以下代码几乎是来自底部导航栏的官方flutter github示例的复制粘贴。问题是,在包含视图的窗口小部件打开时,所有内容都被预加载。每次按下底栏元素时,我都会重新加载所有视图。换句话说,当我按下第一个项目时,日志显示其他人(第二个和第三个)正在进行网络呼叫。当我按下第二个时,日志显示即使是第一个正在进行网络呼叫。当我调试时,我发现每次从底栏选择一个小部件时,包含它的小部件都会重建(有一个方法调用buid)。这是正常的行为吗?这是包含小部件的代码
class MainScreen extends StatefulWidget{
@override
State<StatefulWidget> createState()=> MainScreenState();
}
class MainScreenState extends State<MainScreen> with TickerProviderStateMixin{
GlobalKey<ScaffoldState> scaffoldState = new GlobalKey();
int _currentSelection = 0;
BottomNavigationBarType _navigationBarType = BottomNavigationBarType.fixed;
Li
st<NavigationIconView> _navigationIcons;
@override
void initState() {
super.initState();
_navigationIcons = <NavigationIconView>[
new NavigationIconView(
icon: const Icon(Icons.home),
title: 'Главная',
vsync: this
),
new NavigationIconView(
icon: const Icon(Icons.map),
title: 'Квесты',
vsync: this
),
new NavigationIconView(
icon: const Icon(Icons.dehaze),
title: 'Профиль',
vsync: this
)
];
for(NavigationIconView v in _navigationIcons)
v.controller.addListener(_rebuild);
_navigationIcons[_currentSelection].controller.value = 1.0;
}
@override
void dispose() {
for(NavigationIconView v in _navigationIcons)
v.controller.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
final BottomNavigationBar botNavBar = new BottomNavigationBar(
items: _navigationIcons
.map((NavigationIconView navigationView) => navigationView.item)
.toList(),
currentIndex: _currentSelection,
fixedColor: Colors.green,
type: _navigationBarType,
onTap: (int index) {
setState(() {
_navigationIcons[_currentSelection].controller.reverse();
_currentSelection = index;
_navigationIcons[_currentSelection].controller.forward();
print('pressed : $_currentSelection');
});
},
);
return new Scaffold(
key: scaffoldState,
body: new Center(
key: new Key('Main view container'),
child: new FutureBuilder<Widget>(
future: _buildTransitionsStack(),
builder: (BuildContext context, AsyncSnapshot<Widget> snapshot){
if(!snapshot.hasError) return snapshot.data;
else{
print('sh3t happened in main : ${snapshot.error}');
}
}
),
),
bottomNavigationBar: botNavBar,
);
}
Future<Widget> _buildTransitionsStack() {
final List<FadeTransition> transitions = <FadeTransition>[];
return _showMain().then((mainWidget){
transitions.add(_navigationIcons[0]
.transition(_navigationBarType,mainWidget, context));
print('size ${transitions.length}');
}).then((_){
transitions.add(_navigationIcons[1].transition(_navigationBarType,
_showQuest(), context));
transitions.add(_navigationIcons[2].transition(_navigationBarType,
_showProfile(), context));
transitions.sort((FadeTransition a, FadeTransition b) {
final Animation<double> aAnimation = a.opacity;
final Animation<double> bAnimation = b.opacity;
final double aValue = aAnimation.value;
final double bValue = bAnimation.value;
return aValue.compareTo(bValue);
});
return new Stack(children: transitions);
});
}
Future<Widget> _showMain(){
return _getToken().then((token){
return new FeedView(token);
});
}
Widget _showQuest(){
// return DetailableListScreen(ViewModelType.QUEST);
return new QuestScreen();
}
Widget _showProfile(){
return new Text('profile');
// TODO
}
void _rebuild() {
setState(() {
});
}
Future<String> _getToken() async{
return await SharedPreferences.getInstance()
.then((SharedPreferences sp)=> sp.getString(TOKEN)
);
}
}}
答案 0 :(得分:1)
切换选项卡时使页面保持活动状态的解决方案是将页面包装在 IndexedStack 中。
class Tabbar extends StatefulWidget {
Tabbar({this.screens});
static const Tag = "Tabbar";
final List<Widget> screens;
@override
State<StatefulWidget> createState() {
return _TabbarState();
}
}
class _TabbarState extends State<Tabbar> {
int _currentIndex = 0;
Widget currentScreen;
@override
Widget build(BuildContext context) {
var _l10n = PackedLocalizations.of(context);
return Scaffold(
body: IndexedStack(
index: _currentIndex,
children: widget.screens,
),
bottomNavigationBar: BottomNavigationBar(
fixedColor: Colors.black,
type: BottomNavigationBarType.fixed,
onTap: onTabTapped,
currentIndex: _currentIndex,
items: [
BottomNavigationBarItem(
icon: new Icon(Icons.format_list_bulleted),
title: new Text(_l10n.tripsTitle),
),
BottomNavigationBarItem(
icon: new Icon(Icons.settings),
title: new Text(_l10n.settingsTitle),
)
],
),
);
}
void onTabTapped(int index) {
setState(() {
_currentIndex = index;
});
}
}
答案 1 :(得分:0)
我绝对建议您观看 @amrnt 视频。但是对于那些想要直接答案的人,您需要为底部小节的每一页实例化一个PageStorageKey,然后使每一页通过构造函数接收其PageStorageKey。
答案 2 :(得分:0)
更好的方法是使用IndexedStack而不是PageStorage或AutomaticKeepAliveClientMixin。
[4, -9, -1, 9, -1, -3, 8, 8, 0, -9, -8, 7, 6, 5, -6, 5, -4, 2, 1, -1, -6, 0, 3, -7, 9, 9, 6, -5, -8, 1, -8, -1, -1]
IndexedStack Widget是Stack Widget的子类 它显示了所提供的“孩子”列表中的一个孩子。它的大小和最大的孩子一样大。它会保留所有孩子的状态。