Flutter 对象列表对于期间为空，并且使用延迟数据进行充值
我是Flatter的初学者，当我编写一个调用足球运动员api的应用程序，然后将他们放入名为SelectedPlayer的列表时，我遇到了一个问题。这是我的目标，在调用它们之后，它们必须显示在小部件中，如指示emptyPlayer函数 在这里我们可以看到，当这个屏幕打开时，SelectedPlayer列表仍然为空 以下是我尝试过的：Flutter 对象列表对于期间为空，并且使用延迟数据进行充值,flutter,dart,Flutter,Dart,我是Flatter的初学者，当我编写一个调用足球运动员api的应用程序，然后将他们放入名为SelectedPlayer的列表时，我遇到了一个问题。这是我的目标，在调用它们之后，它们必须显示在小部件中，如指示emptyPlayer函数 在这里我们可以看到，当这个屏幕打开时，SelectedPlayer列表仍然为空 以下是我尝试过的： class TeamDisplayView extends StatefulWidget { List<Playerr> selectedPl
class TeamDisplayView extends StatefulWidget {
List<Playerr> selectedPlayers = [];
TeamDisplayView({
Key key,
players,
selectedPlayers,
}): selectedPlayers = (selectedPlayers == null) ? new List<Playerr>.generate(16, (int index) => null) : selectedPlayers;
@override
_TeamDisplayViewState createState() => _TeamDisplayViewState();
}
class _TeamDisplayViewState extends State<TeamDisplayView> {
getClubId() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
int clubid = prefs.getInt("clubID");
print(clubid);
makePostRequest(clubid);
setState(() {
_isLoading = false;
});
print(_isLoading);
}
Future<void> makePostRequest(int clubid) async {
// set up POST request arguments
String url = '${ApiKey.url}/api/questions/getclub';
Map<String, String> headers = {"Content-type": "application/json"};
String json = '{"clubid": "' + clubid.toString() + '"}';
Response response = await post(url, headers: headers, body: json);
String res = response.body;
Map parsed = jsonDecode(res);
ClubEdit club = ClubEdit.fromJson(parsed);
setState(() {
clubName = club.data.name;
budget = club.data.price.toDouble();
points = club.data.points;
fixture = club.data.fixture;
for (var item in club.data.players) {
widget.selectedPlayers.add(Playerr(
item.id,
item.firstname,
item.lastname,
item.position,
"equipe",
item.rating,
item.appearences,
item.goals,
item.assists,
item.cleansheets,
item.redcards,
item.yellowcards));
print(item.id);
print(item.firstname);
print("selected");
}
});
for (var item in widget.selectedPlayers) {
print(item.position);
}
print("clubname" + clubName);
print("budget" + budget.toString());
print("points" + points.toString());
print("fixture" + fixture.toString());
print(_isLoading);
}
updateRequest(int userid, String email, int points, String fixtures,
String password, String name, double price, List<Playerr> players) async {
SharedPreferences prefs = await SharedPreferences.getInstance();
email = prefs.getString("userEmail");
password = prefs.getString("userPassword");
setState(() {
userid = prefs.getInt("userID");
});
// set up POST request arguments
final url = Uri.parse('${ApiKey.url}/api/questions/updateQuestion');
Map<String, String> headers = {"Content-type": "application/json"};
List<PlayerJson> pl = [];
for (var item in players) {
pl.add(PlayerJson(
id: item.playerID,
firstname: item.firstName.toString(),
lastname: item.lastName.toString(),
position: item.position.toString(),
price: item.price,
appearences: item.appearances,
goals: item.goals,
assists: item.assists,
cleansheets: item.cleanSheets,
redcards: item.redCards,
yellowcards: item.yellowCards,
image: item.image));
}
ClubJson club = ClubJson(
userid: userid,
email: email,
password: password,
name: name,
price: price,
players: pl);
var json = jsonEncode(club.toJson());
print(club.name);
print(club.name);
print(club.price);
for (var item in club.players) {
print(item.price);
}
// make POST request
Response response = await post(url, headers: headers, body: json);
// check the status code for the result
int statusCode = response.statusCode;
// this API passes back the id of the new item added to the body
String body = response.body;
print("response body" + response.body);
// var res = jsonDecode(response.body);
// if(res == "success"){
//
//Navigator.push(context, MaterialPageRoute(builder: (context)=>BodyFantasy(),),);
return response;
}
int clubid;
String clubName;
bool _isLoading = true;
double budget;
int points;
String fixture;
String _teamName = "";
Widget _saveChanges = Text("Press to save changes");
int userid;
String email;
String password;
@override
void initState() {
this.getClubId();
for (Playerr player in widget.selectedPlayers) {
if (player != null) {
budget -= player.price;
}
// print(player.price.toString());
// print(player.goals.toString());
}
print("clubname" + clubName.toString());
print("budget" + budget.toString());
print("points" + points.toString());
print("fixture" + fixture.toString());
print(_isLoading);
super.initState();
}
emptyPlayer(int index) {
Playerr player = widget.selectedPlayers[index];
Widget playerView;
if (player == null) {
playerView = Image.asset(
"Assets/shirt_blank.png",
fit: BoxFit.fitHeight,
);
} else {
playerView = Column(
children: <Widget>[
Expanded(
child: Image.asset(
player.image,
fit: BoxFit.fitHeight,
),
),
Container(
color: Colors.black,
child: Text(
player.firstName.substring(0, 1) + ". " + player.lastName,
textAlign: TextAlign.center,
softWrap: false,
overflow: TextOverflow.fade,
),
),
Container(
color: Colors.black,
child: Text("£${player.price}m", textAlign: TextAlign.center),
),
],
);
}
return Expanded(
child: InkWell(
onTap: () =>
Navigator.pushReplacement(context,
MaterialPageRoute(builder: (BuildContext context) {
return PlayerUpdateView(
selectedPlayers: widget.selectedPlayers,
playerIndex: index,
);
})),
child: Padding(
padding: EdgeInsets.only(left: 3.0, right: 3.0),
child: playerView,
)),
);
}
@override
Widget build(BuildContext context) {
return _isLoading == true
? Container(
color: Colors.white,
child: Center(
child: CircularProgressIndicator(
valueColor: AlwaysStoppedAnimation<Color>(
Color(0xFFe70066),
),
),
),
)
: WillPopScope(
onWillPop: () async => false,
child: Scaffold(
appBar: AppBar(
title: Text("Your team"),
),
body: Stack(
children: <Widget>[
Column(
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Expanded(
child: Stack(children: <Widget>[
Positioned.fill(
child: Image.asset(
"Assets/pitch.jpg",
fit: BoxFit.fitWidth,
alignment: Alignment.topLeft,
))
])),
],
),
Column(
//players
mainAxisAlignment: MainAxisAlignment.start,
children: <Widget>[
Expanded(flex: 1, child: Container()),
Expanded(
flex: 6,
child: Padding(
padding: EdgeInsets.only(left: 40.0, right: 40.0),
child: Row(
mainAxisAlignment:
MainAxisAlignment.spaceAround,
children: List.generate(
2, (index) => emptyPlayer(index)),
),
)),
Expanded(flex: 1, child: Container()),
Expanded(
flex: 6,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: List.generate(
5, (index) => emptyPlayer(index + 2)),
)),
Expanded(flex: 1, child: Container()),
Expanded(
flex: 6,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: List.generate(
5, (index) => emptyPlayer(index + 7)),
)),
Expanded(flex: 1, child: Container()),
Expanded(
flex: 6,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: List.generate(
4, (index) => emptyPlayer(index + 12)),
)),
Expanded(flex: 1, child: Container()),
Container(
color: Styles.colorAccentDark,
padding: EdgeInsets.only(left: 8.0, right: 8.0),
child: Column(
children: <Widget>[
Padding(
padding: EdgeInsets.only(top: 4.0, bottom: 4.0),
child: Row(
children: <Widget>[
Expanded(
child: Text(
"Team Name",
style: Styles.budgetLabel,
),
),
Text(
"${clubName}",
style: Styles.budgetLabel,
)
],
),
),
Padding(
padding: EdgeInsets.only(top: 4.0, bottom: 4.0),
child: Row(
children: <Widget>[
Expanded(
child: Text(
"Fixture",
style: Styles.budgetLabel,
),
),
Text(
"${fixture}",
style: Styles.budgetLabel,
)
],
),
),
Padding(
padding: EdgeInsets.only(top: 4.0, bottom: 4.0),
child: Row(
children: <Widget>[
Expanded(
child: Text(
"Remaining Budget",
style: Styles.budgetLabel,
),
),
Text(
"£${budget}m",
style: Styles.budgetLabel,
)
],
),
),
Padding(
padding: EdgeInsets.only(top: 4.0, bottom: 4.0),
child: Row(
children: <Widget>[
Expanded(
child: Text(
"Points",
style: Styles.budgetLabel,
),
),
Text(
"${points}",
style: Styles.budgetLabel,
)
],
),
),
/* Padding(
padding: EdgeInsets.only(top: 4.0, bottom: 4.0),
child: Column(
children: <Widget>[
Expanded(
child: Text("Next Fixture", style: Styles.budgetLabel,),
),
Text("yyy", style: Styles.budgetLabel,)
],
),
),*/
],
),
),
new MaterialButton(
height: 50.0,
minWidth: double.infinity,
color: Styles.colorButton,
splashColor: Colors.teal,
textColor: Colors.white,
child: _saveChanges,
onPressed: () {
if (widget.selectedPlayers.length == 16) {
updateRequest(
userid,
"dhya@hotmail.com",
20,
"22",
"password",
"name",
25.0,
widget.selectedPlayers);
}
}),
],
),
],
)));
}
}
class TeamDisplayView扩展了StatefulWidget{
列出所选玩家=[]；
TeamDisplayView({
关键点，
球员们，
精选球员，
})：selectedPlayers=（selectedPlayers==null）？新建列表。生成（16，（int索引）=>null）：selectedPlayers；
@凌驾
_TeamDisplayViewState createState（）=>\u TeamDisplayViewState（）；
}
类_TeamDisplayViewState扩展状态{
getClubId（）异步{
SharedReferences prefs=等待SharedReferences.getInstance（）；
int clubid=prefs.getInt（“clubid”）；
印刷品（clubid）；
makePostRequest（clubid）；
设置状态（）{
_isLoading=false；
});
打印（卸载）；
}
未来makePostRequest（int-clubid）异步{
//设置请求后参数
字符串url='${ApiKey.url}/api/questions/getclub'；
映射头={“内容类型”：“应用程序/json”}；
字符串json='{“clubid”：“'+clubid.toString（）+'”}”；
Response-Response=wait-post（url，headers:headers，body:json）；
String res=response.body；
Map parsed=jsonDecode（res）；
ClubEdit club=ClubEdit.fromJson（已解析）；
设置状态（）{
clubName=club.data.name；
budget=club.data.price.toDouble（）；
积分=club.data.points；
fixture=club.data.fixture；
for（club.data.players中的var项）{
widget.selectedPlayers.add（Playerr(
项目编号：，
item.firstname，
item.lastname，
项目.职位，
“装备”，
项目1.评级，
项目1.外观，
项目1.目标，
项目1.协助，
项目1.清洁表，
项目1.红色卡片，
项目:黄卡);；
打印（项目id）；
打印（项目名称）；
打印（“选定”）；
}
});
for（widget.selectedPlayers中的变量项）{
打印（项目位置）；
}
打印（“clubname”+clubname）；
打印（“budget”+budget.toString（））；
打印（“points”+points.toString（））；
打印（“fixture”+fixture.toString（））；
打印（卸载）；
}
updateRequest（int userid、字符串电子邮件、int points、字符串fixture、，
字符串密码、字符串名称、双倍价格、列表播放器）异步{
SharedReferences prefs=等待SharedReferences.getInstance（）；
email=prefs.getString（“userEmail”）；
password=prefs.getString（“userPassword”）；
设置状态（）{
userid=prefs.getInt（“userid”）；
});
//设置请求后参数
final url=Uri.parse（'${ApiKey.url}/api/questions/updateQuestion'）；
映射头={“内容类型”：“应用程序/json”}；
列表pl=[]；
for（玩家中的var项目）{
pl.add（PlayerJson）(
id:item.playerID，
firstname:item.firstname.toString（），
lastname:item.lastname.toString（），
位置：item.position.toString（），
价格：item.price，
外观：项。外观，
目标：item.goals，
助攻：项目。助攻，
cleansheets:item.cleansheets，
redcards:item.redcards，
yellowcards:item.yellowcards，
图像：item.image）；
}
ClubJson club=ClubJson(
userid:userid，
电邮:电邮,，
密码：密码，
姓名:姓名,，
价格：价格，
玩家：pl）；
var json=jsonEncode（club.toJson（））；
打印（俱乐部名称）；
打印（俱乐部名称）；
打印（俱乐部价格）；
用于（俱乐部球员中的var项目）{
打印（项目价格）；
}
//发帖
Response-Response=wait-post（url，headers:headers，body:json）；
//检查结果的状态代码
int statusCode=response.statusCode；
//此API传回添加到主体的新项的id
字符串体=response.body；
打印（“响应正文”+响应正文）；
//var res=jsonDecode（response.body）；
//如果（res==“成功”）{
//
//push（context，MaterialPageRoute（builder:（context）=>BodyFantasy（），）；
返回响应；
}
国际俱乐部；
字符串clubName；
bool_isLoading=true；
双重预算；
积分；
线夹具；
字符串_teamName=“”；
小部件_saveChanges=文本（“按以保存更改”）；
int用户标识；
字符串电子邮件；
字符串密码；
@凌驾
void initState（）{
这个.getClubId（）；
for（小部件中的Playerr播放器。selectedPlayers）{
如果（玩家！=null）{
预算-=玩家价格；
}
//打印（player.price.toString（））；
//打印（player.goals.toString（））；
}
打印（“clubname”+clubname.toString（））；
打印（“budget”+budget.toString（））；
打印（“points”+points.toString（））；
打印（“fixture”+fixture.toString（））；
打印（卸载）；
super.initState（）；
}
空层（整数索引）{
Playerr player=widget.selectedPlayers[index]；
小部件playerView；
if（player==null）{
playerView=Image.asset(
“Assets/shirt_blank.png”，
适合度：BoxFit.fit高度，
);
}否则{
playerView=列(
儿童：[
扩大(
子：Image.asset(
player.image，
适合度：BoxFit.fit高度，
),
),
容器(
颜色：颜色，黑色，
子：文本(
player.firstName.substring（0，1）+“+player.lastName，
textAlign:textAlign.center，
软包装：错误，
溢出：TextOverflow.fade，
),
),
容器(
颜色：颜色，黑色，
子项：Text（£${player.price}m），textAlign:textAlign.center），
I/zygote ( 6982): Background concurrent copying GC freed 4231(210KB) AllocSpace objects, 24(1248KB) LOS objects, 55% free, 1211KB/2MB, paused 7.463ms total 20.500ms
I/flutter ( 6982): clubnamenull
I/flutter ( 6982): budgetnull
I/flutter ( 6982): pointsnull
I/flutter ( 6982): fixturenull
I/flutter ( 6982): false
I/flutter ( 6982): clubnamenull
I/flutter ( 6982): budgetnull
I/flutter ( 6982): pointsnull
I/flutter ( 6982): fixturenull
I/flutter ( 6982): true
D/EGL_emulation( 6982): eglMakeCurrent: 0xe9204780: ver 2 0 (tinfo 0xe9203c60)
I/flutter ( 6982): 1
I/flutter ( 6982): false
I/flutter ( 6982): 19827
I/flutter ( 6982): Joshua Jon
I/flutter ( 6982): selected
I/flutter ( 6982): 1438
I/flutter ( 6982): Bernd
I/flutter ( 6982): selected
I/flutter ( 6982): 657
I/flutter ( 6982): Kenny Joelle
I/flutter ( 6982): selected
I/flutter ( 6982): 18893
I/flutter ( 6982): Federico
I/flutter ( 6982): selected
I/flutter ( 6982): 629
I/flutter ( 6982): Kevin
I/flutter ( 6982): selected
I/flutter ( 6982): 49923
I/flutter ( 6982): Aboubakar
I/flutter ( 6982): selected
I/flutter ( 6982): 904
I/flutter ( 6982): Paul
I/flutter ( 6982): selected
I/flutter ( 6982): 18918
I/flutter ( 6982): Charlie
I/flutter ( 6982): selected
I/flutter ( 6982): 20619
I/flutter ( 6982): Illan
I/flutter ( 6982): selected
I/flutter ( 6982): 889
I/flutter ( 6982): Victor
I/flutter ( 6982): selected
I/flutter ( 6982): 2806
I/flutter ( 6982): Fabian Lukas
I/flutter ( 6982): selected
I/flutter ( 6982): 18945
I/flutter ( 6982): Stuart
I/flutter ( 6982): selected
I/flutter ( 6982): 1826
I/flutter ( 6982): Sébastien
I/flutter ( 6982): selected
I/flutter ( 6982): 12975
I/flutter ( 6982): Odion Jude
I/flutter ( 6982): selected
I/flutter ( 6982): 19027
I/flutter ( 6982): Neeskens
I/flutter ( 6982): selected
I/flutter ( 6982): 2678
I/flutter ( 6982): Diogo José
I/flutter ( 6982): selected
E/flutter ( 6982): [ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: NoSuchMethodError: The getter 'position' was called on null.
E/flutter ( 6982): Receiver: null
E/flutter ( 6982): Tried calling: position
E/flutter ( 6982): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
E/flutter ( 6982): #1 _TeamDisplayViewState.makePostRequest (package:footyappp/Fantazyy/team_display_view.dart:83:18)
E/flutter ( 6982): <asynchronous suspension>
E/flutter ( 6982): #2 _TeamDisplayViewState.getClubId (package:footyappp/Fantazyy/team_display_view.dart:35:5)
E/flutter ( 6982): <asynchronous suspension>
E/flutter ( 6982): #3 _TeamDisplayViewState.initState (package:footyappp/Fantazyy/team_display_view.dart:168:10)
E/flutter ( 6982): #4 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4765:58)
E/flutter ( 6982): #5 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4601:5)
E/flutter ( 6982): #6 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #7 Element.updateChild (package:flutter/src/widgets/framework.dart:3327:18)
E/flutter ( 6982): #8 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6118:14)
E/flutter ( 6982): #9 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #10 Element.updateChild (package:flutter/src/widgets/framework.dart:3327:18)
E/flutter ( 6982): #11 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
E/flutter ( 6982): #12 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
E/flutter ( 6982): #13 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4606:5)
E/flutter ( 6982): #14 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4601:5)
E/flutter ( 6982): #15 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #16 Element.updateChild (package:flutter/src/widgets/framework.dart:3327:18)
E/flutter ( 6982): #17 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6118:14)
E/flutter ( 6982): #18 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #19 Element.updateChild (package:flutter/src/widgets/framework.dart:3327:18)
E/flutter ( 6982): #20 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6118:14)
E/flutter ( 6982): #21 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #22 Element.updateChild (package:flutter/src/widgets/framework.dart:3327:18)
E/flutter ( 6982): #23 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
E/flutter ( 6982): #24 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
E/flutter ( 6982): #25 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
E/flutter ( 6982): #26 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4606:5)
E/flutter ( 6982): #27 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4791:11)
E/flutter ( 6982): #28 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4601:5)
E/flutter ( 6982): #29 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #30 Element.updateChild (package:flutter/src/widgets/framework.dart:3327:18)
E/flutter ( 6982): #31 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6118:14)
E/flutter ( 6982): #32 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #33 Element.updateChild (package:flutter/src/widgets/framework.dart:3327:18)
E/flutter ( 6982): #34 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6118:14)
E/flutter ( 6982): #35 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #36 Element.updateChild (package:flutter/src/widgets/framework.dart:3327:18)
E/flutter ( 6982): #37 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4652:16)
E/flutter ( 6982): #38 StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:4800:11)
E/flutter ( 6982): #39 Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)
E/flutter ( 6982): #40 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4606:5)
E/flutter ( 6982): #41 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:4791:11)
E/flutter ( 6982): #42 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4601:5)
E/flutter ( 6982): #43 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3569:14)
E/flutter ( 6982): #44 Element.updateChild (