下拉菜单重置值(颤振) [英] Reset value on dropdown (Flutter)
问题描述
我有两个下拉菜单,分别是州和城市,基本上,当用户选择一个州时,它将自动设置州的城市值。当我选择州时,会出现城市的下拉列表,在我选择城市后,如果我想将州更改回去,则会出现错误
I have two dropdown which is states and cities, basically when user choose a state, it will automatically set the value of cities for the states. When i choose the state, the dropdown for cities appear, and after i choose the cities, if i want to change the state back, it will give error
另一个异常被抛出:'package:flutter / src / material / dropdown.dart':断言失败:行513位置15:'items == null || value == null || items.where((DropdownMenuItem item)=> item。 value == value).length == 1':不正确。
"Another exception was thrown: 'package:flutter/src/material/dropdown.dart': Failed assertion: line 513 pos 15: 'items == null || value == null || items.where((DropdownMenuItem item) => item.value == value).length == 1': is not true."
List state = [
"Kuala Lumpur",
"Selangor",
"Johor",
"Kedah",
"Kelantan",
"Melaka",
"Negeri Sembilan",
"Pahang",
"Penang",
"Perak",
"Perlis",
"Sabah",
"Sarawak",
"Terengganu"
];
List kl = [
"Ampang Hilir",
"Bandar Damai Perdana",
"Bandar Menjalara",
"Bandar Tasik Selatan",
"Bangsar",
"Bangsar South",];
List sel = [
"Ampang",
"Ara Damansara",
"Balakong",
"Bandar Bukit Raja",
"Bandar Kinrara",
"Bandar Puteri Puchong",
"Bandar Sunway",
"Bandar Utama",];
@override
void initState() {
super.initState();
_dropDownMenuStates = getDropDownMenuState();
}
List<DropdownMenuItem<String>> getDropDownMenuState() {
List<DropdownMenuItem<String>> state1 = new List();
for (String statelist in state) {
state1.add(
new DropdownMenuItem(value: statelist, child: new Text(statelist)));
}
return state1;
}
List<DropdownMenuItem<String>> getDropDownMenuKL() {
List<DropdownMenuItem<String>> kl1 = new List();
for (String kllist in kl) {
kl1.add(new DropdownMenuItem(value: kllist, child: new Text(kllist)));
}
return kl1;
}
List<DropdownMenuItem<String>> getDropDownMenuSEL() {
List<DropdownMenuItem<String>> sel1 = new List();
for (String sellist in sel) {
sel1.add(new DropdownMenuItem(value: sellist, child: new Text(sellist)));
}
return sel1;
}
Expanded(
child: PhysicalModel(
borderRadius:
new BorderRadius.circular(50.0),
color: Colors.white,
child: new Container(
padding: EdgeInsets.only(
left: 10.0, right: 10.0),
height: 40.0,
decoration: new BoxDecoration(
borderRadius:
new BorderRadius
.circular(50.0),
border: new Border.all(
width: 3.0,
color: Colors.grey[300],
)),
child: new FittedBox(
fit: BoxFit.contain,
child: DropdownButton(
hint: new Text(
allTranslations
.text('city')),
value: _currentCity,
items: _dropDownMenuCity,
onChanged:
changedDropDownCity,
),
))),
),
SizedBox(
width: 10.0,
),
Expanded(
child: PhysicalModel(
borderRadius:
new BorderRadius.circular(50.0),
color: Colors.white,
child: new Container(
padding: EdgeInsets.only(
left: 10.0, right: 10.0),
height: 40.0,
decoration: new BoxDecoration(
borderRadius:
new BorderRadius
.circular(50.0),
border: new Border.all(
width: 3.0,
color: Colors.grey[300],
)),
child: new FittedBox(
fit: BoxFit.contain,
child: DropdownButton(
hint: new Text(
allTranslations
.text('state')),
value: _currentState,
items: _dropDownMenuStates,
onChanged:
changedDropDownState,
),
))),
),
void changedDropDownState(String selectedState) {
setState(() {
_currentState = selectedState;
if (selectedState.toString() == "Kuala Lumpur") {
_dropDownMenuCity = getDropDownMenuKL();
} else if (selectedState.toString() == "Selangor") {
_dropDownMenuCity = getDropDownMenuSEL();}
});
}
void changedDropDownCity(String selectedCity) {
setState(() {
_currentCity = selectedCity;
});
}
推荐答案
您需要清除 _currentCity ,然后设置新的城市列表。
是因为 DropdownButton
在项中等待有效的
(_dropDownMenuCity)。值
(_currentCity)
You need clear _currentCity before set a new list of Cities.
Because the DropdownButton
wait a valid value
(_currentCity) in items
(_dropDownMenuCity).
void changedDropDownState(String selectedState) {
setState(() {
// <<<
_dropDownMenuCity = null;
_currentCity = null;
// <<<
_currentState = selectedState;
if (selectedState.toString() == "Kuala Lumpur") {
_dropDownMenuCity = getDropDownMenuKL();
} else if (selectedState.toString() == "Selangor") {
_dropDownMenuCity = getDropDownMenuSEL();
}
});
}
https://gist.github.com/dyegovieira/a2f78d241090a77939100e380987b8a1
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