无法在 `null-safety` 版本的 flutter 中通过 `onGenerateRoute()` 传递 `arguments`
Cannot pass `arguments` through `onGenerateRoute()` in `null-safety` version of flutter
我想做什么?
像往常一样,我正在尝试将数据从一个屏幕发送到另一个屏幕 onGenerateRoute()
但我的屏幕不接受参数类型并显示错误 参数类型 'Object?' can' t被赋值给参数类型'Map<String, dynamic>'.
我还尝试在接收器屏幕上更改参数类型 Object?
,但现在我无法将数据从 Object
提取到 Map<String, dynamic>
。我认为两者是相同的数据类型,但空安全版本的处理方式不同。我认为这是一个错误。
我已经看到 flutter official documentation for navigate-with-arguments,当我在 交互示例 部分切换到 null-safety 时,它也显示错误。请查看此屏幕截图或自己尝试。
它在非空安全版本的 flutter 中正常工作
这是片段
路线生成器Class
class RouteGenerator {
static Route<dynamic> generateRoute(RouteSettings settings) {
// Getting arguments passed while calling Navigator.pushNamed
final args = settings.arguments;
switch (settings.name) {
case HomeScreen.routeName:
return MaterialPageRoute(
builder: (context) => HomeScreen(),
);
case LoginScreen.routeName:
return MaterialPageRoute(
builder: (context) => LoginScreen(),
);
case VerifyFirebaseOtpScreen.routeName:
return MaterialPageRoute(
builder: (context) => VerifyFirebaseOtpScreen(data: args), // Here is the error: The argument type 'Object?' can't be assigned to the parameter type 'Map<String, dynamic>'.
);
case AboutScreen.routeName:
return MaterialPageRoute(
builder: (context) => AboutScreen(),
);
default:
return MaterialPageRoute(
builder: (context) => Scaffold(
body: SafeArea(
child: Center(
child: Text('No route defined for ${settings.name}'),
),
),
),
);
}
}
}
验证FirebaseOtpScreen
class VerifyFirebaseOtpScreen extends StatelessWidget {
static const String routeName = '/verify_firebase_otp_screen';
final Map<String, dynamic> data;
const VerifyFirebaseOtpScreen({
Key? key,
required this.data,
}) : super(key: key);
@override
Widget build(BuildContext context) {
return GestureDetector(
onTap: () {
FocusScope.of(context).unfocus();
},
child: Scaffold(
body: Center(
child: SingleChildScrollView(
padding: const EdgeInsets.all(8.0),
child: Container(
width: double.infinity,
child: VerifyFirebaseOtpScreenDataSection(
mobile: '${data['mobile']}',
),
),
),
),
),
);
}
}
日志
abhishekkumar@Abhisheks-MacBook-Air ~ % flutter doctor -v
[✓] Flutter (Channel beta, 2.1.0-12.2.pre, on macOS 11.2.3 20D91 darwin-x64, locale en-IN)
• Flutter version 2.1.0-12.2.pre at /Users/abhishekkumar/flutter
• Framework revision 5bedb7b1d5 (13 days ago), 2021-03-17 17:06:30 -0700
• Engine revision 711ab3fda0
• Dart version 2.13.0 (build 2.13.0-116.0.dev)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
• Android SDK at /Users/abhishekkumar/Library/Android/sdk
• Platform android-30, build-tools 30.0.2
• ANDROID_HOME = /Users/abhishekkumar/Library/Android/sdk
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
• All Android licenses accepted.
[✓] Xcode - develop for iOS and macOS
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 12.4, Build version 12D4e
• CocoaPods version 1.10.1
[✓] Chrome - develop for the web
• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
[✓] Android Studio (version 4.1)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin can be installed from:
https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
[✓] VS Code (version 1.51.1)
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension version 3.17.0
[✓] Connected device (3 available)
• iPhone SE (1st generation) (mobile) • 035FA189-09FF-46B5-96AC-C34E8D068C21 • ios • com.apple.CoreSimulator.SimRuntime.iOS-14-4 (simulator)
• macOS (desktop) • macos • darwin-x64 • macOS 11.2.3 20D91 darwin-x64
• Chrome (web) • chrome • web-javascript • Google Chrome 89.0.4389.90
• No issues found!
简答
使用类型转换运算符as
所以上面问题的答案就像 final args = settings.arguments as Map<String, dynamic>;
回答说明
我也将这个问题提交为 an issue on GitHub and thanks to goderbauer (A Flutter Team Member) who identify correctly this issue and closed it by giving an appropriate solution。
goderbauer 说
In your example settings.arguments
is typed as Object?
and you're passing it to VerifyFirebaseOtpScreen.data
which is typed as Map<String, dynamic>
. Prior to null-safety this was legal and is called an implicit downcast. But with null safety Dart has removed implicit downcast altogether (you can read more about that here https://dart.dev/null-safety/understanding-null-safety, just search for "implicit downcast" on the page). So now, if you're sure that settings.arguments
is in deed of type Map<String, dynamic>
you need to do an explicit cast, something like: settings.arguments as Map<String, dynamic>
.
他还说
(The example on the page will have to be updated as well once we migrate them to null safety)
dart.dev 解释和例子
参考文档页面 Understanding null-safety & using-nullable-types 解释也涵盖了这一点。
他们下面的例子已经足够解释了
// Without null safety:
requireStringNotObject(String definitelyString) {
print(definitelyString.length);
}
main() {
Object maybeString = 'it is';
requireStringNotObject(maybeString);
}
// Using null safety:
requireStringNotObject(String definitelyString) {
print(definitelyString.length);
}
main() {
Object maybeString = 'it is';
requireStringNotObject(maybeString as String);
}
我想做什么?
像往常一样,我正在尝试将数据从一个屏幕发送到另一个屏幕 onGenerateRoute()
但我的屏幕不接受参数类型并显示错误 参数类型 'Object?' can' t被赋值给参数类型'Map<String, dynamic>'.
我还尝试在接收器屏幕上更改参数类型 Object?
,但现在我无法将数据从 Object
提取到 Map<String, dynamic>
。我认为两者是相同的数据类型,但空安全版本的处理方式不同。我认为这是一个错误。
我已经看到 flutter official documentation for navigate-with-arguments,当我在 交互示例 部分切换到 null-safety 时,它也显示错误。请查看此屏幕截图或自己尝试。
它在非空安全版本的 flutter 中正常工作
这是片段
路线生成器Class
class RouteGenerator {
static Route<dynamic> generateRoute(RouteSettings settings) {
// Getting arguments passed while calling Navigator.pushNamed
final args = settings.arguments;
switch (settings.name) {
case HomeScreen.routeName:
return MaterialPageRoute(
builder: (context) => HomeScreen(),
);
case LoginScreen.routeName:
return MaterialPageRoute(
builder: (context) => LoginScreen(),
);
case VerifyFirebaseOtpScreen.routeName:
return MaterialPageRoute(
builder: (context) => VerifyFirebaseOtpScreen(data: args), // Here is the error: The argument type 'Object?' can't be assigned to the parameter type 'Map<String, dynamic>'.
);
case AboutScreen.routeName:
return MaterialPageRoute(
builder: (context) => AboutScreen(),
);
default:
return MaterialPageRoute(
builder: (context) => Scaffold(
body: SafeArea(
child: Center(
child: Text('No route defined for ${settings.name}'),
),
),
),
);
}
}
}
验证FirebaseOtpScreen
class VerifyFirebaseOtpScreen extends StatelessWidget {
static const String routeName = '/verify_firebase_otp_screen';
final Map<String, dynamic> data;
const VerifyFirebaseOtpScreen({
Key? key,
required this.data,
}) : super(key: key);
@override
Widget build(BuildContext context) {
return GestureDetector(
onTap: () {
FocusScope.of(context).unfocus();
},
child: Scaffold(
body: Center(
child: SingleChildScrollView(
padding: const EdgeInsets.all(8.0),
child: Container(
width: double.infinity,
child: VerifyFirebaseOtpScreenDataSection(
mobile: '${data['mobile']}',
),
),
),
),
),
);
}
}
日志
abhishekkumar@Abhisheks-MacBook-Air ~ % flutter doctor -v
[✓] Flutter (Channel beta, 2.1.0-12.2.pre, on macOS 11.2.3 20D91 darwin-x64, locale en-IN)
• Flutter version 2.1.0-12.2.pre at /Users/abhishekkumar/flutter
• Framework revision 5bedb7b1d5 (13 days ago), 2021-03-17 17:06:30 -0700
• Engine revision 711ab3fda0
• Dart version 2.13.0 (build 2.13.0-116.0.dev)
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
• Android SDK at /Users/abhishekkumar/Library/Android/sdk
• Platform android-30, build-tools 30.0.2
• ANDROID_HOME = /Users/abhishekkumar/Library/Android/sdk
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
• All Android licenses accepted.
[✓] Xcode - develop for iOS and macOS
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 12.4, Build version 12D4e
• CocoaPods version 1.10.1
[✓] Chrome - develop for the web
• Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
[✓] Android Studio (version 4.1)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin can be installed from:
https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6915495)
[✓] VS Code (version 1.51.1)
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension version 3.17.0
[✓] Connected device (3 available)
• iPhone SE (1st generation) (mobile) • 035FA189-09FF-46B5-96AC-C34E8D068C21 • ios • com.apple.CoreSimulator.SimRuntime.iOS-14-4 (simulator)
• macOS (desktop) • macos • darwin-x64 • macOS 11.2.3 20D91 darwin-x64
• Chrome (web) • chrome • web-javascript • Google Chrome 89.0.4389.90
• No issues found!
简答
使用类型转换运算符as
所以上面问题的答案就像 final args = settings.arguments as Map<String, dynamic>;
回答说明
我也将这个问题提交为 an issue on GitHub and thanks to goderbauer (A Flutter Team Member) who identify correctly this issue and closed it by giving an appropriate solution。
goderbauer 说
In your example
settings.arguments
is typed asObject?
and you're passing it toVerifyFirebaseOtpScreen.data
which is typed asMap<String, dynamic>
. Prior to null-safety this was legal and is called an implicit downcast. But with null safety Dart has removed implicit downcast altogether (you can read more about that here https://dart.dev/null-safety/understanding-null-safety, just search for "implicit downcast" on the page). So now, if you're sure thatsettings.arguments
is in deed of typeMap<String, dynamic>
you need to do an explicit cast, something like:settings.arguments as Map<String, dynamic>
.
他还说
(The example on the page will have to be updated as well once we migrate them to null safety)
dart.dev 解释和例子
参考文档页面 Understanding null-safety & using-nullable-types 解释也涵盖了这一点。
他们下面的例子已经足够解释了
// Without null safety:
requireStringNotObject(String definitelyString) {
print(definitelyString.length);
}
main() {
Object maybeString = 'it is';
requireStringNotObject(maybeString);
}
// Using null safety:
requireStringNotObject(String definitelyString) {
print(definitelyString.length);
}
main() {
Object maybeString = 'it is';
requireStringNotObject(maybeString as String);
}