bug fix on material datetime picker widget

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/demo/material/date_and_time_picker_demo.cs

             this.labelText = labelText;
             this.selectDate = selectDate;
             this.selectedTime = selectedTime;
-            this.selectDate = selectDate;
+            this.selectedDate = selectedDate;
             this.selectTime = selectTime;
         }
 
             material_.showDatePicker(
                 context: context,
                 initialDate: this.selectedDate.Value,
-                firstDate: new DateTime(2015, 8, 0),
-                lastDate: new DateTime(2101, 0, 0)
+                firstDate: new DateTime(2015, 8, 1),
+                lastDate: new DateTime(2030, 1, 1)
             ).then((object value) =>
             {
                 var picked = (DateTime) value;

Samples/UIWidgetsSamples_2019_4/Assets/UIWidgetsGallery/gallery/demos.cs

                     buildRoute: (BuildContext context) => new PageSelectorDemo()
                 ),
                 new GalleryDemo(
+                    title: "Pickers",
+                    subtitle: "Date and time selection widgets",
+                    icon: GalleryIcons.events,
+                category: GalleryDemoCategory._kMaterialComponents,
+                routeName: DateAndTimePickerDemo.routeName,
+                documentationUrl: "https://docs.flutter.io/flutter/material/showDatePicker.html",
+                buildRoute: (BuildContext context) => new DateAndTimePickerDemo()
+                ),
+                new GalleryDemo(
                     title: "Progress indicators",
                     subtitle: "Linear, circular, indeterminate",
                     icon: GalleryIcons.progress_activity,

com.unity.uiwidgets/Runtime/material/pickers/calendar_date_picker.cs

             for (int i = localizations.firstDayOfWeekIndex; true; i = (i + 1) % 7) {
                 string weekday = localizations.narrowWeekdays[i];
                 result.Add(new Center(child: new Text(weekday, style: headerStyle)));
-                if (i == (localizations.firstDayOfWeekIndex - 1) % 7)
+                if (i == (localizations.firstDayOfWeekIndex - 1 + 7) % 7)
                     break;
             }
 

com.unity.uiwidgets/Runtime/material/pickers/date_utils.cs

         }
 
         public static DateTime addMonthsToMonthDate(DateTime monthDate, int monthsToAdd) {
-            return new DateTime(monthDate.Year, monthDate.Month + monthsToAdd, 1);
+            return monthDate.AddMonths(monthsToAdd);
         }
 
         public static int firstDayOffset(int year, int month, MaterialLocalizations localizations) {

com.unity.uiwidgets/Runtime/material/pickers/input_date_picker.cs

 
         public readonly WhitelistingTextInputFormatter _filterFormatter =
             // Only allow digits and separators (slash, dot, comma, hyphen, space).
-            new WhitelistingTextInputFormatter(new Regex(@"[\d\/\.,-\s]+"));
+            new WhitelistingTextInputFormatter(new Regex(@"[\d\/\.,\- ]+"));
 
         public override TextEditingValue formatEditUpdate(TextEditingValue oldValue, TextEditingValue newValue) {
             TextEditingValue filteredValue = _filterFormatter.formatEditUpdate(oldValue, newValue);

com.unity.uiwidgets/Runtime/material/time_picker.cs

                 if (fragmentContext.use24HourDials) {
                     int selectedHour = fragmentContext.selectedTime.hour;
                     return fragmentContext.selectedTime.replacing(
-                        hour: (selectedHour + hoursToAdd) % TimeOfDay.hoursPerDay
+                        hour: (selectedHour + hoursToAdd + TimeOfDay.hoursPerDay) % TimeOfDay.hoursPerDay
                     );
                 }
                 else {
-                        hour: periodOffset + (hours + hoursToAdd) % TimeOfDay.hoursPerPeriod
+                        hour: (periodOffset + (hours + hoursToAdd) + TimeOfDay.hoursPerPeriod) % TimeOfDay.hoursPerPeriod
                     );
                 }
             }