Flutter : serState() or markNeedBuild() called during build - flutter

Question

I have a widget which used to select a date, at beginning it's with 'no date chosen', and the widget in a column below it depends on it [which mean its show a list of timeSlots of Data if I selected a date]
But I got a setState called during build error, and This ReservationSlotWidget can not be marked as needing to build because the Framework is already in the process of building widgets
This is the selectDate widget
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Row(
children: <Widget>[
Icon(
Icons.date_range,
color: Colors.white,
),
SizedBox(
width: 5,
),
Text(
_formatted == null
? 'No date chosen'
: _formatted,
style: TextStyle(
color: Colors.white,
))
],
),
FlatButton(
onPressed: ()=>_selectReservationDate(context),
child: Text(
'choose Date',
style: TextStyle(
color: Colors.white,
decoration: TextDecoration.underline),
),
)
],
),
if(_selectedDate != null)
Divider(
color: parseColor('#2A2E43'),
thickness: 2.0,
),
if(_selectedDate != null)
Row(
children: <Widget>[
Icon(
Icons.alarm,
color: Colors.white,
),
SizedBox(
width: 5,
),
Text('$_numberOfSeats Available Time Slots',
style: TextStyle(
color: Colors.white,
))
],
),
this is a listview items which appeared depend on the date I chose.
if(_formatted != null)
Expanded(
child: Consumer<SlotProvider>(
builder: (ctx, slotProvider, _)=>
ListView.builder(
itemCount: slotProvider.slots.length,
scrollDirection: Axis.horizontal,
itemBuilder: (ctx, index) {
setState(() {
_numberOfSeats = slotProvider.slots[index].seats;
});
return GestureDetector(
onTap: () {
setState(() {
if(_isInit){
_isExpanded = !_isExpanded;
}
_expandedIndex = index;
_isInit = false;
});
},
child: Container(
padding: EdgeInsets.all(4),
margin: EdgeInsets.all(4),
decoration: BoxDecoration(
color: _expandedIndex == index
? Theme.of(context).primaryColor
: parseColor('#2A2E43'),
borderRadius:
BorderRadius.all(Radius.circular(10))),
child: SlotsWidget(
fromTime: slotProvider.slots[index].fromTime.toString(),
toTime:slotProvider.slots[index].toTime.toString(),
seats:slotProvider.slots[index].seats,
))
);
}
),
)
),

Answer 1

the comment of #void is right and you can avoid the repeated setState with if block;
if (_numberOfSeats != slotProvider.slots[index].seats)
setState(() {
_numberOfSeats = slotProvider.slots[index].seats;
});