我有两个下拉菜单,第二个取决于第一个。
当我在选择第二个下拉值后更改第一个下拉值时,它会引发如下错误。
那么如果我更改了第一个下拉值,如何重置第二个下拉列表?
下拉按钮如下。
DropdownButtonFormField<Standard>(
validator: (value) {
if (value == null) {
return "Select Standard";
}
},
isExpanded: true,
hint: Text('Select Standard'),
value: selectedStandard,
items: _standards.map((Standard standard) {
return DropdownMenuItem<Standard>(
value: standard,
child: Text(standard.standardName),
);
}).toList(),
onChanged: (val) {
setState(() {
selectedStandard = val;
standardId = val?.standardId;
onMediumChange(val);
});
}),
SizedBox(height: 20),
DropdownButtonFormField<Medium>(
validator: (value) {
if (value == null) {
return "Select Medium";
}
},
isExpanded: true,
hint: Text('Select Medium'),
value: selectedMedium,
items: _mediums.map((Medium medium) {
return DropdownMenuItem<Medium>(
value: medium,
child: Text(medium.mediumName),
);
}).toList(),
onChanged: (val) {
setState(() {
selectedMedium = val;
mediumId = val?.mediumId;
});
}),
并获取值代码如下。我使用的变量。
var _standards = <Standard>[];
var _mediums = <Medium>[];
Standard? selectedStandard;
Medium? selectedMedium;
@override
void initState() {
super.initState();
ApiManager().getStandards().then((standards) {
setState(() {
_standards = standards;
});
});
}
void onMediumChange(standard) {
setState(() {
selectedStandard = standard;
_mediums = [];
});
String mediumUrl =
"$baseUrl/medium/get_by_course_id?standard_id=${selectedStandard?.standardId}";
ApiManager().getMediums(mediumUrl).then((List<Medium> value) => {
setState(() {
_mediums = value;
})
});
}
据我了解有问题 selectedMedium
尝试更改使其选中null
中onMediumChange
void onMediumChange(standard) {
setState(() {
selectedMedium = null;
selectedStandard = standard;
_mediums = [];
});
String mediumUrl =
"$baseUrl/medium/get_by_course_id?standard_id=${selectedStandard?.standardId}";
ApiManager().getMediums(mediumUrl).then((List<Medium> value) => {
setState(() {
_mediums = value;
})
});
}
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