Add create accessor factory constructor

lib/src/value_accessors/control_value_accessor.dart

@@ -7,13 +7,31 @@ import 'dart:async';
 import 'package:flutter/foundation.dart';
 import 'package:reactive_forms/reactive_forms.dart';
 
+typedef _ModelToViewValueCallback<ModelDataType, ViewDataType> = ViewDataType?
+    Function(ModelDataType? modelValue);
+
+typedef _ViewToModelValueCallback<ModelDataType, ViewDataType> = ModelDataType?
+    Function(ViewDataType? modelValue);
+
 /// Type of the function to be called when the control emits a value changes
 /// event.
 typedef ChangeFunction<K> = dynamic Function(K? value);
 
 /// Defines an interface that acts as a bridge between [FormControl] and a
 /// reactive native widget.
 abstract class ControlValueAccessor<ModelDataType, ViewDataType> {
+  ControlValueAccessor();
+
+  /// Create simple [ControlValueAccessor] that maps the [FormControl] value
+  factory ControlValueAccessor.create({
+    _ModelToViewValueCallback<ModelDataType, ViewDataType>? modelToView,
+    _ViewToModelValueCallback<ModelDataType, ViewDataType>? valueToModel,
+  }) =>
+      _WrapperValueAccessor<ModelDataType, ViewDataType>(
+        modelToViewValue: modelToView,
+        valueToModelValue: valueToModel,
+      );
+
   FormControl<ModelDataType>? _control;
   ChangeFunction<ViewDataType>? _onChange;
   bool _viewToModelChange = false;
@@ -91,3 +109,33 @@ abstract class ControlValueAccessor<ModelDataType, ViewDataType> {
     }
   }
 }
+
+class _WrapperValueAccessor<ModelDataType, ViewDataType>
+    extends ControlValueAccessor<ModelDataType, ViewDataType> {
+  final _ModelToViewValueCallback<ModelDataType, ViewDataType>?
+      _modelToViewValue;
+  final _ViewToModelValueCallback<ModelDataType, ViewDataType>?
+      _valueToModelValue;
+
+  _WrapperValueAccessor({
+    _ModelToViewValueCallback<ModelDataType, ViewDataType>? modelToViewValue,
+    _ViewToModelValueCallback<ModelDataType, ViewDataType>? valueToModelValue,
+  })  : _modelToViewValue = modelToViewValue,
+        _valueToModelValue = valueToModelValue;
+
+  @override
+  ViewDataType? modelToViewValue(ModelDataType? modelValue) {
+    if (_modelToViewValue != null && modelValue != null) {
+      return _modelToViewValue!.call(modelValue);
+    }
+    return null;
+  }
+
+  @override
+  ModelDataType? viewToModelValue(ViewDataType? viewValue) {
+    if (_valueToModelValue != null) {
+      return _valueToModelValue?.call(viewValue);
+    }
+    return control?.value;
+  }
+}