DropDownButton items in a variable - flutter

Question

I'm trying to store the possible values for a DropDownButton in a variable.
Goal:
On the press of a button, I want a new list of Strings to be created and assigned as possible choices for the DropdownButton. To do so, I need to store the possible choices (list of DropdownMenuItem) in a variable.
This sample of code works:
static String defaultDropDownValue = 'Select your Network';
String dropdownValue = defaultDropDownValue;
[...]
new Flexible(
child: DropdownButton(
isExpanded: true,
value: dropdownValue,
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
});
_checkSsid();
},
items: <String>[defaultDropDownValue, 'One', 'Two', 'Three', 'Four']
.map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList(),
),
),
[...]
Now, this sample of code does not work:
static String defaultDropDownValue = 'Select your Network';
String dropdownValue = defaultDropDownValue;
List<DropdownMenuItem> dropdownList = [defaultDropDownValue, 'one', 'two'].map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList();
[...]
new Flexible(
child: DropdownButton(
isExpanded: true,
value: dropdownValue,
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
});
_checkSsid();
},
items: dropdownList,
),
),
[...]
The compiler returns the following error message:
Error: The argument type 'Null Function(String)' can't be assigned to
the parameter type 'void Function(dynamic)'. Try changing the type of
the parameter, or casting the argument to 'void Function(dynamic)'.
onChanged: (String newValue) {
I don't really understand the meaning of the message, nor its cause.

Answer 1

Becasue you don't explicitly define the Type for array in the second example,
You could try DropdownMenuItem<String> and DropdownButton<String> to explicit them.
static String defaultDropDownValue = 'Select your Network';
String dropdownValue = defaultDropDownValue;
List<DropdownMenuItem<String>> dropdownList = [defaultDropDownValue, 'one', 'two'].map<DropdownMenuItem<String>>((String value) {
return DropdownMenuItem<String>(
value: value,
child: Text(value),
);
}).toList();
[...]
new Flexible(
child: DropdownButton<String>(
isExpanded: true,
value: dropdownValue,
onChanged: (String newValue) {
setState(() {
dropdownValue = newValue;
});
_checkSsid();
},
items: dropdownList,
),
),
[...]
Referenced from DropdownButton's Documentation below:
The type T is the type of the value that each dropdown item represents. All the entries in a given menu must represent values with consistent types. Typically, an enum is used. Each DropdownMenuItem in items must be specialized with that same type argument.