我已经构建了一个脚手架屏幕，正文中有一个 PageView 和一个底部导航栏。
我还为此页面构建了 Cubit + State 管理器。
当屏幕第一次打开时，我希望触发 API 调用。我还希望选择选项卡 1（在 PageView 和 bottomNavigationBar 上）。当 API 返回响应时，我希望事件侦听器更新屏幕并选择选项卡 0。
这适用于 bottomNavigationBar，但我在更新 PageView 时遇到问题。这是我的代码：
class HomeScreen extends StatefulWidget {
@override
_HomeScreenState createState() => _HomeScreenState();
}
class _HomeScreenState extends State<HomeScreen> {
int _page = 1;
PageController _c;
double iconSize = 32;
bool forceCourseEnrolment = true;
@override
void initState() {
_c = new PageController(
initialPage: 1,
keepPage: false,
);
super.initState();
}
@override
Widget build(BuildContext context) {
return BlocConsumer<HomeScreenCubit, HomeScreenState>(
listener: (context, state) {
debugPrint("listener received something");
if (state is DataRetrieved) {
state.enrolledCourses.length > 0
? forceCourseEnrolment = false
: forceCourseEnrolment = true;
state.enrolledCourses.length > 0 ? _page = 0 : _page = 1;
var hasClients = this._c.hasClients;
debugPrint("this._c.hasClients $hasClients");
// This prints: this._c.hasClients false
// Enabling this line:
// this._c.jumpToPage(_page);
// leads to:
// [ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: 'package:flutter/src/widgets/scroll_controller.dart': Failed assertion: line 112 pos 12: '_positions.isNotEmpty': ScrollController not attached to any scroll views.
}
}, builder: (context, state) {
if (state is HomeScreenInitial) {
context.bloc<HomeScreenCubit>().retrieveData();
return Scaffold(
body: SpinKitChasingDots(
color: COLOR_main_purple,
size: 50.0,
));
}
return Scaffold(
body: PageView(
controller: _c,
onPageChanged: (newPage) {
setState(() {
this._page = newPage;
});
},
physics: NeverScrollableScrollPhysics(),
children: [
PurchasedCoursesTab(),
ElearningTab(),
MyPracticeTab(),
ProfileTab(),
],
),
bottomNavigationBar: SizedBox(
height: 80,
child: Container(
decoration: BoxDecoration(
borderRadius: BorderRadius.only(
topRight: Radius.circular(30),
topLeft: Radius.circular(30)),
boxShadow: [
BoxShadow(
color: Colors.black38.withOpacity(0.1),
spreadRadius: 0,
blurRadius: 25),
],
),
child: ClipRRect(
borderRadius: BorderRadius.only(
topLeft: Radius.circular(30.0),
topRight: Radius.circular(30.0),
),
child: BottomNavigationBar(
currentIndex: _page,
onTap: (index) {
if (forceCourseEnrolment == false) {
this._c.animateToPage(index,
duration: const Duration(milliseconds: 250),
curve: Curves.easeInOut);
}
},
type: BottomNavigationBarType.fixed,
backgroundColor: Colors.white,
items: <BottomNavigationBarItem>[
BottomNavigationBarItem(
// title: Text(""),
title: showIndicator(_page == 0),
icon: Container(
width: iconSize,
height: iconSize,
child: SvgPicture.asset('assets/images/ic_run.svg',
color: _page == 0
? COLOR_main_purple
: forceCourseEnrolment == false
? Colors.black
: COLOR_main_text_grey_with_opacity),
)),
BottomNavigationBarItem(
title: showIndicator(_page == 1),
icon: Container(
width: iconSize,
height: iconSize,
child: SvgPicture.asset(
'assets/images/ic_e_learning.svg',
color: _page == 1
? COLOR_main_purple
: Colors.black),
)),
BottomNavigationBarItem(
title: showIndicator(_page == 2),
icon: Container(
width: iconSize,
height: iconSize,
child: SvgPicture.asset(
'assets/images/ic_journal.svg',
color: _page == 2
? COLOR_main_purple
: forceCourseEnrolment == false
? Colors.black
: COLOR_main_text_grey_with_opacity),
)),
BottomNavigationBarItem(
title: showIndicator(_page == 3),
// title: Text(_page == 3 ? "•" : "", style: TextStyle(
// color: COLOR_main_purple, fontSize: 24.0)),
icon: Container(
width: iconSize,
height: iconSize,
child: SvgPicture.asset(
'assets/images/ic_gamification.svg',
color: _page == 3
? COLOR_main_purple
: forceCourseEnrolment == false
? Colors.black
: COLOR_main_text_grey_with_opacity),
)),
],
),
)),
));
});
}
}
当我尝试在 BlocConsumer 的侦听器中更改页面时遇到的错误：
[错误：flutter/lib/ui/ui_dart_state.cc(177)] 未处理的异常：'package:flutter/src/widgets/scroll_controller.dart'：断言失败：第 112 行 pos 12：'_positions.isNotEmpty'：未附加 ScrollController到任何滚动视图。