我正在尝试创建一个下拉按钮在颤振中。我得到了列表来自我的数据库然后我将列表传递给我的dropdownButton
一切正常数据按预期显示,但是当我从中选择一个元素时我收到此错误:
There should be exactly one item with [DropdownButton]'s value: Instance of 'Tag'.
Either zero or 2 or more [DropdownMenuItem]s were detected with the same value
'package:flutter/src/material/dropdown.dart':
Failed assertion: line 805 pos 15: 'items == null || items.isEmpty || value == null ||
items.where((DropdownMenuItem<T> item) {
return item.value == value;
}).length == 1'
我尝试设置DropdownButton 值为 null它有效,但后来我看不到所选元素.
这是我的代码:
FutureBuilder<List<Tag>>(
future: _tagDatabaseHelper.getTagList(),
builder: (BuildContext context, AsyncSnapshot<List<Tag>> snapshot) {
if (!snapshot.hasData) {
return Center(
child: CircularProgressIndicator(),
);
}
return ListView(
children: <Widget>[
SizedBox(
height: MediaQuery.of(context).size.height * 0.2,
),
Container(
margin: EdgeInsets.symmetric(
horizontal: MediaQuery.of(context).size.width * 0.07),
child: Theme(
data: ThemeData(canvasColor: Color(0xFF525A71)),
child: DropdownButton<Tag>(
value: _selectedTag,
isExpanded: true,
icon: Icon(
Icons.arrow_drop_down,
size: 24,
),
hint: Text(
"Select tags",
style: TextStyle(color: Color(0xFF9F9F9F)),
),
onChanged: (value) {
setState(() {
_selectedTag = value;
});
},
items: snapshot.data.map((Tag tag) {
return DropdownMenuItem<Tag>(
value: tag,
child: Text(
tag.tagTitle,
style: TextStyle(color: Colors.white),
),
);
}).toList(),
value: _selectedTag,
),
),
),
I used 未来建造者 to 从数据库获取我的列表.