颤振导航未定义的“上下文”
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【中文标题】颤振导航未定义的“上下文”【英文标题】：Flutter Navigation undefined "context" 【发布时间】：2020-02-25 12:58:11 【问题描述】：我是 flutter 和 dart 的新手，我正在尝试为应用程序构建一个注册。
我有一个开始屏幕 (StartPage)，其中包含“登录”、“登录 FB”、“使用电子邮件注册”选项。 当我点击“登录”时，我可以导航到 signup_email_screen。从那里我想导航到 signup_email_screen_two 但它抛出“未定义的名称上下文”。
class StartPage extends StatefulWidget
@override
_StartPageState createState() => _StartPageState();
class _StartPageState extends State<StartPage>
bool isAuth = false; //isAuth provides a bool if the user is already signed in
Widget buildAuthScreen()
return Text('Angemeldet');
Scaffold buildUnAuthScreen()
return Scaffold(
body: Container(
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/tenor.gif'),
fit: BoxFit.cover)),
alignment: Alignment.center,
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
crossAxisAlignment: CrossAxisAlignment.center,
children: [
SizedBox(height: SizeConfig.blockSizeVertical * 10),
Container(
width: SizeConfig.blockSizeHorizontal * 65,
height: SizeConfig.blockSizeVertical * 20,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/Insta_transparent.png'),
fit: BoxFit.scaleDown,
),
),
),
SizedBox(height: SizeConfig.blockSizeVertical * 0),
Text(
'Nie mehr Langeweile',
style: TextStyle(
fontFamily: "Signatra",
fontSize: SizeConfig.blockSizeHorizontal *8,
color: Colors.white,
),
),
SizedBox(height: SizeConfig.blockSizeVertical * 7),
GestureDetector(
onTap: () => _navigateToLogin(context),
child: Container(
width: SizeConfig.blockSizeHorizontal * 70,
height: SizeConfig.blockSizeVertical * 7,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/Log_In_Button.png'),
fit: BoxFit.scaleDown,
),
),
)),
SizedBox(height: SizeConfig.blockSizeVertical * 2),
GestureDetector(
onTap: () => print('facebook signin'),
child: Container(
width: SizeConfig.blockSizeHorizontal * 70,
height: SizeConfig.blockSizeVertical * 7,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/Log_In_Button_FB.png'),
fit: BoxFit.scaleDown,
),
),
),
),
SizedBox(height: SizeConfig.blockSizeVertical * 2),
GestureDetector(
onTap: () => _navigateToEmailRegister(context),
child: Container(
width: SizeConfig.blockSizeHorizontal * 60,
height: SizeConfig.blockSizeVertical *7,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage(
'assets/images/button-email-registration.png'),
fit: BoxFit.scaleDown,
),
),
),
),
],
),
),
);
void _navigateToLogin(BuildContext context)
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => LoginScreen(),
));
void _navigateToEmailRegister(BuildContext context)
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SignupEmailScreen(),
));
@override
Widget build(BuildContext context)
SizeConfig().init(context);
return isAuth ? buildAuthScreen() : buildUnAuthScreen();
class SignupEmailScreen extends StatelessWidget
Scaffold signupEmailScreen()
return Scaffold(
body: Stack(
children: [
Container(
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/StartPage_Background.jpg'),
fit: BoxFit.cover)),
alignment: Alignment.center,
),
//AppBar transparent and background full screen with Stack and Positioned
Positioned(
top: 0.0,
left: 0.0,
right: 0.0,
child: AppBar(
title: Text('Registrierung'),
backgroundColor: Colors.transparent, //transparent
elevation: 0.0, //Shadow gone
),
),
Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
SizedBox(height: SizeConfig.blockSizeVertical * 15),
//Insta image
Container(
width: SizeConfig.blockSizeHorizontal * 50,
height: SizeConfig.blockSizeVertical * 10,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/Insta_transparent.png'),
fit: BoxFit.scaleDown,
),
),
),
SizedBox(height: SizeConfig.blockSizeVertical * 7),
//Email text field
Padding(
padding: EdgeInsets.symmetric(
horizontal: SizeConfig.safeBlockHorizontal * 5),
child: TextField(
keyboardType: TextInputType.text,
style: TextStyle(color: Colors.white, fontSize: 20.0),
decoration: InputDecoration(
labelText: "Accountname",
labelStyle: TextStyle(
color: Colors.white,
),
hasFloatingPlaceholder: true,
enabledBorder: UnderlineInputBorder(
//Enables the border to change color
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
focusedBorder: UnderlineInputBorder(
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
),
),
),
//Password text field
Padding(
padding: EdgeInsets.symmetric(
horizontal: SizeConfig.safeBlockHorizontal * 5),
child: TextField(
keyboardType: TextInputType.emailAddress,
style: TextStyle(color: Colors.white, fontSize: 20.0),
decoration: InputDecoration(
labelText: "Email",
labelStyle: TextStyle(
color: Colors.white,
),
hasFloatingPlaceholder: true,
enabledBorder: UnderlineInputBorder(
//Enables the border to change color
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
focusedBorder: UnderlineInputBorder(
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
),
),
),
Padding(
padding: EdgeInsets.symmetric(
horizontal: SizeConfig.safeBlockHorizontal * 5),
child: TextField(
keyboardType: TextInputType.visiblePassword,
style: TextStyle(color: Colors.white, fontSize: 20.0),
decoration: InputDecoration(
labelText: "Passwort",
labelStyle: TextStyle(
color: Colors.white,
),
hasFloatingPlaceholder: true,
enabledBorder: UnderlineInputBorder(
//Enables the border to change color
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
focusedBorder: UnderlineInputBorder(
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
),
),
),
Padding(
padding: EdgeInsets.symmetric(
horizontal: SizeConfig.safeBlockHorizontal * 5),
child: TextField(
keyboardType: TextInputType.visiblePassword,
style: TextStyle(color: Colors.white, fontSize: 20.0),
decoration: InputDecoration(
labelText: "Passwort wiederholen",
labelStyle: TextStyle(
color: Colors.white,
),
hasFloatingPlaceholder: true,
enabledBorder: UnderlineInputBorder(
//Enables the border to change color
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
focusedBorder: UnderlineInputBorder(
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
),
),
),
SizedBox(height: SizeConfig.blockSizeVertical * 10),
//log in button
GestureDetector(
onTap: () => _navigateToSignupEmailScreenTwo(context),
child: Container(
width: SizeConfig.blockSizeHorizontal * 70,
height: SizeConfig.blockSizeVertical * 7,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/Log_In_Button.png'),
fit: BoxFit.scaleDown,
),
),
)),
],
),
],
),
);
//ACTIONS
void _navigateToSignupEmailScreenTwo(BuildContext context)
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SignupEmailScreenTwo(),
));
//BUILD
@override
Widget build(BuildContext context)
return signupEmailScreen();
class SignupEmailScreenTwo extends StatelessWidget
Scaffold signupEmailScreenTwo()
return Scaffold(
body: Stack(
children: [
Container(
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/StartPage_Background.jpg'),
fit: BoxFit.cover)),
alignment: Alignment.center,
),
//AppBar transparent and background full screen with Stack and Positioned
Positioned(
top: 0.0,
left: 0.0,
right: 0.0,
child: AppBar(
title: Text('Registrierung'),
backgroundColor: Colors.transparent, //transparent
elevation: 0.0, //Shadow gone
),
),
Column(
crossAxisAlignment: CrossAxisAlignment.center,
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
SizedBox(height: SizeConfig.blockSizeVertical * 15),
Container(
width: SizeConfig.blockSizeHorizontal * 50,
height: SizeConfig.blockSizeVertical * 10,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/Insta_transparent.png'),
fit: BoxFit.scaleDown,
),
),
),
SizedBox(height: SizeConfig.blockSizeVertical * 7),
//Email text field
Padding(
padding: EdgeInsets.symmetric(
horizontal: SizeConfig.safeBlockHorizontal * 5),
child: TextField(
keyboardType: TextInputType.text,
style: TextStyle(color: Colors.white, fontSize: 20.0),
decoration: InputDecoration(
labelText: "Dein Vorname",
labelStyle: TextStyle(
color: Colors.white,
),
hasFloatingPlaceholder: true,
enabledBorder: UnderlineInputBorder(
//Enables the border to change color
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
focusedBorder: UnderlineInputBorder(
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
),
),
),
//Password text field
Padding(
padding: EdgeInsets.symmetric(
horizontal: SizeConfig.safeBlockHorizontal * 5),
child: TextField(
keyboardType: TextInputType.datetime,
style: TextStyle(color: Colors.white, fontSize: 20.0),
decoration: InputDecoration(
labelText: "Dein Geburtsdatum",
labelStyle: TextStyle(
color: Colors.white,
),
hasFloatingPlaceholder: true,
enabledBorder: UnderlineInputBorder(
//Enables the border to change color
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
focusedBorder: UnderlineInputBorder(
borderSide:
BorderSide(color: Colors.white, width: 2.0)),
),
),
),
SizedBox(height: SizeConfig.blockSizeVertical * 10),
//log in button
GestureDetector(
onTap: () => print("Einlogggggeeeeeen"),
child: Container(
width: SizeConfig.blockSizeHorizontal * 70,
height: SizeConfig.blockSizeVertical * 7,
decoration: BoxDecoration(
image: DecorationImage(
image: AssetImage('assets/images/Log_In_Button.png'),
fit: BoxFit.scaleDown,
),
),
)),
],
),
],
),
);
@override
Widget build(BuildContext context)
return signupEmailScreenTwo();
为什么上下文未定义？ 感谢任何帮助！
【问题讨论】：
【参考方案1】：因为你的函数内部没有定义上下文:)
**编辑：**你无法访问StatelessWidget中的上下文对象
这些是你可以做的：
1- 使用StatefulWidget 而不是StatelessWidget，
2- 您可以将BuildContext context 作为parameter 传递到您的函数中。
3- 您可以在build 方法中编写所有小部件，而不是额外的函数。
【讨论】：
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