Add controller support

lib/src/field.dart

@@ -133,23 +133,20 @@ class DateTimeField extends StatelessWidget {
     }
 
     if (Theme.of(context).platform == TargetPlatform.iOS) {
-      final DateTime? _selectedDateTime =
+      final DateTime? _selectedDateTime = await showCupertinoPicker(context, initialDateTime);
-          await showCupertinoPicker(context, initialDateTime);
       if (_selectedDateTime != null) {
         onDateSelected!(_selectedDateTime);
       }
     } else {
       DateTime _selectedDateTime = initialDateTime;
 
-      const List<DateTimeFieldPickerMode> modesWithDate =
+      const List<DateTimeFieldPickerMode> modesWithDate = <DateTimeFieldPickerMode>[
-          <DateTimeFieldPickerMode>[
         DateTimeFieldPickerMode.dateAndTime,
         DateTimeFieldPickerMode.date
       ];
 
       if (modesWithDate.contains(mode)) {
-        final DateTime? _selectedDate =
+        final DateTime? _selectedDate = await showMaterialDatePicker(context, initialDateTime);
-            await showMaterialDatePicker(context, initialDateTime);
 
         if (_selectedDate != null) {
           _selectedDateTime = _selectedDate;
@@ -158,15 +155,13 @@ class DateTimeField extends StatelessWidget {
         }
       }
 
-      final List<DateTimeFieldPickerMode> modesWithTime =
+      final List<DateTimeFieldPickerMode> modesWithTime = <DateTimeFieldPickerMode>[
-          <DateTimeFieldPickerMode>[
         DateTimeFieldPickerMode.dateAndTime,
         DateTimeFieldPickerMode.time
       ];
 
       if (modesWithTime.contains(mode)) {
-        final TimeOfDay? _selectedTime = await showMaterialTimePicker(
+        final TimeOfDay? _selectedTime = await showMaterialTimePicker(context, initialDateTime,
-            context, initialDateTime,
             initialEntryMode: initialTimePickerEntryMode);
 
         if (_selectedTime != null) {
@@ -186,8 +181,7 @@ class DateTimeField extends StatelessWidget {
 
   /// Launches the Material time picker by invoking [showTimePicker].
   /// Can be @[override]n to allow further customization of the picker options
-  Future<TimeOfDay?> showMaterialTimePicker(
+  Future<TimeOfDay?> showMaterialTimePicker(BuildContext context, DateTime initialDateTime,
-      BuildContext context, DateTime initialDateTime,
       {TimePickerEntryMode initialEntryMode = TimePickerEntryMode.dial}) async {
     return showTimePicker(
       initialTime: TimeOfDay.fromDateTime(initialDateTime),
@@ -274,8 +268,7 @@ enum DateTimeFieldPickerMode { time, date, dateAndTime }
 /// Returns the [CupertinoDatePickerMode] corresponding to the selected
 /// [DateTimeFieldPickerMode]. This exists to prevent redundancy in the [DateTimeField]
 /// widget parameters.
-CupertinoDatePickerMode cupertinoModeFromPickerMode(
+CupertinoDatePickerMode cupertinoModeFromPickerMode(DateTimeFieldPickerMode mode) {
-    DateTimeFieldPickerMode mode) {
   switch (mode) {
     case DateTimeFieldPickerMode.time:
       return CupertinoDatePickerMode.time;

lib/src/form_field.dart

@@ -31,27 +31,37 @@ class DateTimeFormField extends FormField<DateTime> {
     DatePickerMode initialDatePickerMode = DatePickerMode.day,
     DateTimeFieldPickerMode mode = DateTimeFieldPickerMode.dateAndTime,
     TimePickerEntryMode initialTimePickerEntryMode = TimePickerEntryMode.dial,
+    DateTimeFormFieldController? controller,
     DateTimeFieldCreator fieldCreator = DateTimeField.new,
   }) : super(
           key: key,
-          initialValue: initialValue,
+          initialValue:
+              initialValue == null && controller != null ? controller.selectedDate : initialValue,
           onSaved: onSaved,
           validator: validator,
           autovalidateMode: autovalidateMode,
           enabled: enabled,
           builder: (FormFieldState<DateTime> field) {
+            if (controller != null) {
+              controller.addListener(() {
+                field.didChange(controller.selectedDate);
+              });
+            }
+
             // Theme defaults are applied inside the _InputDropdown widget
             final InputDecoration _decorationWithThemeDefaults =
                 decoration ?? const InputDecoration();
 
             final InputDecoration effectiveDecoration =
-                _decorationWithThemeDefaults.copyWith(
+                _decorationWithThemeDefaults.copyWith(errorText: field.errorText);
-                    errorText: field.errorText);
 
             void onChangedHandler(DateTime value) {
               if (onDateSelected != null) {
                 onDateSelected(value);
               }
+              if (controller != null) {
+                controller.selectedDate = value;
+              }
               field.didChange(value);
             }
 
@@ -77,3 +87,12 @@ class DateTimeFormField extends FormField<DateTime> {
   @override
   FormFieldState<DateTime> createState() => FormFieldState<DateTime>();
 }
+
+class DateTimeFormFieldController extends ChangeNotifier {
+  DateTime? _selectedDate;
+  DateTime? get selectedDate => _selectedDate;
+  set selectedDate(DateTime? value) {
+    _selectedDate = value;
+    notifyListeners();
+  }
+}