我想在main中判断启动哪个页面(其实是登录页面和首页)。所以我必须阅读首选项中的 isLogin 。如何在 main 中做到这一点?
我绑定(bind)了这些代码:
Future<Null> checkIsLogin() async {
String _token = "";
// If token exist already, then HomePage
SharedPreferences prefs = await SharedPreferences.getInstance();
_token = prefs.getString("token");
print('get token from prefs: ' + _token);
if (_token != "" && _token != null) {
// already login
print("alreay login.");
isLogin = true;
}
}
void main() {
App.init();
// if we have token then go to HomePage directly otherwise go to LoginPage.
Widget _defaultHome = new LoginPage();
checkIsLogin();
if (isLogin) {
_defaultHome = new HomePage();
}
runApp(new MaterialApp(
debugShowCheckedModeBanner: false,
theme: globalThemeData,
home: _defaultHome
));
}
在上面的代码中,isLogin 是一个全局变量。出现错误:
Performing full restart...
Restarted app in 2,810ms.
[VERBOSE-2:dart_error.cc(16)] Unhandled exception:
Invalid argument(s)
#0 _StringBase.+ (dart:core/runtime/libstring_patch.dart:245:57)
#1 checkIsLogin (file:///Volumes/xs/awesome/uranus/clients/flutter/flutter_asgard/lib/main.dart:17:34)
<asynchronous suspension>
#2 main (file:///Volumes/xs/awesome/uranus/clients/flutter/flutter_asgard/lib/main.dart:29:3)
#3 _startIsolate.<anonymous closure> (dart:isolate/runtime/libisolate_patch.dart:279:19)
#4 _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:165:12)
似乎在 main 中调用 async 有问题,如何让它工作?
最佳答案
这就是我所做的,
void main() {
WidgetsFlutterBinding.ensureInitialized();
SharedPreferences.getInstance().then((instance) {
StorageService().sharedPreferencesInstance = instance; // Storage service is a service to manage all shared preferences stuff. I keep the instance there and access it whenever i wanted.
runApp(MyApp());
});
}
然后在Material App Build中
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'App Title',
home: _checkUserLoggedIn()
? HomeScreen()
: LoginPage(),
);
}
_checkUserLoggedIn 函数
bool _checkUserLoggedIn() {
return _storageService.getFromShared('isLoggedIn'); // Just a get method from shared preferences
}
关于async-await - Flutter 在 main 中读取共享首选项,然后决定哪个启动页面?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/50458526/