[State Restoration] RestorableBoolN (#71653)

packages/flutter/lib/src/widgets/restoration_properties.dart

@@ -143,19 +143,11 @@ abstract class RestorableValue<T> extends RestorableProperty<T> {
   void didUpdateValue(T? oldValue);
 }
 
-// _RestorablePrimitiveValue and its subclasses do not allow null values in
-// anticipation of NNBD (non-nullability by default).
-//
-// If necessary, we can in the future define a new subclass hierarchy that
-// does allow null values for primitive types. Borrowing from lisp where
-// functions that returned a bool ended in 'p', a suggested naming scheme for
-// these new subclasses could be to add 'N' (for nullable) to the end of a
-// class name (e.g. RestorableIntN, RestorableStringN, etc.) to distinguish them
-// from their non-nullable friends.
-class _RestorablePrimitiveValue<T extends Object> extends RestorableValue<T> {
-  _RestorablePrimitiveValue(this._defaultValue)
-    : assert(_defaultValue != null),
-      assert(debugIsSerializableForRestoration(_defaultValue)),
+// _RestorablePrimitiveValueN and its subclasses allows for null values.
+// See [_RestorablePrimitiveValue] for the non-nullable version of this class.
+class _RestorablePrimitiveValueN<T extends Object?> extends RestorableValue<T> {
+  _RestorablePrimitiveValueN(this._defaultValue)
+    : assert(debugIsSerializableForRestoration(_defaultValue)),
       super();
 
   final T _defaultValue;
@@ -163,28 +155,43 @@ class _RestorablePrimitiveValue<T extends Object> extends RestorableValue<T> {
   @override
   T createDefaultValue() => _defaultValue;
 
-  @override
-  set value(T value) {
-    assert(value != null);
-    super.value = value;
-  }
-
   @override
   void didUpdateValue(T? oldValue) {
     assert(debugIsSerializableForRestoration(value));
     notifyListeners();
   }
 
+  @override
+  T fromPrimitives(Object? serialized) => serialized as T;
+
+  @override
+  Object? toPrimitives() => value;
+}
+
+// _RestorablePrimitiveValue and its subclasses are non-nullable.
+// See [_RestorablePrimitiveValueN] for the nullable version of this class.
+class _RestorablePrimitiveValue<T extends Object> extends _RestorablePrimitiveValueN<T> {
+  _RestorablePrimitiveValue(T _defaultValue)
+    : assert(_defaultValue != null),
+      assert(debugIsSerializableForRestoration(_defaultValue)),
+      super(_defaultValue);
+
+  @override
+  set value(T value) {
+    assert(value != null);
+    super.value = value;
+  }
+
   @override
   T fromPrimitives(Object? serialized) {
     assert(serialized != null);
-    return serialized! as T;
+    return super.fromPrimitives(serialized);
   }
 
   @override
   Object toPrimitives() {
     assert(value != null);
-    return value;
+    return super.toPrimitives()!;
   }
 }
 
@@ -249,9 +256,28 @@ class RestorableBool extends _RestorablePrimitiveValue<bool> {
   /// Creates a [RestorableBool].
   ///
   /// {@macro flutter.widgets.RestorableNum.constructor}
+  ///
+  /// See also:
+  ///
+  ///  * [RestorableBoolN] for the nullable version of this class.
   RestorableBool(bool defaultValue) : assert(defaultValue != null), super(defaultValue);
 }
 
+/// A [RestorableProperty] that knows how to store and restore a [bool] that is
+/// nullable.
+///
+/// {@macro flutter.widgets.RestorableNum}
+class RestorableBoolN extends _RestorablePrimitiveValueN<bool?> {
+  /// Creates a [RestorableBoolN].
+  ///
+  /// {@macro flutter.widgets.RestorableNum.constructor}
+  ///
+  /// See also:
+  ///
+  ///  * [RestorableBool] for the non-nullable version of this class.
+  RestorableBoolN(bool? defaultValue) : super(defaultValue);
+}
+
 /// A base class for creating a [RestorableProperty] that stores and restores a
 /// [Listenable].
 ///
@@ -313,17 +339,17 @@ abstract class RestorableListenable<T extends Listenable> extends RestorableProp
 abstract class RestorableChangeNotifier<T extends ChangeNotifier> extends RestorableListenable<T> {
   @override
   void initWithValue(T value) {
-    _diposeOldValue();
+    _disposeOldValue();
     super.initWithValue(value);
   }
 
   @override
   void dispose() {
-    _diposeOldValue();
+    _disposeOldValue();
     super.dispose();
   }
 
-  void _diposeOldValue() {
+  void _disposeOldValue() {
     if (_value != null) {
       // Scheduling a microtask for dispose to give other entities a chance
       // to remove their listeners first.

packages/flutter/test/widgets/restorable_property_test.dart

@@ -13,6 +13,7 @@ void main() {
     expect(() => RestorableInt(1).value, throwsAssertionError);
     expect(() => RestorableString('hello').value, throwsAssertionError);
     expect(() => RestorableBool(true).value, throwsAssertionError);
+    expect(() => RestorableBoolN(true).value, throwsAssertionError);
     expect(() => RestorableTextEditingController().value, throwsAssertionError);
     expect(() => _TestRestorableValue().value, throwsAssertionError);
   });
@@ -125,6 +126,7 @@ void main() {
       state.intValue.value = 10;
       state.stringValue.value = 'guten tag';
       state.boolValue.value = true;
+      state.nullableBoolValue.value = false;
       state.controllerValue.value.text = 'blabla';
       state.objectValue.value = 53;
     });
@@ -140,6 +142,7 @@ void main() {
       state.intValue.value = 20;
       state.stringValue.value = 'ciao';
       state.boolValue.value = false;
+      state.nullableBoolValue.value = null;
       state.controllerValue.value.text = 'blub';
       state.objectValue.value = 20;
     });
@@ -154,6 +157,7 @@ void main() {
     expect(state.intValue.value, 10);
     expect(state.stringValue.value, 'guten tag');
     expect(state.boolValue.value, true);
+    expect(state.nullableBoolValue.value, false);
     expect(state.controllerValue.value.text, 'blabla');
     expect(state.objectValue.value, 53);
     expect(find.text('guten tag'), findsOneWidget);
@@ -166,6 +170,7 @@ void main() {
     expect(state.intValue.value, 42);
     expect(state.stringValue.value, 'hello world');
     expect(state.boolValue.value, false);
+    expect(state.nullableBoolValue.value, null);
     expect(state.controllerValue.value.text, 'FooBar');
     expect(state.objectValue.value, 55);
     expect(find.text('hello world'), findsOneWidget);
@@ -323,6 +328,7 @@ class _RestorableWidgetState extends State<_RestorableWidget> with RestorationMi
   final RestorableInt intValue = RestorableInt(42);
   final RestorableString stringValue = RestorableString('hello world');
   final RestorableBool boolValue = RestorableBool(false);
+  final RestorableBoolN nullableBoolValue = RestorableBoolN(null);
   final RestorableTextEditingController controllerValue = RestorableTextEditingController(text: 'FooBar');
   final _TestRestorableValue objectValue = _TestRestorableValue();
 
@@ -332,7 +338,8 @@ class _RestorableWidgetState extends State<_RestorableWidget> with RestorationMi
     registerForRestoration(doubleValue, 'double');
     registerForRestoration(intValue, 'int');
     registerForRestoration(stringValue, 'string');
-    registerForRestoration(boolValue,'bool');
+    registerForRestoration(boolValue, 'bool');
+    registerForRestoration(nullableBoolValue, 'nullableBool');
     registerForRestoration(controllerValue, 'controller');
     registerForRestoration(objectValue, 'object');
   }