如何解决无法在 flutter RouteGenerator 类VerifyFirebaseOtpScreen戈德鲍尔说
我想做什么?
像往常一样,我试图将数据从一个屏幕发送到另一个 onGenerateRoute()
,但我的屏幕不接受参数类型并显示错误 参数类型“对象?”无法分配给参数类型“Map
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>
。我认为两者都是相同的数据类型,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 并且当我在 Interactive example 部分切换到 null-safety 时,它也显示错误。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
RouteGenerator 类
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 ${settings.name}'),),);
}
}
}
VerifyFirebaseOtpScreen
class VerifyFirebaseOtpScreen extends StatelessWidget {
static const String routeName = '/verify_firebase_otp_screen';
final Map<String,dynamic> data;
const VerifyFirebaseOtpScreen({
Key? key,required this.data,}) : super(key: key);
@override
Widget build(BuildContext context) {
return GestureDetector(
onTap: () {
FocusScope.of(context).unfocus();
},child: Scaffold(
body: Center(
child: SingleChildScrollView(
padding: const EdgeInsets.all(8.0),child: Container(
width: double.infinity,child: VerifyFirebaseOtpScreenDataSection(
mobile: '${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!
解决方法
简单回答
使用类型转换运算符 as
所以上述问题的答案将类似于 final args = settings.arguments as Map<String,dynamic>;
回答说明
我也将此问题提交为 an issue on GitHub 并感谢 goderbauer(Flutter 团队成员)正确识别此问题并通过提供 an appropriate solution 关闭它。
戈德鲍尔说
在您的示例中,settings.arguments
的类型为 Object?
,您将其传递给 VerifyFirebaseOtpScreen.data
,后者的类型为 Map<String,dynamic>
。在空安全之前,这是合法的,被称为隐式向下转型。但是有了空安全,Dart 已经完全删除了隐式向下转换(您可以在此处阅读更多相关信息 https://dart.dev/null-safety/understanding-null-safety,只需在页面上搜索“隐式向下转换”即可)。所以现在,如果您确定 settings.arguments
是 Map<String,dynamic>
类型的行为,您需要进行显式转换,例如:settings.arguments as Map<String,dynamic>
。
他还说
(一旦我们将它们迁移到空安全,页面上的示例也必须更新)
dart.dev 解释和示例
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);
}
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