(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，直到我关闭应用程序并再次加载它才加载名称。当你重新打开应用程序时，如果用户之前登录过，你会被引导到主页。我是新手，这是我使用它的第二周，任何有用的提示和建议都会非常感激。

Answer 1

恕我冒昧，在您的情况下使用FutureBuilder有点过头了。

可以用then方法代替await方法。参见https://api.flutter.dev/flutter/dart-async/Future/then.html。

那么，像下面的代码改变你的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，您可以简单地为AppBar使用name变量标题:

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

Answer 2

修改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");
});

}

用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，而不是以前，并赞扬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工作，请告诉我!谢谢。