Working on message search+filter

flutter/lib/state/app_bar_state.dart

@@ -9,12 +9,37 @@ class AppBarState extends ChangeNotifier {
 
   AppBarState._internal() {}
 
+  List<void Function(String)> _searchListeners = [];
+
   bool _loadingIndeterminate = false;
   bool get loadingIndeterminate => _loadingIndeterminate;
 
+  bool _showSearchField = false;
+  bool get showSearchField => _showSearchField;
+
   void setLoadingIndeterminate(bool v) {
     if (_loadingIndeterminate == v) return;
     _loadingIndeterminate = v;
     notifyListeners();
   }
+
+  void setShowSearchField(bool v) {
+    if (_showSearchField == v) return;
+    _showSearchField = v;
+    notifyListeners();
+  }
+
+  void subscribeSearchListener(void Function(String) listener) {
+    _searchListeners.add(listener);
+  }
+
+  void unsubscribeSearchListener(void Function(String) listener) {
+    _searchListeners.remove(listener);
+  }
+
+  void notifySearchListeners(String query) {
+    for (var listener in _searchListeners) {
+      listener(query);
+    }
+  }
 }