Flutter Future<bool> 与 bool 类型

Question

我的 Flutter 项目有一个 utility.dart 文件和一个 main.dart 文件。我调用 main.dart 文件中的函数，但它有问题。它总是显示警报“OK”，我认为问题是实用程序类 checkConnection() 返回了一个未来的 bool 类型。

main.dart：

if (Utility.checkConnection()==false) {
  Utility.showAlert(context, "internet needed");
} else {
  Utility.showAlert(context, "OK");
} 

utility.dart：

import 'package:flutter/material.dart';
import 'package:connectivity/connectivity.dart';
import 'dart:async';

class Utility {


  static Future<bool> checkConnection() async{

    ConnectivityResult connectivityResult = await (new Connectivity().checkConnectivity());

    debugPrint(connectivityResult.toString());

    if ((connectivityResult == ConnectivityResult.mobile) || (connectivityResult == ConnectivityResult.wifi)){
      return true;
    } else {
      return false;
    }
  }

  static void showAlert(BuildContext context, String text) {
    var alert = new AlertDialog(
      content: Container(
        child: Row(
          children: <Widget>[Text(text)],
        ),
      ),
      actions: <Widget>[
        new FlatButton(
            onPressed: () => Navigator.pop(context),
            child: Text(
              "OK",
              style: TextStyle(color: Colors.blue),
            ))
      ],
    );

    showDialog(
        context: context,
        builder: (_) {
          return alert;
        });
  }
}

Answer 1

您需要从Future<bool> 中取出bool。使用可以then block或await。

用 then 块

_checkConnection() {
  Utiliy.checkConnection().then((connectionResult) {
    Utility.showAlert(context, connectionResult ? "OK": "internet needed");
  })
}

等待

_checkConnection() async {
 bool connectionResult = await Utiliy.checkConnection();
 Utility.showAlert(context, connectionResult ? "OK": "internet needed");
}

更多详情，请参考here。

Answer 2

在Future函数中你必须返回未来的结果，所以你需要改变：

return true;

收件人：

return Future<bool>.value(true);

所以具有正确返回的完整功能是：

 static Future<bool> checkConnection() async{

    ConnectivityResult connectivityResult = await (new Connectivity().checkConnectivity());

    debugPrint(connectivityResult.toString());

    if ((connectivityResult == ConnectivityResult.mobile) || (connectivityResult == ConnectivityResult.wifi)){
      return Future<bool>.value(true);
    } else {
      return Future<bool>.value(false);
    }
  }

Answer 3

我也遇到过这个问题，所以我试图通过简单的方法解决，但我不能。我试图在不同的不同页面中实现布尔值。

import 'package:connectivity_plus/connectivity_plus.dart';
class Connection{
  static String msg  = "";
  //Check Internet Connection

  static Future<bool> connection() async{
    //result = await _connectivity.checkConnectivity();
    Connectivity _connectivity = Connectivity();
    late ConnectivityResult result;
    result = await _connectivity.checkConnectivity();
    if(result == ConnectivityResult.mobile){
      //msg = "Connected with Mobile";
      return Future<bool>.value(true);
    }else if(result == ConnectivityResult.wifi){
      //msg = "Connected with WiFi";
      return Future<bool>.value(true);
    }
    else if(result == ConnectivityResult.ethernet){
     // msg = "Connected with Ethernet";
      return Future<bool>.value(true);
    }
    return Future<bool>.value(false);
  }
}

你可以用这个

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:connectivity_plus/connectivity_plus.dart';
import 'package:quizzes_application/Alert.dart';

class Connection extends StatefulWidget {
  const Connection({Key? key}) : super(key: key);

  @override
  _ConnectionState createState() => _ConnectionState();
}

class _ConnectionState extends State<Connection> {
  
  //Connection Test

  static bool isConnected = true;
  late StreamSubscription sub;
  //Internet Connectivity Check
  void initState(){
    super.initState();
    sub = Connectivity().onConnectivityChanged.listen((result) {
      setState(() {
        isConnected = (result == ConnectivityResult.none);
      });
    });
  }
  void dispose(){
    sub.cancel();
    super.dispose();
  }
  
  @override
  Widget build(BuildContext context) {
    return isConnected ? Scaffold() : Alert.alertMsg();
  }
}