我在底部导航栏中工作..但是当我尝试使用第二页时显示错误..那里（抛出另一个例外：＆＃39; package：flutter / src / widgets / framework.dart＆＃39; ：失败的断言：第3722行第12行：＆＃39; _state._element == null＆＃39;：不是真的。 ）..我的页面编码如下：
主要飞镖是
import 'package:flutter/material.dart';
import 'package:typeolx/MainPage.dart';
import 'package:typeolx/colors.dart';
import 'package:typeolx/main_bottom_nav_bar.dart';
import 'package:typeolx/chatlistpage.dart';
void main() => runApp(
new MaterialApp(
theme: buildThemeData(),
home: MainPage(),
));
ThemeData buildThemeData() {
final baseTheme = ThemeData(
fontFamily: "FiraCode",
);
return baseTheme.copyWith(
primaryColor: kPrimaryColor,
primaryColorDark: kPrimaryDark,
primaryColorLight: kPrimaryLight,
accentColor: kSecondaryColor,
bottomAppBarColor: kSecondaryDark,
buttonColor: kSecondaryColor,
sliderTheme: SliderThemeData.fromPrimaryColors(
primaryColor: kPrimaryColor,
primaryColorDark: kPrimaryDark,
primaryColorLight: kPrimaryLight,
valueIndicatorTextStyle: TextStyle(),
),
textTheme: TextTheme().copyWith(
subhead: TextStyle(
fontFamily: "SnackerComic",
)),
);
}
MainPageState mainPageState = new MainPageState();
class MainPage extends StatefulWidget {
static final String routeName = '/MainPage';
@override
MainPageState createState() => mainPageState;
}
class MainPageState extends State<MainPage>
with SingleTickerProviderStateMixin {
void _rebuild() {
setState(() {});
}
@override
Widget build(BuildContext context) {
return new Scaffold(
backgroundColor:
currentIndex == 0 ? Theme.of(context).selectedRowColor : Colors.white,
body: new SafeArea(
child:
currentIndex == 0 ? new MainScreen() : new ChatListPage(),
),
bottomNavigationBar: new MainBottomNavBar(_rebuild),
floatingActionButton:
currentIndex != 0 ? null : buildSellButton(Icons.add_a_photo, 'eytrtv'),
floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
);
}
FloatingActionButton buildSellButton(IconData icon, String text) {
return new FloatingActionButton.extended(
onPressed: () {
// TODO:
},
icon: new Icon(icon),
label: new Text(text),
);
}
}
mainPage
import 'package:flutter/material.dart';
import 'package:typeolx/view1.dart';
class MainScreen extends StatefulWidget {
@override
MainScreenState createState() => new MainScreenState();
}
class MainScreenState extends State<MainScreen> {
@override
Widget build(BuildContext context) {
return new Scaffold(
body:new Stack(
children: <Widget>[
new Container(
decoration: new BoxDecoration(
image: new DecorationImage(
image: new AssetImage("assets/shopping.jpg"),
fit: BoxFit.cover,
),
),
),
new SingleChildScrollView(
child: new Center(
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Padding(padding: const EdgeInsets.only(top: 5.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
new InkWell(
onTap: () => onProductTapped(),
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("aaa",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("cccc",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
],
),),
new Padding(padding: const EdgeInsets.only(top: 5.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("fffff",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("T",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
],
),),
new Padding(padding: const EdgeInsets.only(top: 5.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("Loca",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black),
),
)
],
),
),
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("titute",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
],
),),
new Padding(padding: const EdgeInsets.only(top: 5.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("Homhings",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("Lovice",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
],
),),
new Padding(padding: const EdgeInsets.only(top: 5.0),
child: new Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("obs",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
new InkWell(
onTap: () {
},
child: new Column(
children: <Widget>[
new CircleAvatar(
child: new Icon(Icons.local_offer, color: Colors.white),
backgroundColor: Colors.black,
radius: MediaQuery.of(context).orientation == Orientation.portrait
? MediaQuery.of(context).size.width / 8
: MediaQuery.of(context).size.width / 12,
),
new Padding(
padding: const EdgeInsets.only(top: 5.0),
child: new Text("Houury",
maxLines: 2,
overflow: TextOverflow.ellipsis,
style: new TextStyle(color: Colors.white, fontSize: 14.0,fontStyle: FontStyle.italic,decorationColor: Colors.black87),
),
)
],
),
),
],
),),
],
),
),
)
]
)
);
}
onProductTapped() {
setState(() {
Navigator.of(context).push(new MaterialPageRoute(
builder: (context) => new ViewOne()));
});
}
}
main_bottom_nav_bar
import 'package:flutter/material.dart';
MainBottomNavBarState mainBottomNavBarState = new MainBottomNavBarState();
int unReadMessageCount = 0;
int currentIndex = 0;
class MainBottomNavBar extends StatefulWidget {
MainBottomNavBar(this.rebuild);
final VoidCallback rebuild;
@override
MainBottomNavBarState createState() {
return mainBottomNavBarState;
}
BottomNavigationBarItem buildBottomNavigationBarItem(BuildContext context,
String title, IconData icon, bool shouldShowUnreadCount, int pos) {
return new BottomNavigationBarItem(
icon: !shouldShowUnreadCount
? new Icon(
icon,
size: 30.0,
color: currentIndex == pos
? Theme.of(context).primaryColorDark
: Theme.of(context).accentColor.withOpacity(0.7),
)
: new Stack(
children: <Widget>[
new Icon(
icon,
size: 30.0,
color: currentIndex == pos
? Theme.of(context).primaryColorDark
: Theme.of(context).accentColor.withOpacity(0.7),
),
new Positioned(
right: 0.0,
top: 0.0,
child: unReadMessageCount > 0
? new CircleAvatar(
child: new Text(
'$unReadMessageCount',
style: new TextStyle(
fontSize: 11.0, color: Colors.white),
),
backgroundColor: Colors.red,
radius: 9.0,
)
: new Container(),
),
],
),
title: new Text(title,
style: new TextStyle(
fontSize: 16.0,
fontWeight: FontWeight.w600,
color: currentIndex == pos
? Theme.of(context).primaryColorDark
: Theme.of(context).accentColor.withOpacity(0.7),
)),
);
}
}
class MainBottomNavBarState extends State<MainBottomNavBar> {
onNavItemTapped(int pos) {
currentIndex = pos;
widget.rebuild();
}
@override
Widget build(BuildContext context) {
return new BottomNavigationBar(
currentIndex: currentIndex,
onTap: (selectedPosition) => onNavItemTapped(selectedPosition),
items: <BottomNavigationBarItem>[
widget.buildBottomNavigationBarItem(
context, 'home', Icons.home, false, 0),
widget.buildBottomNavigationBarItem(
context, 'Chats', Icons.chat, true, 1),
],
);
}
}
ViewOne页面
import 'package:flutter/material.dart';
import 'package:flutter_statusbarcolor/flutter_statusbarcolor.dart';
import 'package:screentheme/screentheme.dart';
import 'package:flutter/services.dart';
import 'package:typeolx/chatlistpage.dart';
import 'package:typeolx/main_bottom_nav_bar.dart';
import 'package:typeolx/viewMain.dart';
class ViewOne extends StatefulWidget {
@override
ViewOneState createState() => new ViewOneState();
}
class ViewOneState extends State<ViewOne> with SingleTickerProviderStateMixin {
void _rebuild1() {
setState(() {});
}
@override
void initState() {
changeStatusBarColor();
super.initState();
}
changeStatusBarColor() async {
try {
await FlutterStatusbarcolor.setStatusBarColor(Colors.white);
await ScreenTheme.darkStatusBar();
} on PlatformException catch (e) {
print(e);
}
}
@override
Widget build(BuildContext context) {
return new Scaffold(
backgroundColor:
currentIndex == 0 ? Theme
.of(context)
.selectedRowColor : Colors.white,
body: new SafeArea(
child:
currentIndex == 0 ? new ViewMain() : new ChatListPage(),
),
bottomNavigationBar: new MainBottomNavBar(_rebuild1),
floatingActionButton:
currentIndex != 0 ? null : buildSellButton(Icons.add_a_photo, 'Add Post'),
floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
);
}
FloatingActionButton buildSellButton(IconData icon, String text) {
return new FloatingActionButton.extended(
onPressed: () {},
icon: new Icon(icon),
label: new Text(text),
);
}
}