DropdownButton is always disabled - flutter

Question

I'm putting a DropdownButton in a TileList's trailing, settings up the parameters shown in the docs to make it active, but It stays disabled regardless.
The ListTile is part of a ListView not included in the code below.
I set up setState() like the docs stated but no avail.
I am not able to find the root cause of this issue, no idea what's causing it.
I've tried enum with int as a value but it also didn't work.
...
final Store<AppState> store;
Units unit;
#override
void initState() {
super.initState();
unit = store.state.weatherState?.temperature?.unit;
}
...
enum Units {Celsius, Fahrenheit, Kelvin}
Widget _displayUnitsSettings({Store<AppState> store}) {
return ListTile(
dense: true,
enabled: true,
selected: true,
title: Text(
"Temperature Unit",
style: TextStyle(
decoration: TextDecoration.underline,
decorationStyle: TextDecorationStyle.dotted,
fontSize: 14,
fontWeight: FontWeight.w700,
color: Colors.white),
),
subtitle: Text(
"Default: Celsius.\nAvailable units: Celsius, Fahrenheit, Kelvin.",
style: TextStyle(
fontSize: 9, fontWeight: FontWeight.w700, color: Colors.white54),
),
trailing: DropdownButton(
style: TextStyle(
fontSize: 14, fontWeight: FontWeight.w700, color: Colors.white54),
isDense: true,
value: unit,
onChanged: (value) {
store.dispatch(ChangeUnit(unit: value));
setState(() {
unit = value;
});
},
items: <DropdownMenuItem>[
DropdownMenuItem(
value: Units.Celsius,
child: Text("Celsius"),
),
DropdownMenuItem(
value: Units.Fahrenheit,
child: Text("Fahrenheit"),
),
DropdownMenuItem(
value: Units.Kelvin,
child: Text("Kelvin"),
),
],
),
);
}
...
EDIT: The DropdownButton seem to be enabled but I am unable to click it.

Answer 1

Here's the problem. You have an AppBar with no position after the ListView on a Stack. What this mean is that the AppBar is overlapping over your ListView and therefore intercepting the gestures on your DropdownButton.
Wrap your AppBar with a Positioned widget and it will work. Like this:
Positioned(
top: 0.0,
left: 0.0,
right: 0.0,
child: AppBar(
leading: _backButton(context),
backgroundColor: Colors.transparent,
elevation: 0,
),
),