start date and end date validation in Flutter - flutter

Question

In the below code I need to put validation like if the startdate is null give error to user or display the date chosen. I'm not sure how to do it.
String _displayText(String begin, DateTime? date) {
if (date != null) {
return '$begin Date: ${date.toString().split(' ')[0]}';
} else {
return 'Choose The Date';
}
}
In the below it will display the date
Text(
_displayText('Start', startdate),
style: const TextStyle(
fontWeight: FontWeight.bold, fontSize: 15, color: Colors.black),
),

Answer 1

To validate the date, we are checking the date and controlling validator using date not text. Like
String? endDateValidator(value) {
if (startDate != null && endData == null) {
return "select Both data";
}
if (endData == null) return "select the date";
if (endData!.isBefore(startDate!)) {
return "End date must be after startDate";
}
return null; // optional while already return type is null
}
Inside the form TextFormFiled will be
TextFormField(
controller: endDateController,
readOnly: true,
decoration: const InputDecoration(
hintText: 'Choose The Date',
),
onTap: () async {
endData = await pickDate();
endDateController.text = _displayText("start", endData);
setState(() {});
},
validator: endDateValidator,
),
Test on DartPad.
Widget to play
class DateValidationInForm extends StatefulWidget {
DateValidationInForm({Key? key}) : super(key: key);
#override
State<DateValidationInForm> createState() => _DateValidationInFormState();
}
class _DateValidationInFormState extends State<DateValidationInForm> {
/// more about validation https://docs.flutter.dev/cookbook/forms/validation
final _formKey = GlobalKey<FormState>();
String _displayText(String begin, DateTime? date) {
if (date != null) {
return '$begin Date: ${date.toString().split(' ')[0]}';
} else {
return 'Choose The Date';
}
}
final TextEditingController startDateController = TextEditingController(),
endDateController = TextEditingController();
DateTime? startDate, endData;
Future<DateTime?> pickDate() async {
return await showDatePicker(
context: context,
initialDate: DateTime.now(),
firstDate: DateTime(1999),
lastDate: DateTime(2999),
);
}
String? startDateValidator(value) {
if (startDate == null) return "select the date";
}
String? endDateValidator(value) {
if (startDate != null && endData == null) {
return "select Both data";
}
if (endData == null) return "select the date";
if (endData!.isBefore(startDate!)) {
return "End date must be after startDate";
}
return null; // optional while already return type is null
}
#override
Widget build(BuildContext context) {
return Form(
key: _formKey,
child: Column(
children: [
TextFormField(
controller: startDateController,
decoration: const InputDecoration(
hintText: 'Choose The Date',
),
onTap: () async {
startDate = await pickDate();
startDateController.text = _displayText("start", startDate);
setState(() {});
},
readOnly: true,
validator: startDateValidator,
style: const TextStyle(
fontWeight: FontWeight.bold, fontSize: 15, color: Colors.black),
),
TextFormField(
controller: endDateController,
readOnly: true,
decoration: const InputDecoration(
hintText: 'Choose The Date',
),
onTap: () async {
endData = await pickDate();
endDateController.text = _displayText("start", endData);
setState(() {});
},
validator: endDateValidator,
style: const TextStyle(
fontWeight: FontWeight.bold, fontSize: 15, color: Colors.black),
),
ElevatedButton(
onPressed: () {
_formKey.currentState?.validate();
},
child: Text("submit"),
)
],
),
);
}
}
Check cookbook/forms/validation to learn more.