（Flutter Futurebuilder）页面更改后，应用栏标题不会立即加载

Question

import 'dart:convert';
import 'package:flutter/widgets.dart';
import 'package:flutter_app/home_page.dart';
import 'package:flutter_app/login_page.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:http/http.dart' as http;
import 'package:shared_preferences/shared_preferences.dart';
import 'package:geolocator/geolocator.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}


class _HomePageState extends State<HomePage> {
String name;
  @override
  void initState() {
    super.initState();
  }

Future <void>loadPref()async{
  SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
  return Future.delayed(Duration(seconds: 1),(){
    return name=sharedPreferences.getString("useFullName");
  });

}


logout()async{
  SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
  sharedPreferences.clear();
  sharedPreferences.commit();
  Navigator.of(context).pushAndRemoveUntil(MaterialPageRoute(builder: (BuildContext context) => LoginPage()), (Route<dynamic> route) => false);
}


 var locationMessege= "";

  void getCurrentLocation()async{
    var position = await Geolocator.getCurrentPosition(desiredAccuracy: LocationAccuracy.high);
    var lastPosition=await Geolocator.getLastKnownPosition();
    print(lastPosition);

    setState(() {
      locationMessege="$position.latitude,$position.longitude";
    });
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor:Colors.orangeAccent,
        title: FutureBuilder(
          future: loadPref(),
          builder: (context, snapshot) {
            if(name==null){
              return Text("Loading");
            }else{
              return Text("$name");
            }
          },
        ),
        actions: <Widget>[
          FlatButton(
            onPressed: () {
              logout();
            },
            child: Text("Log Out", style: TextStyle(color: Colors.white)),
          ),
        ],
      ),
      body: Container(
        decoration: BoxDecoration(
            image: DecorationImage(
                image: AssetImage("assets/bg1.png"), fit: BoxFit.cover)),
        child: Center(
          child: Container(
            padding: EdgeInsets.all(30),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [

                Column(
                  children:<Widget>  [
                    Container(
                        width: 130.0,
                        height: 130.0,
                        decoration: BoxDecoration(
                            image: DecorationImage(
                                image: AssetImage("assets/solalogo2.png"), fit: BoxFit.cover))
                    ),
                    Text("GPS Location",style: TextStyle(
                        color: Colors.black,
                        fontSize: 30.0,
                        fontWeight: FontWeight.bold)),
                    Icon(Icons.location_on,
                    size: 46,
                    color: Colors.yellow,),

                    Text("Position:$locationMessege",style:TextStyle(
                        color: Colors.black,
                        fontSize: 20.0,
                        fontWeight: FontWeight.bold)),
                    FlatButton(onPressed:(){
                      getCurrentLocation();
                    },
                    color: Colors.orange,
                        child: Text("Get New Location",
                        style: TextStyle(
                          color: Colors.black,
                        ),))
                  ],
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

成功登录后，它被定向到这个主页。我想在appbar 标题上加载用户名，但它总是触发加载语句并且在我关闭应用程序并再次加载之前不加载名称。当您重新打开应用程序时，如果用户之前登录，您将被定向到主页。我是 Flutter 的新手，这是我使用它的第二周，任何有用的提示和建议将不胜感激。

Answer 1

恕我直言，在您的情况下使用 FutureBuilder 有点矫枉过正。

您可以使用then 方法代替await。见https://api.flutter.dev/flutter/dart-async/Future/then.html。

所以，像以下代码一样更改您的initState()：

class _HomePageState extends State<HomePage> {
  String name = ""; // Defaulting to empty 
 
  @override
  void initState() {
    super.initState();

    SharedPreferences.getInstance().then((res) {
      setState(() {
        // Return string of "useFullName"
        // or return empty string if "userFullName" is null
        name = res.getString("useFullName")?? '';
      });
    });
  }
}

现在，您可以简单地将 name 变量用于您的 AppBar 标题：

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(
      backgroundColor:Colors.orangeAccent,
      title: Text(name),
    ),

    ...
  );
}

Answer 2

更改loadPref()方法的代码

Future <String> loadPref()async{
  SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
  return await sharedPreferences.getString("useFullName");

}

---

        FutureBuilder(
          future: loadPref(),
          builder: (context, snapshot) {
            if(snapshot.hasData){
              return Text("${snapshot.data}");
            }else{
              return Text("Loading");
            }
          },
        )

Answer 3

  Future <String> loadPref()async{
SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
return Future.delayed(Duration(seconds: 1),()async{
  return await sharedPreferences.getString("useFullName");
});

}

延迟包装返回使其工作，但我完全不知道为什么它现在工作但之前没有工作，并且归功于 Priyesh 建议的代码，我修改了它以使其运行。如果有人知道为什么它不起作用，请告诉我！谢谢。