How to set initial default value in drop down flutter - flutter

Question

I've one drop down and there some value inside the drop-down button and I need to by default selected value. you can seel below piece of snippet where you can find the drop-down value. I need it always there is by default selected value Normal. hope you understand the question.
FormBuilder(
autovalidate: autovalidate,
child: FormBuilderCustomField(
attribute: "Select Address",
validators: [
FormBuilderValidators.required(),
],
formField: FormField(
builder: (FormFieldState<dynamic> field) {
return InputDecorator(
decoration: InputDecoration(
errorText: field.errorText,
filled: false,
isDense: true,
border: InputBorder.none,
icon: Container(
width: 50.0,
height: 50.0,
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(20.0),
color: colorStyles['primary_light'],
),
child: Icon(
Icons.business_center,
color: colorStyles['primary'],
),
),
),
isEmpty: _typeValue == [],
child: new DropdownButtonHideUnderline(
child: DropdownButton(
hint: Text("Service Type"),
isExpanded: true,
items: [
"normal",
"urgent",
"emergency",
].map((option) {
return DropdownMenuItem(
child: Text("$option"),
value: option,
);
}).toList(),
value: field.value,
onChanged: (value) {
field.didChange(value);
_serviceType = value;
},
),
),
);
},
)),
);

Answer 1

Just Asign on initState()
selectedDropDownValue = "normal";
In DropDown, asign selectedDropDownValue to value, and update on onChanged callback
new DropdownButtonHideUnderline(
child: DropdownButton(
hint: Text("Service Type"),
isExpanded: true,
items: [
"normal",
"urgent",
"emergency",
].map((option) {
return DropdownMenuItem(
child: Text("$option"),
value: option,
);
}).toList(),
value: selectedDropDownValue, //asign the selected value
onChanged: (value) {
setState((){
selectedDropDownValue = value; //on selection, selectedDropDownValue i sUpdated
});
},
),
),
);