msglist: MessageList now has a scroll to bottom button

Author: sirpengi

lib/widgets/message_list.dart

@@ -97,6 +97,31 @@ class MessageListAppBarTitle extends StatelessWidget {
   }
 }
 
+class ScrollToBottomButton extends StatelessWidget {
+  const ScrollToBottomButton({super.key, required this.scrollController, required this.visibleValue});
+  final ValueNotifier<bool> visibleValue;
+  final ScrollController scrollController;
+
+  Future<void> _navigateToBottom(BuildContext context) async {
+    scrollController.animateTo(0, duration: const Duration(milliseconds: 300), curve: Curves.easeIn);
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return ValueListenableBuilder<bool>(
+      builder: (BuildContext context, bool value, Widget? child) {
+        return (value && child != null) ? child : const SizedBox.shrink();
+      },
+      valueListenable: visibleValue,
+      // TODO: fix hardcoded values for size and style here
+      child: IconButton(
+        tooltip: "Scroll to bottom",
+        icon: const Icon(Icons.expand_circle_down_rounded),
+        iconSize: 40,
+        style: IconButton.styleFrom(foregroundColor: const HSLColor.fromAHSL(0.5,240,0.96,0.68).toColor()),
+        onPressed: () => _navigateToBottom(context)));
+  }
+}
 
 class MessageList extends StatefulWidget {
   const MessageList({super.key, required this.narrow});
@@ -109,6 +134,9 @@ class MessageList extends StatefulWidget {
 
 class _MessageListState extends State<MessageList> {
   MessageListView? model;
+  final ScrollController scrollController = ScrollController();
+
+  final ValueNotifier<bool> _scrollToBottomVisibleValue = ValueNotifier<bool>(false);
 
   @override
   void didChangeDependencies() {
@@ -161,7 +189,26 @@ class _MessageListState extends State<MessageList> {
           child: Center(
             child: ConstrainedBox(
               constraints: const BoxConstraints(maxWidth: 760),
-              child: _buildListView(context))))));
+              child: NotificationListener<ScrollEndNotification>(
+                onNotification: (scrollEnd) {
+                  final metrics = scrollEnd.metrics;
+                  if (metrics.atEdge && metrics.pixels == 0) {
+                    _scrollToBottomVisibleValue.value = false;
+                  } else {
+                    _scrollToBottomVisibleValue.value = true;
+                  }
+                  return true;
+                },
+                child: Stack(
+                  children: <Widget>[
+                    _buildListView(context),
+                    Container(
+                      alignment: Alignment.bottomRight,
+                      child: ScrollToBottomButton(scrollController: scrollController, visibleValue: _scrollToBottomVisibleValue),
+                    ),
+                  ]
+                ),
+              ))))));
   }
 
   Widget _buildListView(context) {
@@ -179,6 +226,7 @@ class _MessageListState extends State<MessageList> {
         _ => ScrollViewKeyboardDismissBehavior.manual,
       },
 
+      controller: scrollController,
       itemCount: length,
       // Setting reverse: true means the scroll starts at the bottom.
       // Flipping the indexes (in itemBuilder) means the start/bottom