Related
these my two classes(two pages). these two classes open multiple times.
I put debug point in futurebuilder in two classes.
debug point running,
MainCategory page and got to the next page
SubCategory page and again running MainCategory page(previous page) futurebuilder and again running MainCategory page futurebuilder
navigate subcategory page to third page running subcategory page and main category page
I upload my two classes to GitHub and please let me know what the issue is.
MainCategory code: https://github.com/bhanuka96/ios_login/blob/master/MainCategory.dart
SubCategory code: https://github.com/bhanuka96/ios_login/blob/master/subCategory.dart
As stated in the documentation, you should not fetch the Future for the Futurebuilder during the widget's build event.
https://docs.flutter.io/flutter/widgets/FutureBuilder-class.html
The future must have been obtained earlier, e.g. during
State.initState, State.didUpdateConfig, or
State.didChangeDependencies. It must not be created during the
State.build or StatelessWidget.build method call when constructing the
FutureBuilder. If the future is created at the same time as the
FutureBuilder, then every time the FutureBuilder's parent is rebuilt,
the asynchronous task will be restarted.
So, try to move your call to getRegister method outside the build method and replace it with the returned Future value.
For example, below I have a class that returns a Future value which will be consumed with the help of FutureBuilder.
class MyApiHelper{
static Future<List<String>> getMyList() async {
// your implementation to make server calls
return List<String>();
}
}
Now, inside your widget, you will have something like this:
class _MyHomePageState extends State<MyHomePage> {
Future<List<String>> _myList;
#override
void initState() {
super.initState();
_myList = MyApiHelper.getMyList();
}
#override
Widget build(BuildContext context) {
return Scaffold(body: FutureBuilder(
future: _myList,
builder: (_, AsyncSnapshot<List<String>> snapLs) {
if(!snapLs.hasData) return CircularProgressIndicator();
return ListView.builder(
itemCount: snapLs.data.length,
itemBuilder: (_, index) {
//show your list item row here...
},
);
},
));
}
}
As shown above, the Future is fetched in the initState function and used inside the build method and used by FutureBuilder.
I hope this was helpful.
Thanks.
If you happen to use Provider, here's (in my opinion) a clearer alternative based on your question:
class MyHomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return FutureProvider<List<String>>(
create: (_) => MyApiHelper.getMyList(),
child: Consumer<List<String>>(
builder: (_, list, __) {
if (list == null) return CircularProgressIndicator();
return ListView.builder(
itemCount: list.length,
itemBuilder: (_, index) {
//show your list item row here...
},
);
};
),
);
}
}
This can also be achieved of course as a StatefulWidget as suggested by the other answer, or even with flutter_hooks as explained in Why is my Future/Async Called Multiple Times?
You can create new Widget and pass Function to
returnFuture as
() {
return YourFuture;
}
import 'dart:developer';
import 'package:flutter/material.dart';
class MyFutureBuilder<T> extends StatefulWidget {
final Future<T> Function() returnFuture;
final AsyncWidgetBuilder<T> builder;
final T initialData;
MyFutureBuilder({
this.returnFuture,
#required this.builder,
this.initialData,
Key key,
}) : super(key: key);
#override
_MyFutureBuilderState<T> createState() => _MyFutureBuilderState<T>();
}
class _MyFutureBuilderState<T> extends State<MyFutureBuilder<T>> {
bool isLoading = false;
Future<T> future;
#override
void initState() {
super.initState();
future = widget.returnFuture();
}
#override
Widget build(BuildContext context) {
return FutureBuilder(
builder: widget.builder,
initialData: widget.initialData,
future: future,
);
}
}
Example
MyFutureBuilder<List<User>>(
returnFuture: () {
return moderatorUserProvider
.getExecutorsAsModeratorByIds(val.users,
save: true);
},
builder: (cont, asyncData) {
if (asyncData.connectionState !=
ConnectionState.done) {
return Center(
child: MyCircularProgressIndicator(
color: ModeratorColor.executors.color,
),
);
}
return Column(
children: asyncData.data
.map(
(singlExecutor) =>
ChooseInfoButton(
title:
'${singlExecutor.firstName} ${singlExecutor.secondName}',
subTitle: 'Business analyst',
middleText: '4.000 NOK',
subMiddleText: 'full time',
label: 'test period',
subLabel: '1.5 month',
imageUrl:
assetsUrl + 'download.jpeg',
onTap: () {
Navigator.of(context).push(
MaterialPageRoute(
builder: (_) =>
ModeratorExecutorEditPage(),
),
);
},
),
)
.toList());
},
)
```
I have a listview.builder inside a stateful widget and i made a separate stateful widget for the item (ImageCard).
inside the ImageCard widget i have a like button when i click it its color change to red(like), gray(dislike).
the problem is that when i scroll down and return back the color is always gray which means that no state is saved!
how can i notify the parent stateful widget to keep the state?
Parent stateful widget
#override
Widget build(BuildContext context) {
return _buildListView(models, _scrollController);
}
Widget _buildListView(
List<PhotoModel> models, ScrollController scrollController) {
return Container(
child: ListView.builder(
controller: scrollController,
itemCount: models.length,
itemBuilder: (context, int index) {
if (index == models.length - 1) {
return SpinKitThreeBounce(
color: Colors.purple,
size: 30.0,
);
} else {
return ImageCard(
models[index].regularPhotoUrl,
models[index].mediumProfilePhotoUrl,
models[index].name,
models[index].color);
}
}));
}
child stateful widget
class ImageCard extends StatefulWidget {
final String imageUrl, userProfilePic, userName, color;
ImageCard(this.imageUrl, this.userProfilePic, this.userName, this.color);
#override
_ImageCardState createState() => _ImageCardState();
}
class _ImageCardState extends State<ImageCard> {
bool isLiked = false, isFollowing = false;
#override
Widget build(BuildContext context) {
return new Card( ....
void _onLikedBtnClicked() {
setState(() {
if (isLiked)
isLiked = false;
else {
isLiked = true;
}
});
}
Flutter will automatically disposes the widget that moves out of screen, and when they re-appear, they will be re-built rather than recovered.
So common practice is to save the state in a high-level widget, which contains at least a complete aspect of business logic and is not going to be disposed anytime soon. Then a change in the state is mapped into child widgets.
For your specific case, a simple solution is: you store the information in the parent widget, and maps them to a ImageCard inside the parent widget's build function.
Add isliked,isfollowing property to the model, then
class SomeParentState extends State<SomeParent> {
List<Model> models;
//.......
#override
Widget build(BuildContext context) {
return _buildListView(models, _scrollController);
}
Widget _buildListView(List<PhotoModel> models,
ScrollController scrollController) {
return Container(
child: ListView.builder(
controller: scrollController,
itemCount: models.length,
itemBuilder: (context, int index) {
if (index == models.length - 1) {
return SpinKitThreeBounce(
color: Colors.purple,
size: 30.0,
);
} else {
return ImageCard(
models[index].regularPhotoUrl,
models[index].mediumProfilePhotoUrl,
models[index].name,
models[index].color,
models[index].isLiked,
models[index].isFollowing,
() {
setState(() {
models[index].isLiked = !models[index].isLiked;
});
},
() {
setState(() {
models[index].isFollowing = !models[index].isFollowing;
});
},
);
}
}));
}
}
class ImageCard extends StatelessWidget{
ImageCard(
//...,
this.isLiked,
this.isFollowing,
this.likeBtnClickedListener,
this.followBtnClickedListener,
)
//...
Widget build(BuildContext context){
return Card(
//.......
IconButton(
onPressed: likeBtnClickedListener,
),
IconButton(
onPressed: followBtnClickedListener,
),
)
}
}
This should basically solve your problem. Anyway, it is easier to access and sync the data in the child widgets in this method.
If you find it easier to just keep the child widget alive, you can read the documentation of AutomaticKeepAliveClientMixin. It will stop flutter from killing this widget when it moves out of sight. But it is risky of causing memory leak.
To maintain the state of a widget inside a ListView, you need to AutomaticKeepAlive or AutomaticKeepAliveMixin (for custom widgets)
This will ensure the State instance is not destroyed when leaving the screen
ListView(
children: [
// Not kept alive
Text('Hello World'),
// kept alive
AutomaticKeepAlive(
child: Text("Hello World"),
),
]
),
You should keep your state separately then. You could make a List<bool> and have one value in there for each of the List items. You probably want to save or use the data at some point anyways, then this mechanism is going to be useless.
I want to update my ListView if i remove or add items. Right now i just want to delete items and see the deletion of the items immediately.
My application is more complex so i wrote a small example project to show my problems.
The TestItem class holds some data entries:
class TestItem {
static int id = 1;
bool isFinished = false;
String text;
TestItem() {
text = "Item ${id++}";
}
}
The ItemInfoViewWidget is the UI representation of the TestItem and removes the item if it is finished (whenever the Checkbox is changed to true).
class ItemInfoViewWidget extends StatefulWidget {
TestItem item;
List<TestItem> items;
ItemInfoViewWidget(this.items, this.item);
#override
_ItemInfoViewWidgetState createState() =>
_ItemInfoViewWidgetState(this.items, this.item);
}
class _ItemInfoViewWidgetState extends State<ItemInfoViewWidget> {
TestItem item;
List<TestItem> items;
_ItemInfoViewWidgetState(this.items, this.item);
#override
Widget build(BuildContext context) {
return new Card(
child: new Column(
children: <Widget>[
new Text(this.item.text),
new Checkbox(
value: this.item.isFinished, onChanged: isFinishedChanged)
],
),
);
}
void isFinishedChanged(bool value) {
setState(() {
this.item.isFinished = value;
this.items.remove(this.item);
});
}
}
The ItemViewWidget class builds the ListView.
class ItemViewWidget extends StatefulWidget {
List<TestItem> items;
ItemViewWidget(this.items);
#override
_ItemViewWidgetState createState() => _ItemViewWidgetState(this.items);
}
class _ItemViewWidgetState extends State<ItemViewWidget> {
List<TestItem> items;
_ItemViewWidgetState(this.items);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: new Text('Test'),
),
body: ListView.builder(
itemCount: this.items.length,
itemBuilder: (BuildContext context, int index) {
return new ItemInfoViewWidget(this.items, this.items[index]);
}),
);
}
}
The MyApp shows one TestItem and a button that navigates to the ItemViewWidget page.
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(
primarySwatch: Colors.blue,
),
home: new MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
List<TestItem> items = new List<TestItem>();
_MyHomePageState() {
for (int i = 0; i < 20; i++) {
this.items.add(new TestItem());
}
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text(widget.title),
),
body: new Column(
children: <Widget>[
ItemInfoViewWidget(this.items, this.items.first),
FlatButton(
child: new Text('Open Detailed View'),
onPressed: buttonClicked,
)
],
));
}
void buttonClicked() {
Navigator.push(
context,
MaterialPageRoute(builder: (context) => ItemViewWidget(this.items)),
);
}
}
If i toggle the Checkbox of the first item, the Checkbox is marked as finished (as expected), but it is not removed from the UI - however it is removed from the list.
Then I go back to the Main page and I can observe that Item 1 is checked there as well.
So if I go to the ItemViewWidget page again, I can observe that the checked items are no longer present.
Based on these observations, I come to the conclusion that my implementation works, but my UI is not updating.
How can I change my code to make an immediate update of the UI possible?
Edit: This is not a duplicate, because
I dont want to create a new instance of my list just to get the UI updated.
The answer does not work: I added this.items = List.from(this.items); but the behavior of my app is the same as already described above.
I don't want to break my reference chain by calling List.from, because my architecture has one list that is referenced by several classes. If i break the chain i have to update all references by my own. Is there a problem with my architecture?
I dont want to create a new instance of my list just to get the UI updated.
Flutter uses immutable object. Not following this rule is going against the reactive framework. It is a voluntary requirement to reduce bugs.
Fact is, this immutability is here especially to prevents developers from doing what you currently do: Having a program that depends on sharing the same instance of an object between classes; as multiple classes may want to modify it.
The real problem lies in the fact that it is your list item that removes delete an element from your list.
The thing is since it's your item which does the computing, the parent is never notified that the list changed. Therefore it doesn't know it should rerender. So nothing visually change.
To fix that you should move the deletion logic to the parent. And make sure that the parent correctly calls setState accordingly. This would translate into passing a callback to your list item, which will be called on deletion.
Here's an example:
class MyList extends StatefulWidget {
#override
_MyListState createState() => _MyListState();
}
class _MyListState extends State<MyList> {
List<String> list = List.generate(100, (i) => i.toString());
#override
Widget build(BuildContext context) {
return ListView.builder(
itemCount: list.length,
itemBuilder: (context, index) {
return MyItem(list[index], onDelete: () => removeItem(index));
},
);
}
void removeItem(int index) {
setState(() {
list = List.from(list)
..removeAt(index);
});
}
}
class MyItem extends StatelessWidget {
final String title;
final VoidCallback onDelete;
MyItem(this.title, {this.onDelete});
#override
Widget build(BuildContext context) {
return ListTile(
title: Text(this.title),
onTap: this.onDelete,
);
}
}
I'm currently working on building a Flutter app that will preserve states when navigating from one screen, to another, and back again when utilizing BottomNavigationBar. Just like it works in the Spotify mobile application; if you have navigated down to a certain level in the navigation hierarchy on one of the main screens, changing screen via the bottom navigation bar, and later changing back to the old screen, will preserve where the user were in that hierarchy, including preservation of the state.
I have run my head against the wall, trying various different things without success.
I want to know how I can prevent the pages in pageChooser(), when toggled once the user taps the BottomNavigationBar item, from rebuilding themselves, and instead preserve the state they already found themselves in (the pages are all stateful Widgets).
import 'package:flutter/material.dart';
import './page_plan.dart';
import './page_profile.dart';
import './page_startup_namer.dart';
void main() => runApp(new Recipher());
class Recipher extends StatelessWidget {
#override
Widget build(BuildContext context) {
return new Pages();
}
}
class Pages extends StatefulWidget {
#override
createState() => new PagesState();
}
class PagesState extends State<Pages> {
int pageIndex = 0;
pageChooser() {
switch (this.pageIndex) {
case 0:
return new ProfilePage();
break;
case 1:
return new PlanPage();
break;
case 2:
return new StartUpNamerPage();
break;
default:
return new Container(
child: new Center(
child: new Text(
'No page found by page chooser.',
style: new TextStyle(fontSize: 30.0)
)
),
);
}
}
#override
Widget build(BuildContext context) {
return new MaterialApp(
home: new Scaffold(
body: pageChooser(),
bottomNavigationBar: new BottomNavigationBar(
currentIndex: pageIndex,
onTap: (int tappedIndex) { //Toggle pageChooser and rebuild state with the index that was tapped in bottom navbar
setState(
(){ this.pageIndex = tappedIndex; }
);
},
items: <BottomNavigationBarItem>[
new BottomNavigationBarItem(
title: new Text('Profile'),
icon: new Icon(Icons.account_box)
),
new BottomNavigationBarItem(
title: new Text('Plan'),
icon: new Icon(Icons.calendar_today)
),
new BottomNavigationBarItem(
title: new Text('Startup'),
icon: new Icon(Icons.alarm_on)
)
],
)
)
);
}
}
For keeping state in BottomNavigationBar, you can use IndexedStack
#override
Widget build(BuildContext context) {
return Scaffold(
bottomNavigationBar: BottomNavigationBar(
onTap: (index) {
setState(() {
current_tab = index;
});
},
currentIndex: current_tab,
items: [
BottomNavigationBarItem(
...
),
BottomNavigationBarItem(
...
),
],
),
body: IndexedStack(
children: <Widget>[
PageOne(),
PageTwo(),
],
index: current_tab,
),
);
}
Late to the party, but I've got a simple solution. Use the PageView widget with the AutomaticKeepAliveClinetMixin.
The beauty of it that it doesn't load any tab until you click on it.
The page that includes the BottomNavigationBar:
var _selectedPageIndex;
List<Widget> _pages;
PageController _pageController;
#override
void initState() {
super.initState();
_selectedPageIndex = 0;
_pages = [
//The individual tabs.
];
_pageController = PageController(initialPage: _selectedPageIndex);
}
#override
void dispose() {
_pageController.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
...
body: PageView(
controller: _pageController,
physics: NeverScrollableScrollPhysics(),
children: _pages,
),
bottomNavigationBar: BottomNavigationBar(
...
currentIndex: _selectedPageIndex,
onTap: (selectedPageIndex) {
setState(() {
_selectedPageIndex = selectedPageIndex;
_pageController.jumpToPage(selectedPageIndex);
});
},
...
}
The individual tab:
class _HomeState extends State<Home> with AutomaticKeepAliveClientMixin<Home> {
#override
bool get wantKeepAlive => true;
#override
Widget build(BuildContext context) {
//Notice the super-call here.
super.build(context);
...
}
}
I've made a video about it here.
Use AutomaticKeepAliveClientMixin to force your tab content to not be disposed.
class PersistantTab extends StatefulWidget {
#override
_PersistantTabState createState() => _PersistantTabState();
}
class _PersistantTabState extends State<PersistantTab> with AutomaticKeepAliveClientMixin {
#override
Widget build(BuildContext context) {
return Container();
}
// Setting to true will force the tab to never be disposed. This could be dangerous.
#override
bool get wantKeepAlive => true;
}
To make sure your tab does get disposed when it doesn't require to be persisted, make wantKeepAlive return a class variable. You must call updateKeepAlive() to update the keep alive status.
Example with dynamic keep alive:
// class PersistantTab extends StatefulWidget ...
class _PersistantTabState extends State<PersistantTab>
with AutomaticKeepAliveClientMixin {
bool keepAlive = false;
#override
void initState() {
doAsyncStuff();
}
Future doAsyncStuff() async {
keepAlive = true;
updateKeepAlive();
// Keeping alive...
await Future.delayed(Duration(seconds: 10));
keepAlive = false;
updateKeepAlive();
// Can be disposed whenever now.
}
#override
bool get wantKeepAlive => keepAlive;
#override
Widget build(BuildContext context) {
super.build();
return Container();
}
}
Instead of returning new instance every time you run pageChooser, have one instance created and return the same.
Example:
class Pages extends StatefulWidget {
#override
createState() => new PagesState();
}
class PagesState extends State<Pages> {
int pageIndex = 0;
// Create all the pages once and return same instance when required
final ProfilePage _profilePage = new ProfilePage();
final PlanPage _planPage = new PlanPage();
final StartUpNamerPage _startUpNamerPage = new StartUpNamerPage();
Widget pageChooser() {
switch (this.pageIndex) {
case 0:
return _profilePage;
break;
case 1:
return _planPage;
break;
case 2:
return _startUpNamerPage;
break;
default:
return new Container(
child: new Center(
child: new Text(
'No page found by page chooser.',
style: new TextStyle(fontSize: 30.0)
)
),
);
}
}
#override
Widget build(BuildContext context) {
return new MaterialApp(
home: new Scaffold(
body: pageChooser(),
bottomNavigationBar: new BottomNavigationBar(
currentIndex: pageIndex,
onTap: (int tappedIndex) { //Toggle pageChooser and rebuild state with the index that was tapped in bottom navbar
setState(
(){ this.pageIndex = tappedIndex; }
);
},
items: <BottomNavigationBarItem>[
new BottomNavigationBarItem(
title: new Text('Profile'),
icon: new Icon(Icons.account_box)
),
new BottomNavigationBarItem(
title: new Text('Plan'),
icon: new Icon(Icons.calendar_today)
),
new BottomNavigationBarItem(
title: new Text('Startup'),
icon: new Icon(Icons.alarm_on)
)
],
)
)
);
}
}
Or you can make use of widgets like PageView or Stack to achieve the same.
Hope that helps!
Use “IndexedStack Widget” with “Bottom Navigation Bar Widget” to keep state of Screens/pages/Widget
Provide list of Widget to IndexedStack and index of widget you want to show because IndexedStack show single widget from list at one time.
final List<Widget> _children = [
FirstClass(),
SecondClass()
];
Scaffold(
body: IndexedStack(
index: _selectedPage,
children: _children,
),
bottomNavigationBar: BottomNavigationBar(
........
........
),
);
The most convenient way I have found to do so is using PageStorage widget along with PageStorageBucket, which acts as a key value persistent layer.
Go through this article for a beautiful explanation -> https://steemit.com/utopian-io/#tensor/persisting-user-interface-state-and-building-bottom-navigation-bars-in-dart-s-flutter-framework
Do not use IndexStack Widget, because it will instantiate all the tabs together, and suppose if all the tabs are making a network request then the callbacks will be messed up the last API calling tab will probably have the control of the callback.
Use AutomaticKeepAliveClientMixin for your stateful widget it is the simplest way to achieve it without instantiating all the tabs together.
My code had interfaces that were providing the respective responses to the calling tab I implemented it the following way.
Create your stateful widget
class FollowUpsScreen extends StatefulWidget {
FollowUpsScreen();
#override
State<StatefulWidget> createState() {
return FollowUpsScreenState();
}
}
class FollowUpsScreenState extends State<FollowUpsScreen>
with AutomaticKeepAliveClientMixin<FollowUpsScreen>
implements OperationalControls {
#override
Widget build(BuildContext context) {
//do not miss this line
super.build(context);
return .....;
}
#override
bool get wantKeepAlive => true;
}
This solution is based on CupertinoTabScaffold's implementation which won't load screens unnecessary.
import 'package:flutter/material.dart';
enum MainPage { home, profile }
class BottomNavScreen extends StatefulWidget {
const BottomNavScreen({super.key});
#override
State<BottomNavScreen> createState() => _BottomNavScreenState();
}
class _BottomNavScreenState extends State<BottomNavScreen> {
var currentPage = MainPage.home;
#override
Widget build(BuildContext context) {
return Scaffold(
body: PageSwitchingView(
currentPageIndex: MainPage.values.indexOf(currentPage),
pageCount: MainPage.values.length,
pageBuilder: _pageBuilder,
),
bottomNavigationBar: BottomNavigationBar(
currentIndex: MainPage.values.indexOf(currentPage),
onTap: (index) => setState(() => currentPage = MainPage.values[index]),
items: const [
BottomNavigationBarItem(
label: 'Home',
icon: Icon(Icons.home),
),
BottomNavigationBarItem(
label: 'Profile',
icon: Icon(Icons.account_circle),
),
],
),
);
}
Widget _pageBuilder(BuildContext context, int index) {
final page = MainPage.values[index];
switch (page) {
case MainPage.home:
return ...
case MainPage.profile:
return ...
}
}
}
/// A widget laying out multiple pages with only one active page being built
/// at a time and on stage. Off stage pages' animations are stopped.
class PageSwitchingView extends StatefulWidget {
const PageSwitchingView({
super.key,
required this.currentPageIndex,
required this.pageCount,
required this.pageBuilder,
});
final int currentPageIndex;
final int pageCount;
final IndexedWidgetBuilder pageBuilder;
#override
State<PageSwitchingView> createState() => _PageSwitchingViewState();
}
class _PageSwitchingViewState extends State<PageSwitchingView> {
final List<bool> shouldBuildPage = <bool>[];
#override
void initState() {
super.initState();
shouldBuildPage.addAll(List<bool>.filled(widget.pageCount, false));
}
#override
void didUpdateWidget(PageSwitchingView oldWidget) {
super.didUpdateWidget(oldWidget);
// Only partially invalidate the pages cache to avoid breaking the current
// behavior. We assume that the only possible change is either:
// - new pages are appended to the page list, or
// - some trailing pages are removed.
// If the above assumption is not true, some pages may lose their state.
final lengthDiff = widget.pageCount - shouldBuildPage.length;
if (lengthDiff > 0) {
shouldBuildPage.addAll(List<bool>.filled(lengthDiff, false));
} else if (lengthDiff < 0) {
shouldBuildPage.removeRange(widget.pageCount, shouldBuildPage.length);
}
}
#override
Widget build(BuildContext context) {
return Stack(
fit: StackFit.expand,
children: List<Widget>.generate(widget.pageCount, (int index) {
final active = index == widget.currentPageIndex;
shouldBuildPage[index] = active || shouldBuildPage[index];
return HeroMode(
enabled: active,
child: Offstage(
offstage: !active,
child: TickerMode(
enabled: active,
child: Builder(
builder: (BuildContext context) {
return shouldBuildPage[index] ? widget.pageBuilder(context, index) : Container();
},
),
),
),
);
}),
);
}
}
proper way of preserving tabs state in bottom nav bar is by wrapping the whole tree with PageStorage() widget which takes a PageStorageBucket bucket as a required named parameter and for those tabs to which you want to preserve its state pas those respected widgets with PageStorageKey(<str_key>) then you are done !! you can see more details in this ans which i've answered few weeks back on one question : https://stackoverflow.com/a/68620032/11974847
there's other alternatives like IndexedWidget() but you should beware while using it , i've explained y we should be catious while using IndexedWidget() in the given link answer
good luck mate ..
Is there a way to force Flutter to redraw all widgets (e.g. after locale change)?
Your Widget should have a setState() method, everytime this method is called, the widget is redrawn.
Documentation : Widget setState()
Old question, but here is the solution:
In your build method, call the rebuildAllChildren function and pass it the context:
#override
Widget build(BuildContext context) {
rebuildAllChildren(context);
return ...
}
void rebuildAllChildren(BuildContext context) {
void rebuild(Element el) {
el.markNeedsBuild();
el.visitChildren(rebuild);
}
(context as Element).visitChildren(rebuild);
}
This will visit all children and mark them as needing to rebuild.
If you put this code in the topmost widget in your widgets tree, it will rebuild everything.
Also note you must order that specific widget to rebuild. Also you could have some boolean so that the rebuild of that widget only rebuilds all of its children when you really need it (it's an expensive operation, of course).
IMPORTANT: This is a hack, and you should only do this if you know what you are doing, and have strong reason to do so. One example where this is necessary is in my internationalization package: i18_extension. As Collin Jackson explained in his answer, you are really not supposed to do this in general.
This type of use case, where you have data that children can read but you don't want to explicitly pass the data to the constructor arguments of all your children, usually calls for an InheritedWidget. Flutter will automatically track which widgets depend on the data and rebuild the parts of your tree that have changed. There is a LocaleQuery widget that is designed to handle locale changes, and you can see how it's used in the Stocks example app.
Briefly, here's what Stocks is doing:
Put a callback on root widget (in this case, StocksApp) for handling locale changes. This callback does some work and then returns a customized instance of LocaleQueryData
Register this callback as the onLocaleChanged argument to the MaterialApp constructor
Child widgets that need locale information use LocaleQuery.of(context).
When the locale changes, Flutter only redraws widgets that have dependencies on the locale data.
If you want to track something other than locale changes, you can make your own class that extends InheritedWidget, and include it in the hierarchy near the root of your app. Its parent should be a StatefulWidget with key set to a GlobalKey that accessible to the children. The State of the StatefulWidget should own the data you want to distribute and expose methods for changing it that call setState. If child widgets want change the State's data, they can use the global key to get a pointer to the State (key.currentState) and call methods on it. If they want to read the data, they can call the static of(context) method of your subclass of InheritedWidget and that will tell Flutter that these widgets need to rebuilt whenever your State calls setState.
Refreshing the whole widget tree might be expensive and when you do it in front of the users eyes that wouldn't seem sweet.
so for this purpose flutter has ValueListenableBuilder<T> class. It allows you to rebuild only some of the widgets necessary for your purpose and skip the expensive widgets.
you can see the documents here ValueListenableBuilder flutter docs
or just the sample code below:
return Scaffold(
appBar: AppBar(
title: Text(widget.title)
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text('You have pushed the button this many times:'),
ValueListenableBuilder(
builder: (BuildContext context, int value, Widget child) {
// This builder will only get called when the _counter
// is updated.
return Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
Text('$value'),
child,
],
);
},
valueListenable: _counter,
// The child parameter is most helpful if the child is
// expensive to build and does not depend on the value from
// the notifier.
child: goodJob,
)
],
),
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.plus_one),
onPressed: () => _counter.value += 1,
),
);
And also never forget the power of setState(() {});
I explain how to create a custom 'AppBuilder' widget in this post.
https://hillelcoren.com/2018/08/15/flutter-how-to-rebuild-the-entire-app-to-change-the-theme-or-locale/
You can use the widget by wrapping your MaterialApp with it, for example:
Widget build(BuildContext context) {
return AppBuilder(builder: (context) {
return MaterialApp(
...
);
});
}
You can tell the app to rebuild using:
AppBuilder.of(context).rebuild();
Simply Use:
Navigator.popAndPushNamed(context,'/screenname');
Whenever you need to refresh :)
What might work for your use case is using the Navigator to reload the page. I do this when switching between "real" and "demo" mode in my app. Here's an example :
Navigator.of(context).push(
new MaterialPageRoute(
builder: (BuildContext context){
return new SplashPage();
}
)
);
You can replace "new SplashPage()" in the above code with whatever main widget (or screen) you would like to reload. This code can be called from anywhere you have access to a BuildContext (which is most places in the UI).
Just use a Key on one of your high-level widgets, everything below this will lose state:
Key _refreshKey = UniqueKey();
void _handleLocalChanged() => setState((){
_refreshKey = UniqueKey()
});
Widget build(BuildContext context){
return MaterialApp(
key: _refreshKey ,
...
)
}
You could also use a value key like:
return MaterialApp(
key: ValueKey(locale.name)
...
);
Why not just have Flutter.redrawAllWidgetsBecauseISaidSo();? –
TimSim
There kinda is:
Change to key to redraw statefull child widgets.
Jelena Lecic explained it good enough for me on medium.
import 'package:flutter/material.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key? key}) : super(key: key);
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
var _forceRedraw; // generate the key from this
void _incrementCounter() {
setState(() {
_counter++;
_forceRedraw = Object();
});
}
#override
void initState() {
_forceRedraw = Object();
super.initState();
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
MyStatefullTextWidget(
key: ValueKey(_forceRedraw),
counter: _counter,
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}
class MyStatefullTextWidget extends StatefulWidget {
final int counter;
const MyStatefullTextWidget({
required this.counter,
Key? key,
}) : super(key: key);
#override
_MyStatefullTextWidgetState createState() => _MyStatefullTextWidgetState();
}
class _MyStatefullTextWidgetState extends State<MyStatefullTextWidget> {
#override
Widget build(BuildContext context) {
return Text(
'You have pushed the button this many times:${widget.counter}',
);
}
}
Simply Use:
Navigator.popAndPushNamed(context,'/xxx');
I my case it was enough to reconstruct the item.
Changed:
return child;
}).toList(),
To:
return SetupItemTypeButton(
type: child.type,
icon: child.icon,
active: _selected[i] == true,
onTap: ...,
);
}).toList(),
class SetupItemTypeButton extends StatelessWidget {
final dynamic type;
final String icon;
estureTapCallback onTap;
SetupItemTypeButton({Key? key, required this.type, required this.icon, required this.onTap}) : super(key: key);
#override
Widget build(BuildContext context) {
return Container();
}
}
class SetupItemsGroup extends StatefulWidget {
final List<SetupItemTypeButton> children;
final Function(int index)? onSelect;
SetupItemsGroup({required this.children, this.onSelect});
#override
State<SetupItemsGroup> createState() => _SetupItemsGroupState();
}
class _SetupItemsGroupState extends State<SetupItemsGroup> {
final Map<int, bool> _selected = {};
#override
Widget build(BuildContext context) {
int index = 0;
return Container(
child: GridView.count(
children: widget.children.map((child) {
return SetupItemTypeButton(
type: child.type,
icon: child.icon,
active: _selected[i] == true,
onTap: () {
if (widget.onSelect != null) {
int i = index++;
child.active = _selected[i] == true;
setState(() {
_selected[i] = _selected[i] != true;
child.onTap();
widget.onSelect!(i);
});
}
},
);
}).toList(),
),
);
}
}