fix transformers

Author: ahmednfwela

packages/flutter_form_builder/lib/src/form_builder.dart

@@ -92,7 +92,8 @@ class FormBuilderState extends State<FormBuilder> {
 
   final _fields = <String, FormBuilderFieldState>{};
 
-  final _transformers = <String, dynamic Function(dynamic)>{};
+  //because dart type system will not accept ValueTransformer<dynamic>
+  final _transformers = <String, Function>{};
   final _instantValue = <String, dynamic>{};
   final _savedValue = <String, dynamic>{};
 
@@ -162,9 +163,7 @@ class FormBuilderState extends State<FormBuilder> {
     }());
 
     _fields[name] = field;
-    if (field.widget.valueTransformer != null) {
-      _transformers[name] = field.widget.valueTransformer!;
-    }
+    field.registerTransformer(_transformers);
     if (oldField != null) {
       // ignore: invalid_use_of_protected_member
       field.setValue(

packages/flutter_form_builder/lib/src/form_builder_field.dart

@@ -74,8 +74,6 @@ class FormBuilderField<T> extends FormField<T> {
           validator: validator,
         );
 
-  /*@override
-  FormBuilderFieldState<T> createState();*/
   @override
   FormBuilderFieldState<FormBuilderField<T>, T> createState() =>
       FormBuilderFieldState<FormBuilderField<T>, T>();
@@ -102,6 +100,13 @@ class FormBuilderFieldState<F extends FormBuilderField<T>, T>
 
   dynamic get transformedValue => widget.valueTransformer?.call(value) ?? value;
 
+  void registerTransformer(Map<String, Function> _map) {
+    final _fun = widget.valueTransformer;
+    if (_fun != null) {
+      _map[widget.name] = _fun;
+    }
+  }
+
   @override
   String? get errorText => super.errorText ?? _customErrorText;