我有这个脚本可以构建下拉列表
var date = DateTime.now();
print(date.toString()); // prints something like 2019-12-10 10:02:22.287949
print(DateFormat('EEEE').format(date)); // prints Tuesday
print(DateFormat('EEEE, d MMM, yyyy').format(date)); // prints Tuesday, 10 Dec, 2019
print(DateFormat('h:mm a').format(date)); // prints 10:02 AM
这是我的Future<List<AddressCst>> _address;
AddressCst selectedAddress;
Widget addressDropdown() {
return FutureBuilder<List<AddressCst>>(
future: _address,
initialData: [],
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.active ||
snapshot.connectionState == ConnectionState.waiting) {
return Center(
child: Container(
width: 20,
height: 20,
margin: EdgeInsets.all(10),
child: CircularProgressIndicator(
backgroundColor: Configuration.PrimaryColor,
),
));
} else if (snapshot.hasData) {
return DropdownButton<AddressCst>(
value: selectedAddress,
isExpanded: true,
items: snapshot.data.map((value) {
return DropdownMenuItem<AddressCst>(
value: value,
child: Text(
value.addressName,
style: TextStyle(fontSize: 17),
),
);
}).toList(),
hint: Text(
"Select Address",
style: TextStyle(fontSize: 17),
),
onChanged: (AddressCst choosen) {
setState(() {
selectedAddress = choosen;
});
},
);
} else if (snapshot.hasError) {
return Text("${snapshot.error}");
}
return Container(width: 0.0, height: 0.0);
});
}
课
AddressCst所以我想设置class AddressCst {
String deliveryAddressId;
String userId;
String addressName;
String addressProvinceId;
String addressCityId;
String addressRemark;
String addressLongitude;
String addressLatitude;
String cityName;
String provinceName;
AddressCst({
this.deliveryAddressId,
this.userId,
this.addressName,
this.addressProvinceId,
this.addressCityId,
this.addressRemark,
this.addressLongitude,
this.addressLatitude,
this.cityName,
this.provinceName,
});
factory AddressCst.fromJson(Map<String, dynamic> json) => AddressCst(
deliveryAddressId: json["deliveryAddressId"] == null
? null
: json["deliveryAddressId"],
userId: json["userId"] == null ? null : json["userId"],
addressName: json["addressName"] == null ? null : json["addressName"],
addressProvinceId: json["addressProvinceId"] == null
? null
: json["addressProvinceId"],
addressCityId:
json["addressCityId"] == null ? null : json["addressCityId"],
addressRemark:
json["addressRemark"] == null ? null : json["addressRemark"],
addressLongitude:
json["addressLongitude"] == null ? null : json["addressLongitude"],
addressLatitude:
json["addressLatitude"] == null ? null : json["addressLatitude"],
cityName: json["cityName"] == null ? null : json["cityName"],
provinceName:
json["provinceName"] == null ? null : json["provinceName"],
);
}
，所以我要从API获取数据，这就是我要做的
default value但是当我运行它时，出现此错误
以下断言被抛出 FutureBuilder>（脏，状态： _FutureBuilderState>＃d4ee6）：'package：flutter / src / material / dropdown.dart'：断言失败：行 620 pos 15：“项目== null || items.isEmpty ||值== null || items.where（（（DropdownMenuItem item）=> item.value == value）.length == 1'：不正确。
我该如何解决？我想念什么吗？