[英]Updating a Stateless Widget from a Stateful Widget
主.dart:
import 'package:flutter/material.dart';
import 'package:mypackage/widgets/home_widget.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: "My App",
theme: ThemeData(primarySwatch: Colors.blueGrey),
home: Home(),
);
}
}
主頁.dart:
import 'package:flutter/material.dart';
import 'package:mypackage/widgets/secondary_page.dart';
import 'package:mypackage/widgets/home_view.dart';
import 'package:mypackage/widgets/settings_page.dart';
class Home extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return _HomeState();
}
}
class _HomeState extends State<Home> {
int currentPageIndex = 0;
final List<Widget> pageWidgets = [HomeView(), SecondaryPage(), SettingsPage()];
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("My App"),
centerTitle: true,
),
body: pageWidgets[currentPageIndex],
bottomNavigationBar: BottomNavigationBar(
onTap: onTabTapped,
currentIndex: currentPageIndex,
items: [
BottomNavigationBarItem(
icon: new Icon(Icons.home), label: "Tab One"),
BottomNavigationBarItem(
icon: new Icon(Icons.account_balance), label: "Tab Two"),
BottomNavigationBarItem(
icon: new Icon(Icons.settings), label: "Tab Three"),
],
),
floatingActionButton: FloatingActionButton(onPressed: () {
// Update data from here
HomeView().updateDisplay();
}));
}
// Changes the index when the tapped page has loaded
void onTabTapped(int index) {
setState(() {
currentPageIndex = index;
});
}
}
主頁查看.dart:
import 'package:flutter/material.dart';
import 'package:mypackage/models/mydisplay.dart';
import 'package:mypackage/network/mydata.dart';
class HomeView extends StatelessWidget {
final List<MyDisplay> dataList = [
new MyDisplay("Sample Display",
"SampleFile", 0),
];
Future<void> updateDisplay() async {
MyData myData = new MyData();
dataList.forEach((d) async {
d.changePercentage = await myData
.getDataPercentage("assets/data/" + d.fileName + ".xml");
print(d.dataName +
" change percentage: " +
d.changePercentage.toString() +
"%");
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
body: new ListView.builder(
itemCount: dataList.length,
itemBuilder: (BuildContext context, int index) =>
buildCard(context, index)),
);
}
Widget buildCard(BuildContext context, int index) {
return Container(
child: Card(
color: Colors.teal.shade200,
child: Padding(
padding: const EdgeInsets.all(25),
child: Column(children: <Widget>[
Text(dataList[index].dataName,
style: new TextStyle(
fontSize: 20, fontWeight: FontWeight.bold)),
Text(dataList[index].changePercentage.toString() + "%")
]))));
}
}
當我從 floatingActionButton 調用 updateDisplay() 方法時,它按預期工作,數據被打印到控制台,但是它似乎沒有更新實際的 UI,卡片的內容,它們只是保持在初始設置值.
澄清一下:如何從有狀態小部件更新列表視圖內(無狀態小部件內)的卡片內容?
如果這是一個重復的問題,我很抱歉,我已經查看並繼續尋找問題的答案,但我根本無法讓它工作。
您需要使用有狀態小部件,因為您無法更新無狀態小部件。 查看此鏈接以獲取更多信息。下一個問題,調用它,可以通過使用 globalKeys 來修復。 唯一奇怪的是,您必須將 Home 有狀態小部件和 HomeView 有狀態小部件保存在同一個 dart 文件中。 . 試試這個代碼讓它工作。
主頁視圖
import 'package:flutter/material.dart';
import 'package:mypackage/widgets/secondary_page.dart';
import 'package:mypackage/widgets/settings_page.dart';
import 'package:mypackage/models/mydisplay.dart';
import 'package:mypackage/network/mydata.dart';
class Home extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return _HomeState();
}
}
class _HomeState extends State<Home> {
int currentPageIndex = 0;
final List<Widget> pageWidgets = [HomeView(), SecondaryPage(), SettingsPage()];
GlobalKey<_HomeViewState> _myKey = GlobalKey();// We declare a key here
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("My App"),
centerTitle: true,
),
body: pageWidgets[currentPageIndex],
bottomNavigationBar: BottomNavigationBar(
onTap: onTabTapped,
currentIndex: currentPageIndex,
items: [
BottomNavigationBarItem(
icon: new Icon(Icons.home), label: "Tab One"),
BottomNavigationBarItem(
icon: new Icon(Icons.account_balance), label: "Tab Two"),
BottomNavigationBarItem(
icon: new Icon(Icons.settings), label: "Tab Three"),
],
),
floatingActionButton: FloatingActionButton(onPressed: () {
// Update data from here
_myKey.currentState.updateDisplay();//This is how we call the function
}));
}
// Changes the index when the tapped page has loaded
void onTabTapped(int index) {
setState(() {
currentPageIndex = index;
});
}
}
class HomeView extends StatefulWidget {
Function updateDisplay;
HomeView({Key key}): super(key: key);//This key is what we use
@override
_HomeViewState createState() => _HomeViewState();
}
class _HomeViewState extends State<HomeView> {
final List<MyDisplay> dataList = [
new MyDisplay("Sample Display",
"SampleFile", 0),
];
@override
void initState(){
super.initState();
widget.updateDisplay = () async {
MyData myData = new MyData();
dataList.forEach((d) async {
d.changePercentage = await myData
.getDataPercentage("assets/data/" + d.fileName + ".xml");
print(d.dataName +
" change percentage: " +
d.changePercentage.toString() +
"%");
});
setState((){});//This line rebuilds the scaffold
};
}
@override
Widget build(BuildContext context) {
return Scaffold(
body: new ListView.builder(
itemCount: dataList.length,
itemBuilder: (BuildContext context, int index) =>
buildCard(context, index)),
);
}
Widget buildCard(BuildContext context, int index) {
return Container(
child: Card(
color: Colors.teal.shade200,
child: Padding(
padding: const EdgeInsets.all(25),
child: Column(children: <Widget>[
Text(dataList[index].dataName,
style: new TextStyle(
fontSize: 20, fontWeight: FontWeight.bold)),
Text(dataList[index].changePercentage.toString() + "%")
]))));
}
}
我們使用 setState((){}) 來重建小部件。 只要記住一個想法。 無論您在哪里使用 updateDisplay 方法,都不要讓它在重建后循環運行。 例如。 您在孩子內部的未來構建器中使用它。 這樣它將繼續重建
編輯
我們向 HomeView 添加了一個鍵,現在我們可以像_myKey.currentState.yourFunction
一樣使用該鍵。 希望我有所幫助
雖然我了解您希望實現的目標,但我相信這將違背“Flutter 方式”。 您可以使用一個鍵來實現您想要的結果,但我相信將 state 提升到小部件樹上會更容易和更慣用。 您可以在此處的文檔中閱讀有關它的信息。
因此,在您的情況下,您可以將其更改為:
class Home extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return _HomeState();
}
}
class _HomeState extends State<Home> {
int currentPageIndex = 0;
// Added this line
List<MyDisplay> dataList = [
new MyDisplay("Sample Display",
"SampleFile", 0),
];
final List<Widget> pageWidgets;
// moved the update function from HomeView to here
Future<void> updateDisplay() async {
MyData myData = new MyData();
dataList.forEach((d) async {
d.changePercentage = await myData
.getDataPercentage("assets/data/" + d.fileName + ".xml");
print(d.dataName +
" change percentage: " +
d.changePercentage.toString() +
"%");
});
setState((){});
}
@override
Widget build(BuildContext context) {
pageWidgets = [HomeView(dataList: dataList), SecondaryPage(), SettingsPage()]
return Scaffold(
appBar: AppBar(
title: Text("My App"),
centerTitle: true,
),
body: pageWidgets[currentPageIndex],
bottomNavigationBar: BottomNavigationBar(
onTap: onTabTapped,
currentIndex: currentPageIndex,
items: [
BottomNavigationBarItem(
icon: new Icon(Icons.home), label: "Tab One"),
BottomNavigationBarItem(
icon: new Icon(Icons.account_balance), label: "Tab Two"),
BottomNavigationBarItem(
icon: new Icon(Icons.settings), label: "Tab Three"),
],
),
floatingActionButton: FloatingActionButton(onPressed: () {
updateDisplay();
}));
}
// Changes the index when the tapped page has loaded
void onTabTapped(int index) {
setState(() {
currentPageIndex = index;
});
}
}
然后對於您的 HomeView 小部件:
class HomeView extends StatelessWidget {
HomeView({this.dataList});
final List<MyDisplay> dataList;
@override
Widget build(BuildContext context) {
return Scaffold(
body: new ListView.builder(
itemCount: dataList.length,
itemBuilder: (BuildContext context, int index) =>
buildCard(context, index)),
);
}
Widget buildCard(BuildContext context, int index) {
return Container(
child: Card(
color: Colors.teal.shade200,
child: Padding(
padding: const EdgeInsets.all(25),
child: Column(children: <Widget>[
Text(dataList[index].dataName,
style: new TextStyle(
fontSize: 20, fontWeight: FontWeight.bold)),
Text(dataList[index].changePercentage.toString() + "%")
],
),
),
),
);
}
}
我還沒有測試這是否有效。 我可能稍后會。
你需要調用setState(() {});
在HomeView().updateDisplay();
更新你的 home.dart 如下。
import 'package:flutter/material.dart';
import 'package:mypackage/widgets/secondary_page.dart';
import 'package:mypackage/widgets/home_view.dart';
import 'package:mypackage/widgets/settings_page.dart';
class Home extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return _HomeState();
}
}
class _HomeState extends State<Home> {
int currentPageIndex = 0;
Widget _homeView = HomeView();
final List<Widget> pageWidgets = [_homeView, SecondaryPage(), SettingsPage()];
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("My App"),
centerTitle: true,
),
body: pageWidgets[currentPageIndex],
bottomNavigationBar: BottomNavigationBar(
onTap: onTabTapped,
currentIndex: currentPageIndex,
items: [
BottomNavigationBarItem(
icon: new Icon(Icons.home), label: "Tab One"),
BottomNavigationBarItem(
icon: new Icon(Icons.account_balance), label: "Tab Two"),
BottomNavigationBarItem(
icon: new Icon(Icons.settings), label: "Tab Three"),
],
),
floatingActionButton: FloatingActionButton(onPressed: () {
// Update data from here
_homeView.updateDisplay();
}));
}
// Changes the index when the tapped page has loaded
void onTabTapped(int index) {
setState(() {
currentPageIndex = index;
});
}
}
home_view.dart如下
import 'package:flutter/material.dart';
import 'package:mypackage/models/mydisplay.dart';
import 'package:mypackage/network/mydata.dart';
class HomeView extends StatelessWidget {
final List<MyDisplay> dataList = [
new MyDisplay("Sample Display",
"SampleFile", 0),
];
Future<void> updateDisplay() async {
MyData myData = new MyData();
dataList.forEach((d) async {
d.changePercentage = await myData
.getDataPercentage("assets/data/" + d.fileName + ".xml");
print(d.dataName +
" change percentage: " +
d.changePercentage.toString() +
"%");
});
setState((){});
}
@override
Widget build(BuildContext context) {
return Scaffold(
body: new ListView.builder(
itemCount: dataList.length,
itemBuilder: (BuildContext context, int index) =>
buildCard(context, index)),
);
}
Widget buildCard(BuildContext context, int index) {
return Container(
child: Card(
color: Colors.teal.shade200,
child: Padding(
padding: const EdgeInsets.all(25),
child: Column(children: <Widget>[
Text(dataList[index].dataName,
style: new TextStyle(
fontSize: 20, fontWeight: FontWeight.bold)),
Text(dataList[index].changePercentage.toString() + "%")
]))));
}
}
您需要將HomeView
轉換為StatefulWidget
。
之后,您需要將updateDisplay
修改為:
Future<void> updateDisplay() async {
MyData myData = new MyData();
dataList.forEach((d) async {
d.changePercentage = await myData
.getDataPercentage("assets/data/" + d.fileName + ".xml");
print(d.dataName +
" change percentage: " +
d.changePercentage.toString() +
"%");
});
setState(() {});
}
通過調用setState (() {});
您在StatefulWidget
中調用 build 方法。
編輯
像這樣更改您的HomeView
:
class HomeView extends StatefulWidget {
final List<MyDisplay> dataList = [
new MyDisplay("Sample Display",
"SampleFile", 0),
];
Future<void> updateDisplay() async {
MyData myData = new MyData();
dataList.forEach((d) async {
d.changePercentage = await myData
.getDataPercentage("assets/data/" + d.fileName + ".xml");
print(d.dataName +
" change percentage: " +
d.changePercentage.toString() +
"%");
});
}
@override
_HomeViewState createState() => _HomeViewState();
}
class _HomeViewState extends State<HomeView> {
@override
Widget build(BuildContext context) {
return Scaffold(
body: new ListView.builder(
itemCount: widget.dataList.length,
itemBuilder: (BuildContext context, int index) =>
buildCard(context, index)),
);
}
Widget buildCard(BuildContext context, int index) {
return Container(
child: Card(
color: Colors.teal.shade200,
child: Padding(
padding: const EdgeInsets.all(25),
child: Column(children: <Widget>[
Text(widget.dataList[index].dataName,
style: new TextStyle(
fontSize: 20, fontWeight: FontWeight.bold)),
Text(widget.dataList[index].changePercentage.toString() + "%")
]))));
}
}
你的Home
是這樣的:
class Home extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return _HomeState();
}
}
class _HomeState extends State<Home> {
int currentPageIndex = 0;
HomeView _homeView = HomeView();
List<Widget> pageWidgets = [_homeView, SecondaryPage(), SettingsPage()];
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("My App"),
centerTitle: true,
),
body: pageWidgets[currentPageIndex],
bottomNavigationBar: BottomNavigationBar(
onTap: onTabTapped,
currentIndex: currentPageIndex,
items: [
BottomNavigationBarItem(
icon: new Icon(Icons.home), label: "Tab One"),
BottomNavigationBarItem(
icon: new Icon(Icons.account_balance), label: "Tab Two"),
BottomNavigationBarItem(
icon: new Icon(Icons.settings), label: "Tab Three"),
],
),
floatingActionButton: FloatingActionButton(onPressed: () {
// Update data from here
_homeView.updateDisplay();
}));
}
// Changes the index when the tapped page has loaded
void onTabTapped(int index) {
setState(() {
currentPageIndex = index;
});
}
}
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