Add scroll down button in chat

CHANGELOG.md

@@ -2,6 +2,7 @@
 ### New features
 - Select mode in chat
 - Implement replies
+- Add scroll down button in chat
 
 # Version 0.6.0 - 2020-02-09
 ### New features

lib/views/chat.dart

@@ -70,6 +70,8 @@ class _ChatState extends State<_Chat> {
 
   Event replyEvent;
 
+  bool showScrollDownButton = false;
+
   bool get selectMode => selectedEvents.isNotEmpty;
 
   @override
@@ -82,6 +84,13 @@ class _ChatState extends State<_Chat> {
               EventTypes.RoomCreate) {
         await timeline.requestHistory(historyCount: 100);
       }
+      if (_scrollController.position.pixels > 0 &&
+          showScrollDownButton == false) {
+        setState(() => showScrollDownButton = true);
+      } else if (_scrollController.position.pixels == 0 &&
+          showScrollDownButton == true) {
+        setState(() => showScrollDownButton = false);
+      }
     });
 
     super.initState();
@@ -366,6 +375,18 @@ class _ChatState extends State<_Chat> {
               ]
             : <Widget>[ChatSettingsPopupMenu(room, !room.isDirectChat)],
       ),
+      floatingActionButton: showScrollDownButton
+          ? Padding(
+              padding: const EdgeInsets.only(bottom: 56.0),
+              child: FloatingActionButton(
+                child: Icon(Icons.arrow_downward,
+                    color: Theme.of(context).primaryColor),
+                onPressed: () => _scrollController.jumpTo(0),
+                backgroundColor: Theme.of(context).scaffoldBackgroundColor,
+                mini: true,
+              ),
+            )
+          : null,
       body: SafeArea(
         child: Column(
           children: <Widget>[