所以我在做项目时正在探索颤动。我想制作一个带有动态列表和Webview的简单新闻列表应用程序，以打开全文。但是，WebViewScaffold显示空白页。
尝试了Flutter Inspector尝试查找错误，但无法获取。尝试更改类和状态。
import 'package:flutter/material.dart';
import 'makeCard.dart';
import 'webService.dart';
import 'constants.dart';
import 'NewsArticle.dart';
import 'package:flutter_webview_plugin/flutter_webview_plugin.dart';
import 'package:http/http.dart' as http;
import 'package:http/http.dart';
import 'dart:convert';
import 'package:flutter/widgets.dart';
import 'newsDetail.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Flutter Demo',
theme: new ThemeData(primaryColor: Color.fromRGBO(58, 66, 86, 1.0)),
home: NewsList(),
);
}
}
class NewsListState extends State<NewsList> {
List<NewsArticle> _newsArticles = List<NewsArticle>();
@override
void initState() {
super.initState();
_populateNewsArticles();
}
void _populateNewsArticles() {
Webservice().load(NewsArticle.all).then((newsArticles) => {
setState(() => {_newsArticles = newsArticles})
});
}
ListTile _buildItemsForListView(BuildContext context, int index) {
return ListTile(
title: _newsArticles[index].urlToImage == null
? Image.asset(Constants.NEWS_PLACEHOLDER_IMAGE_ASSET_URL)
: Image.network(_newsArticles[index].urlToImage),
subtitle:
Text(_newsArticles[index].title, style: TextStyle(fontSize: 18)),
contentPadding: EdgeInsets.symmetric(horizontal: 10.0, vertical: 10.0),
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('News'),
),
body: new Container(
margin: const EdgeInsets.only(left: 2.0, right: 2.0),
child: new Card(
child: new ListView.separated(
separatorBuilder: (context, index) => Divider(
height: 10.0,
),
itemCount: _newsArticles.length,
itemBuilder: _buildItemsForListView,
),
),
));
}
}
class NewsList extends StatefulWidget {
@override
createState() => NewsListState();
}
class Constants {
static final String HEADLINE_NEWS_URL = 'https://newsapi.org/v2/top-headlines?country=us&apiKey=3f85510c67ef4757b65bc2cd96a9eaf9';
static final String NEWS_PLACEHOLDER_IMAGE_ASSET_URL = 'assets/placeholder.png';
}
class Resource<T> {
final String url;
T Function(Response response) parse;
Resource({this.url, this.parse});
}
class Webservice {
Future<T> load<T>(Resource<T> resource) async {
final response = await http.get(resource.url);
if (response.statusCode == 200) {
return resource.parse(response);
} else {
throw Exception('Failed to load data!');
}
}
}
class DetailPage extends StatefulWidget {
DetailPage(this.url);
final String url;
@override
createState() => DetailPageState(this.url);
}
class DetailPageState extends State<DetailPage> {
var _url;
DetailPageState(this._url);
Widget build(BuildContext context) {
return Scaffold(
appBar: new AppBar(
title: new Text(
"Full Article",
),
),
body: new Container(
child: new Column(
children: <Widget>[
MaterialApp(
routes: {
"/": (_) => new WebviewScaffold(
url: _url,
appBar: new AppBar(title: new Text("")),
hidden:true,
)
},
),
],
),
),
);
}
}
class NewsArticle {
final String url;
final String title;
final String descrption;
final String urlToImage;
final String publishedAt;
final String content;
NewsArticle({this.url,this.title, this.descrption, this.urlToImage,this.publishedAt,this.content
});
factory NewsArticle.fromJson(Map<String,dynamic> json) {
return NewsArticle(
title: json['title'],
descrption: json['description'],
urlToImage: json['urlToImage'] ?? Constants.NEWS_PLACEHOLDER_IMAGE_ASSET_URL,
url: json['url'],
publishedAt: json['publishedAt'],
content: json['content']
);
}
static Resource<List<NewsArticle>> get all => Resource(
url: Constants.HEADLINE_NEWS_URL,
parse: (response) {
final result = json.decode(response.body);
Iterable list = result['articles'];
return list.map((model) => NewsArticle.fromJson(model)).toList();
}
);
}
class NewsListState extends State<NewsList> {
List<NewsArticle> _newsArticles = List<NewsArticle>();
@override
void initState() {
super.initState();
_populateNewsArticles();
}
void _populateNewsArticles() {
Webservice().load(NewsArticle.all).then((newsArticles) => {
setState(() => {_newsArticles = newsArticles})
});
}
ListTile _buildItemsForListView(BuildContext context, int index) {
return ListTile(
title: _newsArticles[index].urlToImage == null
? Image.asset(Constants.NEWS_PLACEHOLDER_IMAGE_ASSET_URL)
: Image.network(_newsArticles[index].urlToImage),
subtitle:
Text(_newsArticles[index].title, style: TextStyle(fontSize: 18)),
contentPadding: EdgeInsets.symmetric(horizontal: 10.0, vertical: 10.0),
onTap: () {
var url = _newsArticles[index].url;
Navigator.push(context,
new MaterialPageRoute(
builder: (context) => new DetailPage(url),
));
},
);
}
Card makeCard(BuildContext context, int index) {
return Card(
elevation: 8.0,
margin: new EdgeInsets.symmetric(horizontal: 10.0, vertical: 6.0),
child: Container(
decoration: BoxDecoration(color: Color.fromRGBO(64, 75, 96, .9)),
child: _buildItemsForListView(context, index)
),
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Color.fromRGBO(58, 66, 86, 1.0),
appBar: AppBar(
elevation: 0.1,
backgroundColor: Color.fromRGBO(58, 66, 86, 1.0),
title: Text('News'),
actions: <Widget>[
IconButton(
icon: Icon(Icons.list),
onPressed: () {},
)
],
),
body: Container(
child: ListView.builder(
itemCount: _newsArticles.length,
itemBuilder: makeCard,
),
),
bottomNavigationBar: Container(
height: 55.0,
child: BottomAppBar(
color: Color.fromRGBO(58, 66, 86, 1.0),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
IconButton(
icon: Icon(Icons.home, color: Colors.white),
onPressed: () {},
),
IconButton(
icon: Icon(Icons.blur_on, color: Colors.white),
onPressed: () {},
),
IconButton(
icon: Icon(Icons.hotel, color: Colors.white),
onPressed: () {},
),
IconButton(
icon: Icon(Icons.account_box, color: Colors.white),
onPressed: () {},
)
],
),
),
),
);
}
}
class NewsList extends StatefulWidget {
@override
createState() => NewsListState();
}
The console log for the error -
D/ViewRootImpl@e393259[MainActivity]( 3890): ViewPostIme pointer 0
D/ViewRootImpl@e393259[MainActivity]( 3890): ViewPostIme pointer 1
I/flutter ( 3890): Another exception was thrown: BoxConstraints forces an infinite height.
I/flutter ( 3890): Another exception was thrown: RenderBox was not laid out: RenderStack#59935 relayoutBoundary=up8 NEEDS-PAINT
I/flutter ( 3890): Another exception was thrown: RenderBox was not laid out: _RenderTheatre#f69a8 relayoutBoundary=up7 NEEDS-PAINT
I/flutter ( 3890): Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#677d7 relayoutBoundary=up6 NEEDS-PAINT
I/flutter ( 3890): Another exception was thrown: RenderBox was not laid out: RenderAbsorbPointer#b985b relayoutBoundary=up5 NEEDS-PAINT
I/flutter ( 3890): Another exception was thrown: RenderBox was not laid out: RenderPointerListener#86c3b relayoutBoundary=up4 NEEDS-PAINT
I/flutter ( 3890): Another exception was thrown: RenderBox was not laid out: RenderCustomPaint#b0c68 relayoutBoundary=up3 NEEDS-PAINT
I/flutter ( 3890): Another exception was thrown: RenderBox was not laid out: RenderSemanticsAnnotations#c9989 relayoutBoundary=up2 NEEDS-PAINT
I/flutter ( 3890): Another exception was thrown: RenderBox was not laid out: RenderFlex#050d5 relayoutBoundary=up1 NEEDS-PAINT
I/flutter ( 3890): Another exception was thrown: NoSuchMethodError: The method '<=' was called on null.
答案 0 :(得分：0)
将此行添加到AndroidManifest.xml，然后重新启动应用程序。
步骤1：
查找{"Offset":0,"Total":0,"Results":[{"Id":1,"RefId":1,"SecondRefId":1,"ThirdRefId":111,"Name":"test1","JSON":"TEST1","JsonType":"test","Desc":"test1","AuditId":0,"AuditStamp":"\/Date(1577190306230-0000)\/"}],"Meta":{}}
文件。
文件路径： AndroidManifest.xml
第2步：
在Android >> app >> main >> AndroidManifest.xml标记
application第3步： 重新启动您的应用程序。
希望这个答案对您有所帮助：）
答案 1 :(得分：0)
另一个可能的原因是将一个小部件传递给 WebviewScaffold.bottomNavigationBar。我不知道为什么会发生这种情况，但是当我删除传递给它的小部件并将小部件传递给 WebviewScaffold.persistentFooterButtons 时，页面被呈现，我的页脚小部件被呈现。似乎传递给 bottomNavigationBar 的小部件呈现在 WebView 之上。