颤振组合框
Flutter combo box
我正在尝试创建一个下拉菜单/组合框小部件，但我很难理解。下面是我试过的代码。基本上是创建一个我从各处收集但无法将其相应地放入我自己的代码中的列表。
import 'package:flutter/material.dart';
class Signup extends StatefulWidget{
Signup({Key key}) : super (key:key);
final String title;
@override
SignupPage createState() => new SignupPage();
}
class SignupPage extends State<Signup> {
@override
Widget build(BuildContext context) {
List _countrycodes = ["+65","+91"];
List<DropdownMenuItem<String>> _dropDownMenuItems;
String _selectedCountryCode;
List<String> _colors = <String>['', 'red', 'green', 'blue', 'orange'];
String _color = '';
List<DropdownMenuItem<String>> getDropDownMenuItems() {
List<DropdownMenuItem<String>> items = new List();
for (String code in _countrycodes) {
items.add(new DropdownMenuItem(
value: code,
child: new Text(code)
));
}
return items;
}
/**return new Material(
color: Colors.blueAccent,
child: new Scaffold(
body: new Stack(
children: <Widget>[
new Container(
decoration: new BoxDecoration(
image: new DecorationImage(image: new AssetImage("assets/images/download.jpg"), fit: BoxFit.cover,),
),
),
new Center(
child: new Text("Hello LandingPage"),
)
],
)
));**/
final name = TextFormField(
keyboardType: TextInputType.text,
autofocus: false,
initialValue: 'Techie Quickie',
decoration: InputDecoration(
hintText: 'Name',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final email = TextFormField(
keyboardType: TextInputType.emailAddress,
autofocus: false,
initialValue: 'tq@gmail.com',
decoration: InputDecoration(
hintText: 'Email',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final password = TextFormField(
keyboardType: TextInputType.text,
obscureText: true,
autofocus: false,
initialValue: 'password',
decoration: InputDecoration(
hintText: 'Password',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final passwordConfirmation = TextFormField(
keyboardType: TextInputType.text,
obscureText: true,
autofocus: false,
initialValue: 'password',
decoration: InputDecoration(
hintText: 'Password',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final loginButton = Padding(
padding: EdgeInsets.symmetric(vertical: 16.0),
child: Material(
borderRadius: BorderRadius.circular(30.0),
shadowColor: Colors.lightBlueAccent.shade100,
elevation: 5.0,
child: MaterialButton(
minWidth: 200.0,
height: 42.0,
onPressed: (){
print("Signup button clicked");
},
color: Colors.lightBlueAccent,
child:
Text('Sign Up',
style: TextStyle(color: Colors.white, fontSize: 20.0),
),
),
)
);
final countryCode = DropdownButton(
value: _selectedCountryCode,
items: _dropDownMenuItems,
onChanged: null
);
final inputDecoratoring =InputDecorator(
decoration: const InputDecoration(
icon: const Icon(Icons.color_lens),
labelText: 'Color',
),
isEmpty: _color == '',
child: new DropdownButtonHideUnderline(
child: new DropdownButton<String>(
value: _color,
isDense: true,
onChanged: (String newValue) {
setState(() {
_color = newValue;
});
},
items: _colors.map((String value) {
return new DropdownMenuItem<String>(
value: value,
child: new Text(value),
);
}).toList(),
),
),
);
return Scaffold(
backgroundColor: Colors.white,
body: Center (
child: ListView(
padding: EdgeInsets.only(left: 24.0, right: 24.0),
shrinkWrap: true,
children: <Widget>[
name,
SizedBox(height: 18.0),
email,
SizedBox(height: 18.0),
password,
SizedBox(height: 18.0),
passwordConfirmation,
SizedBox(height: 18.0),
// countryCode,
// SizedBox(height: 18.0),
loginButton,
SizedBox(height: 38.0),
],
)
)
);
}
}
这是我的main.dartclass
import 'package:flutter/material.dart';
import 'package:elegal_dart/screens/landing_page.dart';
import 'package:elegal_dart/screens/home.dart';
import 'package:elegal_dart/screens/devices.dart';
import 'package:elegal_dart/screens/signup.dart';
import 'package:elegal_dart/screens/signin.dart';
/*
void main()
{
Devices( new MaterialApp(
home: new Devices(),
));
}*/
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget
{
@override
Widget build(BuildContext context)
{
return new MaterialApp(
title: 'Navigation',
routes: <String, WidgetBuilder>
{
'/Home' : (BuildContext context) => new Home(),
'/LandingPage' : (BuildContext context) => new LandingPage(),
'/Devices' : (BuildContext context) => new Devices(),
'/Signup' : (BuildContext context) => new Signup(),
'/Signin' : (BuildContext context) => new Signin(),
},
//home: new Signin(onSubmit: null),
home: new Signup(),
);
}
}
更新代码：
import 'package:flutter/material.dart';
class Signup extends StatefulWidget{
Signup({Key key}) : super (key:key);
final String title;
@override
SignupPage createState() => new SignupPage();
}
class SignupPage extends State<Signup> {
@override
Widget build(BuildContext context) {
List _countrycodes = ["+65","+91"];
List<DropdownMenuItem<String>> _dropDownMenuItems;
String _selectedCountryCode;
List<String> _ccodes = <String>['', '+65', '+91', '+60', 'orange'];
String _ccode = '';
List<DropdownMenuItem<String>> getDropDownMenuItems() {
List<DropdownMenuItem<String>> items = new List();
for (String code in _countrycodes) {
items.add(new DropdownMenuItem(
value: code,
child: new Text(code)
));
}
return items;
}
final name = TextFormField(
keyboardType: TextInputType.text,
autofocus: false,
initialValue: 'Techie Quickie',
decoration: InputDecoration(
hintText: 'Name',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final email = TextFormField(
keyboardType: TextInputType.emailAddress,
autofocus: false,
initialValue: 'tq@gmail.com',
decoration: InputDecoration(
hintText: 'Email',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final password = TextFormField(
keyboardType: TextInputType.text,
obscureText: true,
autofocus: false,
initialValue: 'password',
decoration: InputDecoration(
hintText: 'Password',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final passwordConfirmation = TextFormField(
keyboardType: TextInputType.text,
obscureText: true,
autofocus: false,
initialValue: 'password',
decoration: InputDecoration(
hintText: 'Password',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final loginButton = Padding(
padding: EdgeInsets.symmetric(vertical: 16.0),
child: Material(
borderRadius: BorderRadius.circular(30.0),
shadowColor: Colors.lightBlueAccent.shade100,
elevation: 5.0,
child: MaterialButton(
minWidth: 200.0,
height: 42.0,
onPressed: (){
print("Signup button clicked");
},
color: Colors.lightBlueAccent,
child:
Text('Sign Up',
style: TextStyle(color: Colors.white, fontSize: 20.0),
),
),
)
);
final countryCode = DropdownButtonHideUnderline (
child: DropdownButton<String>(
value: _ccode,
isDense: true,
items: _ccodes.map((String value) {
return new DropdownMenuItem<String>(
value: value,
child: new Text(value),
);
}).toList(),
onChanged: (String newValue) {
setState(() {
_ccode = newValue;
});
}
)
);
return Scaffold(
backgroundColor: Colors.white,
body: Center (
child: ListView(
padding: EdgeInsets.only(left: 24.0, right: 24.0),
shrinkWrap: true,
children: <Widget>[
name,
SizedBox(height: 18.0),
email,
SizedBox(height: 18.0),
password,
SizedBox(height: 18.0),
passwordConfirmation,
SizedBox(height: 18.0),
countryCode,
SizedBox(height: 18.0),
loginButton,
SizedBox(height: 38.0),
],
)
)
);
}
}
我在 AVD 中遇到的错误
断言告诉您 items 不能为空。它指的是这个：items: _dropDownMenuItems,。你永远不会分配 _dropDownMenuItems.
这是 Dart-y 模式的一个很好的用途。将其替换为：
final countryCode = DropdownButton(
value: _selectedCountryCode,
items: _countrycodes
.map((code) =>
new DropdownMenuItem(value: code, child: new Text(code)))
.toList(),
onChanged: null,
);
并且您不再需要该字段或 getDropDownMenuItems 函数。如果您不熟悉此语法，请将其阅读为 "map each code in countryCodes to a DropdownMenuItem and form them back into a List"
另外，你的变量范围是错误的。将它们移出构建函数并进入状态，如下所示：
class SignupPage extends State<Signup> {
List<String> _countrycodes = ["+65", "+91"];
List<String> _colors = ['', 'red', 'green', 'blue', 'orange'];
String _selectedCountryCode;
String _color = '';
我的回答也将解决在同一页面中使用多个 DropdownButton 而不会出现 DropdownMenuItem 中超过 1 个项目的错误的问题。
首先定义您将以这种方式使用的列表：
static const List<String> _razas = const
["Schnauzer", "Ovejero Alemán", "Husky", "Brasov",
"Constanta","Mestizo"];
////////barrios
static const List<String> _barrios = const
"Belgrano", "Caballito", "Colegiales", "Lugano", "Palermo","Pilar",
"Montserrat", "Vicente López" ];
static const List<String> _tamanio = const
["Chico", "Mediano", "Grande" ];
String tamanioValue = _tamanio[0];
String barriosValue = _barrios[0];
String razasValue = _razas[0];
然后在您的脚手架中使用这个容器
Container(
margin: EdgeInsets.only(top:20.0, bottom: 20.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.start,
children:<Widget> [
Text("RAZA "),
new DropdownButton(value:razasValue,
onChanged: (string) => setState(() => razasValue =
string),
items: _razas.map((string) {
return new DropdownMenuItem(
child: new Text(string),
value: string,
);
}).toList(),
),
]
)
),
Container(
margin: EdgeInsets.only(top:20.0, bottom: 20.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.start,
children:<Widget> [
Text("BARRIO "),
new DropdownButton(value:barriosValue,
onChanged: (string) => setState(() =>
barriosValue = string),
items: _barrios.map((string) {
return new DropdownMenuItem(
child: new Text(string),
value: string,
);
}).toList(),
),
]
)
),
然后只需替换您的数据库或您存储数据的任何文件的值
raza: razasValue,
barrio: barriosValue,
我正在尝试创建一个下拉菜单/组合框小部件，但我很难理解。下面是我试过的代码。基本上是创建一个我从各处收集但无法将其相应地放入我自己的代码中的列表。
import 'package:flutter/material.dart';
class Signup extends StatefulWidget{
Signup({Key key}) : super (key:key);
final String title;
@override
SignupPage createState() => new SignupPage();
}
class SignupPage extends State<Signup> {
@override
Widget build(BuildContext context) {
List _countrycodes = ["+65","+91"];
List<DropdownMenuItem<String>> _dropDownMenuItems;
String _selectedCountryCode;
List<String> _colors = <String>['', 'red', 'green', 'blue', 'orange'];
String _color = '';
List<DropdownMenuItem<String>> getDropDownMenuItems() {
List<DropdownMenuItem<String>> items = new List();
for (String code in _countrycodes) {
items.add(new DropdownMenuItem(
value: code,
child: new Text(code)
));
}
return items;
}
/**return new Material(
color: Colors.blueAccent,
child: new Scaffold(
body: new Stack(
children: <Widget>[
new Container(
decoration: new BoxDecoration(
image: new DecorationImage(image: new AssetImage("assets/images/download.jpg"), fit: BoxFit.cover,),
),
),
new Center(
child: new Text("Hello LandingPage"),
)
],
)
));**/
final name = TextFormField(
keyboardType: TextInputType.text,
autofocus: false,
initialValue: 'Techie Quickie',
decoration: InputDecoration(
hintText: 'Name',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final email = TextFormField(
keyboardType: TextInputType.emailAddress,
autofocus: false,
initialValue: 'tq@gmail.com',
decoration: InputDecoration(
hintText: 'Email',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final password = TextFormField(
keyboardType: TextInputType.text,
obscureText: true,
autofocus: false,
initialValue: 'password',
decoration: InputDecoration(
hintText: 'Password',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final passwordConfirmation = TextFormField(
keyboardType: TextInputType.text,
obscureText: true,
autofocus: false,
initialValue: 'password',
decoration: InputDecoration(
hintText: 'Password',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final loginButton = Padding(
padding: EdgeInsets.symmetric(vertical: 16.0),
child: Material(
borderRadius: BorderRadius.circular(30.0),
shadowColor: Colors.lightBlueAccent.shade100,
elevation: 5.0,
child: MaterialButton(
minWidth: 200.0,
height: 42.0,
onPressed: (){
print("Signup button clicked");
},
color: Colors.lightBlueAccent,
child:
Text('Sign Up',
style: TextStyle(color: Colors.white, fontSize: 20.0),
),
),
)
);
final countryCode = DropdownButton(
value: _selectedCountryCode,
items: _dropDownMenuItems,
onChanged: null
);
final inputDecoratoring =InputDecorator(
decoration: const InputDecoration(
icon: const Icon(Icons.color_lens),
labelText: 'Color',
),
isEmpty: _color == '',
child: new DropdownButtonHideUnderline(
child: new DropdownButton<String>(
value: _color,
isDense: true,
onChanged: (String newValue) {
setState(() {
_color = newValue;
});
},
items: _colors.map((String value) {
return new DropdownMenuItem<String>(
value: value,
child: new Text(value),
);
}).toList(),
),
),
);
return Scaffold(
backgroundColor: Colors.white,
body: Center (
child: ListView(
padding: EdgeInsets.only(left: 24.0, right: 24.0),
shrinkWrap: true,
children: <Widget>[
name,
SizedBox(height: 18.0),
email,
SizedBox(height: 18.0),
password,
SizedBox(height: 18.0),
passwordConfirmation,
SizedBox(height: 18.0),
// countryCode,
// SizedBox(height: 18.0),
loginButton,
SizedBox(height: 38.0),
],
)
)
);
}
}
这是我的main.dartclass
import 'package:flutter/material.dart';
import 'package:elegal_dart/screens/landing_page.dart';
import 'package:elegal_dart/screens/home.dart';
import 'package:elegal_dart/screens/devices.dart';
import 'package:elegal_dart/screens/signup.dart';
import 'package:elegal_dart/screens/signin.dart';
/*
void main()
{
Devices( new MaterialApp(
home: new Devices(),
));
}*/
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget
{
@override
Widget build(BuildContext context)
{
return new MaterialApp(
title: 'Navigation',
routes: <String, WidgetBuilder>
{
'/Home' : (BuildContext context) => new Home(),
'/LandingPage' : (BuildContext context) => new LandingPage(),
'/Devices' : (BuildContext context) => new Devices(),
'/Signup' : (BuildContext context) => new Signup(),
'/Signin' : (BuildContext context) => new Signin(),
},
//home: new Signin(onSubmit: null),
home: new Signup(),
);
}
}
更新代码：
import 'package:flutter/material.dart';
class Signup extends StatefulWidget{
Signup({Key key}) : super (key:key);
final String title;
@override
SignupPage createState() => new SignupPage();
}
class SignupPage extends State<Signup> {
@override
Widget build(BuildContext context) {
List _countrycodes = ["+65","+91"];
List<DropdownMenuItem<String>> _dropDownMenuItems;
String _selectedCountryCode;
List<String> _ccodes = <String>['', '+65', '+91', '+60', 'orange'];
String _ccode = '';
List<DropdownMenuItem<String>> getDropDownMenuItems() {
List<DropdownMenuItem<String>> items = new List();
for (String code in _countrycodes) {
items.add(new DropdownMenuItem(
value: code,
child: new Text(code)
));
}
return items;
}
final name = TextFormField(
keyboardType: TextInputType.text,
autofocus: false,
initialValue: 'Techie Quickie',
decoration: InputDecoration(
hintText: 'Name',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final email = TextFormField(
keyboardType: TextInputType.emailAddress,
autofocus: false,
initialValue: 'tq@gmail.com',
decoration: InputDecoration(
hintText: 'Email',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final password = TextFormField(
keyboardType: TextInputType.text,
obscureText: true,
autofocus: false,
initialValue: 'password',
decoration: InputDecoration(
hintText: 'Password',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final passwordConfirmation = TextFormField(
keyboardType: TextInputType.text,
obscureText: true,
autofocus: false,
initialValue: 'password',
decoration: InputDecoration(
hintText: 'Password',
contentPadding: EdgeInsets.fromLTRB(20.0, 10.0, 20.0, 10.0),
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(32.0)
),
),
);
final loginButton = Padding(
padding: EdgeInsets.symmetric(vertical: 16.0),
child: Material(
borderRadius: BorderRadius.circular(30.0),
shadowColor: Colors.lightBlueAccent.shade100,
elevation: 5.0,
child: MaterialButton(
minWidth: 200.0,
height: 42.0,
onPressed: (){
print("Signup button clicked");
},
color: Colors.lightBlueAccent,
child:
Text('Sign Up',
style: TextStyle(color: Colors.white, fontSize: 20.0),
),
),
)
);
final countryCode = DropdownButtonHideUnderline (
child: DropdownButton<String>(
value: _ccode,
isDense: true,
items: _ccodes.map((String value) {
return new DropdownMenuItem<String>(
value: value,
child: new Text(value),
);
}).toList(),
onChanged: (String newValue) {
setState(() {
_ccode = newValue;
});
}
)
);
return Scaffold(
backgroundColor: Colors.white,
body: Center (
child: ListView(
padding: EdgeInsets.only(left: 24.0, right: 24.0),
shrinkWrap: true,
children: <Widget>[
name,
SizedBox(height: 18.0),
email,
SizedBox(height: 18.0),
password,
SizedBox(height: 18.0),
passwordConfirmation,
SizedBox(height: 18.0),
countryCode,
SizedBox(height: 18.0),
loginButton,
SizedBox(height: 38.0),
],
)
)
);
}
}
我在 AVD 中遇到的错误
断言告诉您 items 不能为空。它指的是这个：items: _dropDownMenuItems,。你永远不会分配 _dropDownMenuItems.
这是 Dart-y 模式的一个很好的用途。将其替换为：
final countryCode = DropdownButton(
value: _selectedCountryCode,
items: _countrycodes
.map((code) =>
new DropdownMenuItem(value: code, child: new Text(code)))
.toList(),
onChanged: null,
);
并且您不再需要该字段或 getDropDownMenuItems 函数。如果您不熟悉此语法，请将其阅读为 "map each code in countryCodes to a DropdownMenuItem and form them back into a List"
另外，你的变量范围是错误的。将它们移出构建函数并进入状态，如下所示：
class SignupPage extends State<Signup> {
List<String> _countrycodes = ["+65", "+91"];
List<String> _colors = ['', 'red', 'green', 'blue', 'orange'];
String _selectedCountryCode;
String _color = '';
我的回答也将解决在同一页面中使用多个 DropdownButton 而不会出现 DropdownMenuItem 中超过 1 个项目的错误的问题。 首先定义您将以这种方式使用的列表：
static const List<String> _razas = const
["Schnauzer", "Ovejero Alemán", "Husky", "Brasov",
"Constanta","Mestizo"];
////////barrios
static const List<String> _barrios = const
"Belgrano", "Caballito", "Colegiales", "Lugano", "Palermo","Pilar",
"Montserrat", "Vicente López" ];
static const List<String> _tamanio = const
["Chico", "Mediano", "Grande" ];
String tamanioValue = _tamanio[0];
String barriosValue = _barrios[0];
String razasValue = _razas[0];
然后在您的脚手架中使用这个容器
Container(
margin: EdgeInsets.only(top:20.0, bottom: 20.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.start,
children:<Widget> [
Text("RAZA "),
new DropdownButton(value:razasValue,
onChanged: (string) => setState(() => razasValue =
string),
items: _razas.map((string) {
return new DropdownMenuItem(
child: new Text(string),
value: string,
);
}).toList(),
),
]
)
),
Container(
margin: EdgeInsets.only(top:20.0, bottom: 20.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.start,
children:<Widget> [
Text("BARRIO "),
new DropdownButton(value:barriosValue,
onChanged: (string) => setState(() =>
barriosValue = string),
items: _barrios.map((string) {
return new DropdownMenuItem(
child: new Text(string),
value: string,
);
}).toList(),
),
]
)
),
然后只需替换您的数据库或您存储数据的任何文件的值
raza: razasValue,
barrio: barriosValue,