refact: flutter, ChangeNotifier, reduce rebuild (#9392)

Signed-off-by: fufesou <linlong1266@gmail.com>

flutter/lib/common/widgets/peer_card.dart

@@ -250,6 +250,9 @@ class _PeerCardState extends State<_PeerCard>
       color: Colors.transparent,
       elevation: 0,
       margin: EdgeInsets.zero,
+      // to-do: memory leak here, more investigation needed.
+      // Continious rebuilds of `Obx()` will cause memory leak here.
+      // The simple demo does not have this issue.
       child: Obx(
         () => Container(
           foregroundDecoration: deco.value,

flutter/lib/common/widgets/peer_tab_page.dart

@@ -108,7 +108,7 @@ class _PeerTabPageState extends State<PeerTabPage>
   Widget build(BuildContext context) {
     final model = Provider.of<PeerTabModel>(context);
     Widget selectionWrap(Widget widget) {
-      return model.multiSelectionMode ? createMultiSelectionBar() : widget;
+      return model.multiSelectionMode ? createMultiSelectionBar(model) : widget;
     }
 
     return Column(
@@ -362,8 +362,7 @@ class _PeerTabPageState extends State<PeerTabPage>
             .toList());
   }
 
-  Widget createMultiSelectionBar() {
-    final model = Provider.of<PeerTabModel>(context);
+  Widget createMultiSelectionBar(PeerTabModel model) {
     return Row(
       mainAxisAlignment: MainAxisAlignment.spaceBetween,
       children: [
@@ -381,7 +380,7 @@ class _PeerTabPageState extends State<PeerTabPage>
         Row(
           children: [
             selectionCount(model.selectedPeers.length),
-            selectAll(),
+            selectAll(model),
             closeSelection(),
           ],
         )
@@ -512,8 +511,7 @@ class _PeerTabPageState extends State<PeerTabPage>
     );
   }
 
-  Widget selectAll() {
-    final model = Provider.of<PeerTabModel>(context);
+  Widget selectAll(PeerTabModel model) {
     return Offstage(
       offstage:
           model.selectedPeers.length >= model.currentTabCachedPeers.length,

flutter/lib/common/widgets/peers_view.dart

@@ -167,6 +167,9 @@ class _PeersViewState extends State<_PeersView>
 
   @override
   Widget build(BuildContext context) {
+    // We should avoid too many rebuilds. MacOS(m1, 14.6.1) on Flutter 3.19.6.
+    // Continious rebuilds of `ChangeNotifierProvider` will cause memory leak.
+    // Simple demo can reproduce this issue.
     return ChangeNotifierProvider<Peers>(
       create: (context) => widget.peers,
       child: Consumer<Peers>(builder: (context, peers, child) {
@@ -245,6 +248,9 @@ class _PeersViewState extends State<_PeersView>
                   : Container(child: visibilityChild);
             }
 
+            // We should avoid too many rebuilds. Win10(Some machines) on Flutter 3.19.6.
+            // Continious rebuilds of `ListView.builder` will cause memory leak.
+            // Simple demo can reproduce this issue.
             final Widget child = Obx(() => stateGlobal.isPortrait.isTrue
                 ? ListView.builder(
                     itemCount: peers.length,

flutter/lib/models/peer_tab_model.dart

@@ -184,10 +184,17 @@ class PeerTabModel with ChangeNotifier {
     notifyListeners();
   }
 
+  // `notifyListeners()` will cause many rebuilds.
+  // So, we need to reduce the calls to "notifyListeners()" only when necessary.
+  // A better way is to use a new model.
   setCurrentTabCachedPeers(List<Peer> peers) {
     Future.delayed(Duration.zero, () {
+      final isPreEmpty = _currentTabCachedPeers.isEmpty;
       _currentTabCachedPeers = peers;
-      notifyListeners();
+      final isNowEmpty = _currentTabCachedPeers.isEmpty;
+      if (isPreEmpty != isNowEmpty) {
+        notifyListeners();
+      }
     });
   }