Set default value for dropdown button in flutter - flutter

Question

I have a dropdown button which works fine, but when I try to set a default value it will fail with the following error:
'package:flutter/src/material/dropdown.dart': Failed assertion: line 620 pos 15: 'items == null || items.isEmpty || value == null || items.where((DropdownMenuItem item) => item.value == value).length == 1': is not true.
This is my dropdown button:
Widget changeWorkspace() {
return StatefulBuilder(
builder: (BuildContext context, StateSetter setState) {
return Column(mainAxisSize: MainAxisSize.min, children: <Widget>[
Padding(
padding: EdgeInsets.all(8.0),
child: DropdownButton<AssignedWorkspace>(
isExpanded: true,
hint: Text("SELECT WORKSPACE"),
value: selectedWorkspace,
onChanged: (dropdownValueSelected) {
setState(() {
selectedWorkspace = dropdownValueSelected;
});
},
items: workspaces != null && workspaces.length > 0
? workspaces.map((AssignedWorkspace workspace) {
return new DropdownMenuItem<AssignedWorkspace>(
value: workspace,
child: new Text(workspace.name,
style: new TextStyle(color: Colors.black)),
);
}).toList()
: null),
),
]);
});
}
I've tried to set the value of selectedWorkspace onInit as follows but it fails.
selectedWorkspace = new AssignedWorkspace(
id: userSettings.currentWorkspaceId,
name: userSettings.currentWorkspaceName);
Is there a way of setting a default value in a dropdown button?

Answer 1

import 'package:flutter/material.dart';
import '../config/app_theme.dart';
class DropdownWidget extends StatefulWidget {
final String title;
final List<String> items;
final ValueChanged<String> itemCallBack;
final String currentItem;
final String hintText;
DropdownWidget({
this.title,
this.items,
this.itemCallBack,
this.currentItem,
this.hintText,
});
#override
State<StatefulWidget> createState() => _DropdownState(currentItem);
}
class _DropdownState extends State<DropdownWidget> {
List<DropdownMenuItem<String>> dropDownItems = [];
String currentItem;
AppTheme appTheme;
_DropdownState(this.currentItem);
#override
void initState() {
super.initState();
for (String item in widget.items) {
dropDownItems.add(DropdownMenuItem(
value: item,
child: Text(
item,
style: TextStyle(
fontSize: 16,
),
),
));
}
}
#override
void didUpdateWidget(DropdownWidget oldWidget) {
if (this.currentItem != widget.currentItem) {
setState(() {
this.currentItem = widget.currentItem;
});
}
super.didUpdateWidget(oldWidget);
}
#override
Widget build(BuildContext context) {
appTheme = AppTheme(Theme.of(context).brightness);
return Container(
margin: EdgeInsets.symmetric(vertical: 10),
child: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Container(
margin: EdgeInsets.only(left: 6),
child: Text(
widget.title,
style: appTheme.activityAddPageTextStyle,
),
),
Container(
padding: EdgeInsets.symmetric(vertical: 3, horizontal: 15),
margin: EdgeInsets.only(top: 10),
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(6),
color: Colors.white,
boxShadow: [
BoxShadow(
offset: Offset(0, 2),
blurRadius: 10,
color: Color(0x19000000),
),
],
),
child: DropdownButtonHideUnderline(
child: DropdownButton(
icon: appTheme.activityAddPageDownArrowSVG,
value: currentItem,
isExpanded: true,
items: dropDownItems,
onChanged: (selectedItem) => setState(() {
currentItem = selectedItem;
widget.itemCallBack(currentItem);
}),
hint: Container(
child: Text(widget.hintText, style: appTheme.hintStyle),
),
),
),
),
],
),
);
}
}
This is my dropDownWidget without optimization. It has currentItem. You could use it like:
DropdownWidget(
title: kStatus,
items: state.customerStepInfo.statusList,
currentItem: status,
hintText: kCommonPick,
itemCallBack: (String status) {
this.status = status;
},
)

Answer 2

You need implement "equals" in class AssignedWorkspace. I used equatable package.
Example class AssignedWorkspace
class AssignedWorkspace extends Equatable {
final String id;
final String name;
AssignedWorkspace(this.id, this.name);
#override
List<Object> get props => [id];
}

Answer 3

For me id of one of the element is null, once added id is made non-null issue got fixed.

Answer 4

I changed the value of the dropdown var to 1 initially
var _value = '1';
So when the dropdown button has to display its value it displays the one whose value I have set 1 as in the items list in DropDownButton
DropdownButton(
underline: Container(),
onChanged: (value) {
setState(() {
_value = value;
});
},
value: _value,
items: [
DropdownMenuItem(
value: "1",
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: <Widget>[
Icon(MaterialCommunityIcons.devices),
SizedBox(width: 10),
Text(
"Consumption",
style: TextStyle(
fontSize: 18.0, fontWeight: FontWeight.w600),
),
],
),
),
DropdownMenuItem(
value: "2",
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: <Widget>[
Icon(MaterialCommunityIcons.solar_panel),
SizedBox(width: 10),
Text(
"Generation",
style: TextStyle(
fontSize: 18.0, fontWeight: FontWeight.w600),
),
],
),
),
],
),

Answer 5

if you want to see only an initial value you can use hint text named parameter of drop down button and set a text widget. i dont know whether it is a good practice or not.