Flutter:“未来<动态>"不是布尔型的子类型 [英] Flutter : 'Future <dynamic>' is not a subtype of type bool

问题描述

我正在尝试实现简单的登录/注销功能.我的情况是这样的:

I was trying to implement a simple login/logout functionality. My scenario is this:

我有2个页面(登录页面和主页)，在main.dart中，我正在使用SharedPreferences来检查用户是否已经登录，如果用户已登录，则将布尔值设置为true单击一个按钮.

I have 2 pages ( login page and home page), In the main.dart, I am using SharedPreferences to check if a user has already logged in or not if the user is logged in, I set a boolean value as true on click of a button.

我遇到的问题是，我创建了一个routeLogin函数，以在主页和着陆页之间进行选择. 我得到这个错误:

The issue I am having is, I have a routeLogin function that I created to choose between Homepage and Landingpage. And I get this error:

I/flutter(9026):W小部件库引起的异常CA ═══════════════════════════════ I/flutter(9026):构建MyApp(dirty)时引发了以下断言: I/flutter(9026):类型'Future'不是类型'bool'的子类型 I/颤振(9026): I/flutter(9026):要么断言表明框架本身有错误，要么我们应该提供 I/flutter(9026):此错误消息中的更多信息可帮助您确定和解决根本原因. I/flutter(9026):无论哪种情况，请通过在GitHub上提交错误来报告此断言: I/flutter(9026): https://github.com/flutter /flutter/issues/new?template=BUG.md

I/flutter ( 9026): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ I/flutter ( 9026): The following assertion was thrown building MyApp(dirty): I/flutter ( 9026): type 'Future' is not a subtype of type 'bool' I/flutter ( 9026): I/flutter ( 9026): Either the assertion indicates an error in the framework itself, or we should provide substantially I/flutter ( 9026): more information in this error message to help you determine and fix the underlying cause. I/flutter ( 9026): In either case, please report this assertion by filing a bug on GitHub: I/flutter ( 9026): https://github.com/flutter/flutter/issues/new?template=BUG.md

这是我的代码:

import 'package:credit/src/pages/landing.dart';
import 'package:flutter/material.dart';
import 'package:credit/src/pages/credit/home.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.

 bool checkValue;
 checkLoginValue () async{
   SharedPreferences loginCheck = await SharedPreferences.getInstance();
   checkValue = loginCheck.getBool("login");
   }
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Test App',
       debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: routeLogin());
      //home: LandingPage());      
  }

  routeLogin()
  {
    print("Check value");
    if (checkValue == null){
      return LandingPage();
    }
    else{
      return HomePage();
    }

  }
}

请让我知道我哪里出了问题，我是Flutter的新手.

Please let me know where did I went wrong, I am new to Flutter.

推荐答案

您可以使用以后的构建器轻松获得此行为.

you can use future builder to obtain this behavior easily.

Future<bool> checkLoginValue () async{
   SharedPreferences loginCheck = await SharedPreferences.getInstance();
   return loginCheck.getBool("login");
   }

  @override
  Widget build(BuildContext context) {

    return MaterialApp(
      title: 'Test App',
       debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home:FutureBuilder<bool>(
            future: checkLoginValue,
             builder:(BuildContext context, AsyncSnapshot<bool> snapshot){
           if (snapshot.data == false){
                    return LandingPage();
    }
    else{
      return HomePage();
    }
}
);

  }

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