Add method

README.md

@@ -62,6 +62,20 @@ Now whenever `counter.value` changes (here using `counter.value++` in the `onPre
 
 That's all there is to it!
 
+## Notifying listeners of deeper changes
+
+If you try to wrap a collection or object in a `ValueNotifier`, e.g. to track a set of values using `ValueNotifier<Set<T>>`, then modifying fields, or adding or removing values from the collection or object will not notify the listeners of the `ValueNotifier` that the value has changed (because the value itself has not changed). In this case you can call the extension method `notifyChanged()` to manually call the listeners. For example:
+
+```dart
+final tags = ValueNotifier(<String>{});
+
+void addOrRemoveTag(String tag, bool add) {
+  if ((add && tags.value.add(tag)) || (!add && tags.value.remove(tag))) {
+    tags.notifyChanged();
+  }
+}
+```
+
 ## The code
 
 The `flutter_reactive_value` mechanism is extremely simple. [See the code here.](https://github.com/lukehutch/flutter_reactive_value/blob/main/lib/src/reactive_value_notifier.dart)

lib/src/reactive_value_notifier.dart

@@ -5,7 +5,12 @@ class _ListenerWrapper<T> {
   void Function()? listener;
 }
 
+/// Extend [ValueNotifier] so that [Element] objects in the build tree can
+/// respond to changes in the value.
 extension ReactiveValueNotifier<T> on ValueNotifier<T> {
+  /// Fetch the [value] of this [ValueNotifier], and subscribe the element
+  /// that is currently being built (the [context]) to any changes in the
+  /// value.
   T reactiveValue(BuildContext context) {
     final elementRef = WeakReference(context as Element);
     // Can't refer to listener while it is being declared, so need to add
@@ -29,4 +34,12 @@ extension ReactiveValueNotifier<T> on ValueNotifier<T> {
     addListener(listenerWrapper.listener!);
     return value;
   }
+
+  /// Use this method to notify listeners of deeper changes, e.g. when a value
+  /// is added to or removed from a set which is stored in the value of a
+  /// `ValueNotifier<Set<T>>`.
+  void notifyChanged() {
+    // ignore: invalid_use_of_protected_member, invalid_use_of_visible_for_testing_member
+    notifyListeners();
+  }
 }