Show value of dropdown with empty value at the beginning - flutter

Question

I would like that in my dropdown at the beginning no value is entered. only if I select the value it should be displayed in the dropdown. if I comment out "value: _selected" is not filled but after the onChanged also nothing is filled.
FormField<Device>(
initialValue: _selected,
builder: (field) {
return InputDecorator(
decoration: InputDecoration(
labelText: widget.labelText,
border: const OutlineInputBorder(),
),
child: DropdownButtonHideUnderline(
child: DropdownButton<Device>(
value: _selected,
isDense: true,
isExpanded: true,
items: widget.list
.map<DropdownMenuItem<Device>>((Device value) {
return DropdownMenuItem<Device>(
value: value,
child:
Text('${value.inventarnr} - ID: ${value.id}'),
);
}).toList(),
onChanged: (value) {
setState(() {
_selected = value;
});
},
),
),
);
},
),

Answer 1

Below worked example for your reference.
initializing default dropdown value
String phaseInitialValue = "Select dropdown";
declare a class to get the user selected value from dropdown.
I have using temporary json data...
List<Phase> phaseList = phaseJsonList.phaseList;
Phase phase = Phase("","");
FormField full code :
FormField(
initialValue: phaseInitialValue,
builder: (field) {
return InputDecorator(
decoration: const InputDecoration(
labelText: "Dropdown",
border: OutlineInputBorder(),
),
child: DropdownButtonHideUnderline(
child: DropdownButton(
hint: Text(
phaseInitialValue,
style: const TextStyle(
fontWeight: FontWeight.w400,
color: Color.fromRGBO(179, 179, 179, 1.0),
fontSize: 15.0,
fontStyle: FontStyle.normal
),
),
isExpanded: true,
iconSize: 30.0,
iconEnabledColor:
const Color.fromRGBO(0, 0, 0, 1.0),
style: const TextStyle(
color: Color.fromRGBO(0, 0, 0, 1)),
dropdownColor:
const Color.fromRGBO(255, 255, 255, 1.0),
borderRadius: BorderRadius.circular(5),
items: phaseList.map(
(phaseData) {
return DropdownMenuItem<Phase>(
value: phaseData,
child: Text(phaseData.phaseName),
);
},
).toList(),
onChanged: (Phase? newData) {
setState(() {
phase = newData!;
phaseInitialValue = newData.phaseName!;
},
);
},
),
),
);
},
),
if user changed the value from dropdown i have retrieve that from onChanged property. there i changed inital text to user selected object...
you can able to fetch actual id as well as object...
have a good day!!!