fix datepicker

com.unity.uiwidgets/Runtime/cupertino/date_picker.cs

                     _onSelectedItemChange(index); 
                 },
                 itemBuilder: (BuildContext context, int index) => {
-                    var startDay = initialDateTime.Day + index;
+                    
-                        day:startDay
+                        day:initialDateTime.Day
+                    rangeStart.AddDays(index);
                     
                     var rangeEnd  = rangeStart.AddDays(1);
                     

com.unity.uiwidgets/Runtime/widgets/framework.cs

             D.assert(!_debugBuilding);
             D.assert(() => {
                 if (WidgetsD.debugPrintBuildScope) {
-                    Debug.LogFormat("buildScope called with context {0}; dirty list is: {1}",
-                        context, _dirtyElements);
+                    Debug.LogFormat($"buildScope called with context {context}; dirty list is: {_dirtyElements}");
-
                 _debugStateLockLevel += 1;
                 _debugBuilding = true;
                 return true;
                         debugPreviousBuildTarget = _debugCurrentBuildTarget;
                         _debugCurrentBuildTarget = context;
                         return true;
-                    });
-
+                    }); 
-
                     try {
                         callback();
                     }

com.unity.uiwidgets/Runtime/widgets/list_wheel_scroll_view.cs

         public void createChild(int index, RenderBox after) {
             owner.buildScope(this, () => {
                 bool insertFirst = after == null;
-                D.assert(insertFirst || _childElements[index - 1] != null);
+                D.assert(insertFirst || _childElements.getOrDefault(index - 1) != null);
                 Element newChild = updateChild(_childElements.getOrDefault(index), retrieveWidget(index), index);
                 if (newChild != null) {
                     _childElements[index] = newChild;