _FixedDestinationComposeBox(key: controllerKey, narrow: narrow);
     } else if (narrow is AllMessagesNarrow) {
       return const SizedBox.shrink();
     } else {

lib/widgets/message_list.dart

@@ -29,6 +29,19 @@ class MessageListPage extends StatefulWidget {
 }
 
 class MessageListPageState extends State<MessageListPage> {
+  GlobalKey<ComposeBoxController> get composeBoxKey => _composeBoxKey;
+  final GlobalKey<ComposeBoxController> _composeBoxKey = GlobalKey();
+
+  /// A [ComposeBoxController], if this [MessageListPage] offers a compose box.
+  ///
+  /// Uses the inefficient [BuildContext.findAncestorStateOfType];
+  /// don't call this in a build method.
+  static ComposeBoxController? composeBoxControllerOf(BuildContext context) {
+    final messageListPageState = context.findAncestorStateOfType<MessageListPageState>();
+    assert(messageListPageState != null, 'No MessageListPageState ancestor');
+    return messageListPageState!.composeBoxKey.currentState;
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -48,7 +61,7 @@ class MessageListPageState extends State<MessageListPage> {
               child: Expanded(
                 child: MessageList(narrow: widget.narrow))),
 
-            ComposeBox(narrow: widget.narrow),
+            ComposeBox(controllerKey: _composeBoxKey, narrow: widget.narrow),
           ]))));
   }
 }