Flutter - calling setState() before the build - flutter

Question

I use a futureBuilder to display date inside TextFormFields, if there is data in the webservice I call in the futureBuilder for the date I selected in the DateTimePicker, the TextFormField is disabled and the data is displayed in it. Else, the textFormField is enabled.
I also have a button that I want to disable if there is data received and enable if there isn't, so I used a boolean.
Here is my code :
child: FutureBuilder<double?>(
future: getTimes(selectedDate),
builder: (BuildContext context, AsyncSnapshot snapshot) {
if (snapshot.hasData){
_timeController.clear();
setState(() {
_isButtonDisabled = false;
});
return TextFormField(
controller: _timeController,
textAlign: TextAlign.center,
enabled: false,
decoration: InputDecoration(
hintText: snapshot.data.toString() + " h",
contentPadding: EdgeInsets.zero,
filled: true,
fillColor: Colors.white70
),
);
}
else {
setState(() {
_isButtonDisabled = true;
});
return TextFormField(
controller: _timeController,
textAlign: TextAlign.center,
enabled: true,
decoration: InputDecoration(
hintText: "0 h",
contentPadding: EdgeInsets.zero,
filled: true,
fillColor: Colors.white
),
);
}
}
)
This was causing me the error setState() or markNeedsBuild called during build , so thanks to the answers of this topic I encapsulated the setState method in WidgetsBinding.instance.addPostFrameCallback((_)
Here is what my code looks like now :
child: FutureBuilder<double?>(
future: getTimes(selectedDate),
builder: (BuildContext context, AsyncSnapshot snapshot) {
if (snapshot.hasData){
_timeController.clear();
WidgetsBinding.instance?.addPostFrameCallback((_){
setState(() {
_isButtonDisabled = false;
});
});
return TextFormField(
controller: _timeController,
textAlign: TextAlign.center,
enabled: false,
decoration: InputDecoration(
hintText: snapshot.data.toString() + " h",
contentPadding: EdgeInsets.zero,
filled: true,
fillColor: Colors.white70
),
);
}
else {
WidgetsBinding.instance?.addPostFrameCallback((_){
setState(() {
_isButtonDisabled = true;
});
});
return TextFormField(
controller: _timeController,
textAlign: TextAlign.center,
enabled: true,
decoration: InputDecoration(
hintText: "0 h",
contentPadding: EdgeInsets.zero,
filled: true,
fillColor: Colors.white
),
);
}
}
)
The problem that I have now is my TextFormFields aren't clickable anymore, and the button is always enabled, may be a misused / misunderstood the addPostFrameCallback function.
Thanks for helping,

Answer 1

You have DateTimePicker, after the selecting date-time you can call the future.
getTimes() returns nullable double. Before retuning data, compare value is null or not and set _isButtonDisabled based on it, assign true/false.
bool _isButtonDisabled = true; // set the intial/watting state you want
Future<double?> getTimes(DateTime time) async {
//heavy operations
return await Future.delayed(Duration(seconds: 3), () {
return 4; //check with null +value
});
}
----
#override
Widget build(BuildContext context) {
print("rebuild");
return Column(
children: [
ElevatedButton(
onPressed: () async {
final selectedDate = await showDatePicker(
context: context,
initialDate: DateTime.now(),
firstDate: DateTime.now().subtract(Duration(days: 4444)),
lastDate: DateTime.now().add(Duration(days: 4444)),
);
if (selectedDate == null) return;
final response = await getTimes(selectedDate);
print(response);
setState(() {
_isButtonDisabled = response != null;
});
},
child: Text("Select Date"),
),
ElevatedButton(
onPressed: _isButtonDisabled ? null : () {}, child: Text("t"))
],
);}