value protected for vm

lib/src/implements/notifier_impl.dart

@@ -1,15 +1,16 @@
 import 'package:flutter/foundation.dart';
 
 @protected
-abstract class NotifierImpl<T> extends ChangeNotifier
-    implements ValueListenable<T> {
+/// value return.
+abstract class NotifierImpl<T> extends ChangeNotifier implements ValueListenable<T> {
   T _value;
   NotifierImpl(this._value) {
     if (kFlutterMemoryAllocationsEnabled) {
       ChangeNotifier.maybeDispatchObjectCreation(this);
     }
   }
 
+
   @override
   T get value => _value;
 
@@ -36,12 +37,40 @@ abstract class NotifierImpl<T> extends ChangeNotifier
   String toString() => '${describeIdentity(this)}($value)';
 }
 
-// abstract class ValueListenable<T> extends Listenable {
-//   /// Abstract const constructor. This constructor enables subclasses to provide
-//   /// const constructors so that they can be used in const expressions.
-//   const ValueListenable();
-//
-//   /// The current value of the object. When the value changes, the callbacks
-//   /// registered with [addListener] will be invoked.
-//   T get state;
-// }
+
+@protected
+abstract class StateNotifierImpl<T> extends ChangeNotifier implements ValueListenable<T> {
+  T _value;
+  StateNotifierImpl(this._value) {
+    if (kFlutterMemoryAllocationsEnabled) {
+      ChangeNotifier.maybeDispatchObjectCreation(this);
+    }
+  }
+
+
+  @protected
+  @override
+  T get value => _value;
+
+  /// [updateState]
+  /// Updates the state and notifies listeners if the value has changed.
+  ///
+  void updateState(T newState) {
+    if (_value == newState) {
+      return;
+    }
+
+    _value = newState;
+    notifyListeners();
+  }
+
+  /// [updateSilently]
+  /// Updates the value silently without notifying listeners.
+  ///
+  void updateSilently(T newState) {
+    _value = newState;
+  }
+
+  @override
+  String toString() => '${describeIdentity(this)}($value)';
+}