创建一个州、城市下拉列表，根据所选州显示城市下拉的值?

Question

创建一个州，城市下拉列表，根据所选状态，API 请求将触发并将响应显示为城市下拉列表的值，对此有什么想法吗？

Answer 1

您可以按以下方式使用下拉列表来实现您的期望。

import 'package:flutter/material.dart';
class DropDown extends StatefulWidget {
@override
_DropDownState createState() => _DropDownState();
}
class _DropDownState extends State<DropDown> {

Map<String, String> stateCity = {
"Surat": "Gujarat",
"Ahmadabad": "Gujarat",
"Vadodara": "Gujarat",
"Mp1": "Mp",
"Mp2": "Mp",
"Up1": "Up",
"Up2": "Up",
"Up3": "Up",
};
List<String> state = ['Gujarat','Mp','Up'];
List<String>  city= [];
String selectedState;
String selectedcity;
@override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
child: Center(
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
DropdownButton(
onChanged: (value) {
setState(() {
selectedState = value;
selectedcity =null;
city.clear();
stateCity.forEach((k,v){
print(k);
if(selectedState==v){
city.add(k);
}
});
});
},
value: selectedState,
items: state
.map((state) => DropdownMenuItem(
child: Text(state),
value: state,
))
.toList(),
),
DropdownButton(
onChanged: (value) {
setState(() {
selectedcity = value;
});
print(value);
},
value: selectedcity,
items: selectedState !=  null ? city.map((city) => DropdownMenuItem(child: Text(city),value: city,)).toList(): [],
)
],
),
),
),
);
}
}