Problem: I click the button 'do something' and the image can't seem to change from 'hello' to 'goodbye'. The error coming back is
'Error: The argument type 'Image' can't be assigned to the parameter type 'String'.
'Image' is from 'package:flutter/src/widgets/image.dart' ('../../Development/flutter/packages/flutter/lib/src/widgets/image.dart').
return Image.asset(myValue);'
Is it possible to change the String into an image so it will read the image and display it on the screen?
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Provider<MyModel>(// <--- Provider
create: (context) => MyModel(),
child: Consumer<MyModel>( // <--- MyModel Consumer
builder: (context, myModel, child) {
return ValueListenableProvider<Image>.value( // <--- ValueListenableProvider
value: myModel.someValue,
child: MaterialApp(
home: Scaffold(
appBar: AppBar(title: Text('My App')),
body: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Flexible(
child: Container(
padding: const EdgeInsets.all(20),
color: Colors.green[200],
child: Consumer<MyModel>( // <--- Consumer
builder: (context, myModel, child) {
return RaisedButton(
child: Text('Do something'),
onPressed: (){
myModel.doSomething();
},
);
},
)
),
),
Flexible(
child: Container(
padding: const EdgeInsets.all(35),
color: Colors.blue[200],
child: Consumer<Image>(// <--- String Consumer
builder: (context, myValue, child) {
return Image.asset(myValue);
},
),
),
),
],
),
),
),
);
}),
);
}
}
class MyModel { // <--- MyModel
ValueNotifier<Image> someValue = ValueNotifier(Image.asset('images/hello.png')); // <--- ValueNotifier
void doSomething() {
someValue.value = Image.asset('images/goodbye.png');
print(someValue.value);
}
}
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Provider<MyModel>(
// <--- Provider
create: (context) => MyModel(),
child:
Consumer<MyModel>(// <--- MyModel Consumer
builder: (context, myModel, child) {
return ValueListenableProvider<Image>.value(
// <--- ValueListenableProvider
value: myModel.someValue,
child: MaterialApp(
home: Scaffold(
appBar: AppBar(title: Text('My App')),
body: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Flexible(
child: Container(
padding: const EdgeInsets.all(20),
color: Colors.green[200],
child: Consumer<MyModel>(
// <--- Consumer
builder: (context, myModel, child) {
return RaisedButton(
child: Text('Do something'),
onPressed: () {
myModel.doSomething();
},
);
},
)),
),
Flexible(
child: Container(
padding: const EdgeInsets.all(35),
color: Colors.blue[200],
child: Consumer<Image>(
// <--- String Consumer
builder: (context, myValue, child) {
return myValue; // <--- **Change**
},
),
),
),
],
),
),
),
);
}),
);
}
}
class MyModel {
// <--- MyModel
ValueNotifier<Image> someValue =
ValueNotifier(Image.asset('images/hello.png')); // <--- ValueNotifier
void doSomething() { // <--- **Change**
if (someValue.value.toString() ==
Image.asset('images/hello.png').toString()) {
someValue.value = Image.asset('images/goodbye.png');
} else if (someValue.value.toString() ==
Image.asset('images/goodbye.png').toString()) {
someValue.value = Image.asset('images/hello.png');
}
}
}
myValue is already an image so you don't need to open it again from Image.asset also added feature to change image back and forth for your doSomething() function
I tried to wrap it in a Hero widget, as that should achieve what I want. This works with BottomNavigationBar, but not with BottomAppBar, which gives this error: Scaffold.geometryOf() called with a context that does not contain a Scaffold. I tried to give it a context by using Builder, but that did not work either. Here is a sample app to showcase the behaviour:
void main() {
runApp(
MaterialApp(
home: PageOne(),
),
);
}
Widget _bottomNavigationBar() {
return BottomNavigationBar(items: [
BottomNavigationBarItem(icon: Icon(Icons.menu), title: Text('menu')),
BottomNavigationBarItem(icon: Icon(Icons.arrow_back), title: Text('back')),
]);
}
Widget _bottomAppBar() {
return BottomAppBar(
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
IconButton(icon: Icon(Icons.menu), onPressed: null),
IconButton(icon: Icon(Icons.arrow_back), onPressed: null),
],
),
);
}
class PageOne extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
bottomNavigationBar: Hero(
tag: 'bottomNavigationBar',
child: _bottomAppBar(),
),
body: Center(
child: IconButton(
iconSize: 200,
icon: Icon(Icons.looks_two),
onPressed: () => Navigator.push(
context,
MaterialPageRoute(builder: (context) => PageTwo()),
),
),
),
);
}
}
class PageTwo extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
bottomNavigationBar: Hero(
tag: 'bottomNavigationBar',
child: _bottomAppBar(),
),
body: Center(
child: IconButton(
iconSize: 200,
icon: Icon(Icons.looks_one),
onPressed: () => Navigator.pop(context),
),
),
);
}
}
The problem seems to be the animation that is used with the Navigation stack. Therefore, getting rid of the animation during the page load will stop this animation. I added the PageRouteBuilder to the PageOne class in your example to get rid of the Navigation stack animation. Use the code below to replace the PageOne class from your example.
class PageOne extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
bottomNavigationBar: _bottomAppBar(),
body: Center(
child: IconButton(
iconSize: 200,
icon: Icon(Icons.looks_two),
onPressed: () => Navigator.push(
context,
PageRouteBuilder(
pageBuilder: (context, anim1, anim2) => PageTwo(),
transitionsBuilder: (context, anim1, anim2, child) =>
Container(child: child),
),
),
),
),
);
}
}
There are additional ways to control the animation for Navigation here
(Oh, and I got rid of the Hero() widget)
I have solved this by wrapping the Row with a Hero widget in BottomAppBar. This still allows page transitions, and does not animate the BottomAppBar as intended.
BottomAppBar(
child: Hero(
tag: 'bottomAppBar',
child: Material(
child: Row(
...
),
),
),
);
However, this has laggy animations when using a CircularNotchedRectangle.
i have a screen that build using MaterialApp, DefaultTabController, Scaffold and TabBarView.
in this screen, i have body content that retreive a list of element from sqllite using StreamBuilder. i get exact 100 elements ("finite list") to be shown using ListView.
my question, using ListView.builder, How we can jump to certain index when this screen opened ?
my main screen:
...
ScrollController controller = ScrollController();
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner : false,
home: DefaultTabController(
length: 3,
child: Scaffold(
appBar: AppBar(
backgroundColor: Pigment.fromString(UIData.primaryColor),
elevation: 0,
centerTitle: true,
title: Text(translations.text("quran").toUpperCase()),
bottom: TabBar(
tabs: [
Text("Tab1"),
Text("Tab2"),
Text("Tab3")
],
),
leading: Row(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
Expanded(
child: InkWell(
child: SizedBox(child: Image.asset("assets/images/home.png"), height: 10, width: 1,),
onTap: () => Navigator.of(context).pop(),
)
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _scrollToIndex,
tooltip: 'Testing Index Jump',
child: Text("GO"),
),
body:
TabBarView(
children: [
Stack(
children: <Widget>[
MyDraggableScrollBar.create(
scrollController: controller,
context: context,
heightScrollThumb: 25,
child: ListView(
controller: controller,
children: <Widget>[
Padding(
padding: EdgeInsets.fromLTRB(30, 15, 30, 8),
child: Container(
alignment: Alignment.center,
height: 30,
child: ClipRRect(
borderRadius: BorderRadius.circular(8),
child: TextField(
style: TextStyle(color: Colors.green),
decoration: new InputDecoration(
contentPadding: EdgeInsets.all(5),
border: InputBorder.none,
filled: true,
hintStyle: new TextStyle(color: Colors.green, fontSize: 14),
prefixIcon: Icon(FontAwesomeIcons.search,color: Colors.green,size: 17,),
hintText: translations.text("search-quran"),
fillColor: Colors.grey[300],
prefixStyle: TextStyle(color: Colors.green)
),
onChanged: (val) => quranBloc.searchSurah(val),
),
)
)
),
//surah list
streamBuilderQuranSurah(context)
],
)
) // MyDraggableScrollBar
],
),
Icon(Icons.directions_transit),
Icon(Icons.directions_bike),
],
)
)));
}
Widget streamBuilderQuranSurah(BuildContext ctx){
return StreamBuilder(
stream: quranBloc.chapterStream ,
builder: (BuildContext context, AsyncSnapshot<ChaptersModel> snapshot){
if(snapshot.hasData){
return ListView.builder(
controller: controller,
shrinkWrap: true,
physics: NeverScrollableScrollPhysics(),
itemCount:(snapshot.data.chapters?.length ?? 0),
itemBuilder: (BuildContext context, int index) {
var chapter =
snapshot.data.chapters?.elementAt(index);
return chapterDataCell(chapter);
},
);
}
else{
return SurahItemShimmer();
}
},
);
}
...
class MyDraggableScrollBar.dart :
import 'package:draggable_scrollbar/draggable_scrollbar.dart';
import 'package:flutter/material.dart';
class MyDraggableScrollBar {
static Widget create({
#required BuildContext context,
#required ScrollController scrollController,
#required double heightScrollThumb,
#required Widget child,
}) {
return DraggableScrollbar(
alwaysVisibleScrollThumb: true,
scrollbarTimeToFade: Duration(seconds: 3),
controller: scrollController,
heightScrollThumb: heightScrollThumb,
backgroundColor: Colors.green,
scrollThumbBuilder: (
Color backgroundColor,
Animation<double> thumbAnimation,
Animation<double> labelAnimation,
double height, {
Text labelText,
BoxConstraints labelConstraints,
}) {
return InkWell(
onTap: () {},
child: Container(
height: height,
width: 7,
color: backgroundColor,
),
);
},
child: child,
);
}
}
i have tried find other solutions but seems not working, for example indexed_list_view that only support infinite list
and it seems flutter still not have feature for this, see this issue
Any Idea ?
You can use https://pub.dev/packages/scrollable_positioned_list. You can pass the initial index to the widget.
ScrollablePositionedList.builder(
initialScrollIndex: 12, //you can pass the desired index here//
itemCount: 500,
itemBuilder: (context, index) => Text('Item $index'),
itemScrollController: itemScrollController,
itemPositionsListener: itemPositionsListener,
);
General Solution:
To store anything which can be represented as a number/string/list of strings, Flutter provides a powerful easy-to-use plugin which stores the values needed to be stored along with a key. So the next time you need you'll need to retrieve or even update that value all that you'll need is that key.
To get started, add the shared_preferences plugin to the pubspec.yaml file,
dependencies:
flutter:
sdk: flutter
shared_preferences: "<newest version>"
Run flutter pub get from the terminal or if your using IntelliJ just click on Packages get(You'll find it somewhere around the top-right corner of your screen while viewing the pubspec.yaml file)
Once the above command is successfully executed, import the below file in your main.dart or concerned file.
import 'package:shared_preferences/shared_preferences.dart';
Now just attach a ScrollController to your ListView.builder() widget and make sure that the final/last offset is stored along with a specific key using shared_preferences whenever the user leaves the app in any way and is set when the initState of your concerned widget is called.
In order to know to detect changes in the state of our app and to act with accordance to it, we'll be inheriting WidgetsBindingObserver to our class.
Steps to follow:
Extend the WidgetsBindingObserver class along with the State class of your StatefulWidget.
Define a async function resumeController() as a function member of the above class.
Future<void> resumeController() async{
_sharedPreferences = await SharedPreferences.getInstance().then((_sharedPreferences){
if(_sharedPreferences.getKeys().contains("scroll-offset-0")) _scrollController= ScrollController(initialScrollOffset:_sharedPreferences.getDouble("scroll-offset-0"));
else _sharedPreferences.setDouble("scroll-offset-0", 0);
setState((){});
return _sharedPreferences;
});
Declare two variables one to store and pass the scrollcontroller and the other to store and use the instance of SharedPreferences.
ScrollController _scrollController;
SharedPreferences _sharedPreferences;
Call resumeController() and pass your class to the addObserver method of the instance object in WidgetsBinding class.
resumeController();
WidgetsBinding.instance.addObserver(this);
Simply paste this code in the class definition (outside other member functions)
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
_scrollController.dispose();
super.dispose();
}
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
if(state==AppLifecycleState.paused || state==AppLifecycleState.inactive || state==AppLifecycleState.suspending)
_sharedPreferences.setDouble("scroll-offset-0", _scrollController.offset);
super.didChangeAppLifecycleState(state);
}
Pass the ScrollController() to the concerned Scrollable.
Working Example:
class MyWidget extends StatefulWidget {
#override
_MyWidgetState createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> with WidgetsBindingObserver{
//[...]
ScrollController _scrollController;
SharedPreferences _sharedPreferences;
Future<void> resumeController() async{
_sharedPreferences = await SharedPreferences.getInstance().then((_sharedPreferences){
if(_sharedPreferences.getKeys().contains("scroll-offset-0")) _scrollController= ScrollController(initialScrollOffset:_sharedPreferences.getDouble("scroll-offset-0"));
else _sharedPreferences.setDouble("scroll-offset-0", 0);
setState((){});
return _sharedPreferences;
});
}
#override
void initState() {
resumeController();
WidgetsBinding.instance.addObserver(this);
super.initState();
}
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
_scrollController.dispose();
super.dispose();
}
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
if(state==AppLifecycleState.paused || state==AppLifecycleState.inactive || state==AppLifecycleState.suspending)
_sharedPreferences.setDouble("scroll-offset-0", _scrollController.offset);
super.didChangeAppLifecycleState(state);
}
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
appBar: AppBar(
title: Text("Smart Scroll View"),
),
body: ListView.builder(
itemCount: 50,
controller: _scrollController,
itemBuilder: (c,i)=>
Padding(
padding: EdgeInsets.symmetric(horizontal: 24,vertical: 16),
child: Text((i+1).toString()),
),
),
),
);
}
}
Solution without knowing the size of your widgets
the Solution I found without knowing the size of your widget is displaying a reverse 'sublist' from the index to the end, then scroll to the top of your 'sublist' and reset the entire list. As it is a reverse list the item will be add at the top of the list and you will stay at your position (the index).
the problem is that you can't use a listView.builder because you will need to change the size of the list
example
class _ListViewIndexState extends State<ListViewIndex> {
ScrollController _scrollController;
List<Widget> _displayedList;
#override
void initState() {
super.initState();
_scrollController = ScrollController();
_displayedList = widget.items.sublist(0, widget.items.length - widget.index);
if (SchedulerBinding.instance.schedulerPhase == SchedulerPhase.persistentCallbacks) {
SchedulerBinding.instance.addPostFrameCallback((_) {
//here the sublist is already build
completeList();
});
}
}
completeList() {
//to go to the last item(in first position)
_scrollController.jumpTo(_scrollController.position.maxScrollExtent);
//reset the list to the full list
setState(() {
_displayedList = widget.items;
});
}
#override
Widget build(BuildContext context) {
return Stack(
children: <Widget>[
ListView(
controller: _scrollController,
reverse: true,
children: _displayedList,
),
]
);
}
}
The https://pub.dev/packages/indexed_list_view package could maybe help you out for this. Use something like this:
IndexedListView.builder(
controller: indexScrollController,
itemBuilder: itemBuilder
);
indexScrollController.jumpToIndex(10000);
I'll present another approach, which supports list lazy loading unlike #Shinbly 's method, and also support tiles in list to resize without recalculating the correct offset of the ListView nor saving any persistent information like "#Nephew of Stackoverflow" does.
The essential key to this approach is to utilize CustomScrollView, the CustomScrollView.center property.
Here's an example based on the example code from Flutter document (widgets.CustomScrollView.2):
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
List<int> top = [];
List<int> bottom = [0];
List<int> test = List.generate(10, (i) => -5 + i);
bool positionSwitcher = true;
#override
Widget build(BuildContext context) {
positionSwitcher = !positionSwitcher;
final jumpIndex = positionSwitcher ? 1 : 9;
Key centerKey = ValueKey('bottom-sliver-list');
return Scaffold(
appBar: AppBar(
title: const Text('Press Jump!! to jump between'),
leading: IconButton(
icon: const Icon(Icons.add),
onPressed: () {
setState(() {
top.add(-top.length - 1);
bottom.add(bottom.length);
});
},
),
),
body: Column(
children: [
Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
RaisedButton(
child: Text('Jump!!'),
onPressed: () => setState(() {}),
),
Text(positionSwitcher ? 'At top' : 'At bottom'),
],
),
Expanded(
child: CustomScrollView(
center: centerKey,
slivers: <Widget>[
SliverList(
delegate: SliverChildBuilderDelegate(
(BuildContext context, int i) {
final index = jumpIndex - 1 - i;
return Container(
alignment: Alignment.center,
color: Colors.blue[200 + test[index] % 4 * 100],
height: 100 + test[index] % 4 * 20.0,
child: Text('Item: ${test[index]}'),
);
},
childCount: jumpIndex,
),
),
SliverList(
key: centerKey,
delegate: SliverChildBuilderDelegate(
(BuildContext context, int i) {
final index = i + jumpIndex;
return Container(
alignment: Alignment.center,
color: i == 0
? Colors.red
: Colors.blue[200 + test[index] % 4 * 100],
height: 100 + test[index] % 4 * 20.0,
child: Text('Item: ${test[index]}'),
);
},
childCount: test.length - jumpIndex,
),
),
],
),
)
],
),
);
}
}
Explanation:
We use single list as data source for both SliverList
During each rebuild, we use center key to reposition the second SliverList inside ViewPort
Carefully manage the conversion from SliverList index to data source list index
Notice how the scroll view build the first SliverList by passing an index starting from bottom of this SliverList (i.e. index 0 suggests last item in the first list sliver)
Give the CustomeScrollView a proper key to decide whether to "re-position" or not
Working Example:
import 'dart:math';
import 'package:flutter/material.dart';
import 'package:scroll_to_index/scroll_to_index.dart';
class ScrollToIndexDemo extends StatefulWidget {
const ScrollToIndexDemo({Key? key}) : super(key: key);
#override
_ScrollToIndexDemoState createState() => _ScrollToIndexDemoState();
}
class _ScrollToIndexDemoState extends State<ScrollToIndexDemo> {
late AutoScrollController controller = AutoScrollController();
var rng = Random();
ValueNotifier<int> scrollIndex = ValueNotifier(0);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: ValueListenableBuilder(
valueListenable: scrollIndex,
builder: (context, index, child) {
return Text('Scroll Demo - $index');
},
),
),
body: ListView.builder(
itemCount: 100,
controller: controller,
itemBuilder: (context, index) {
return Padding(
padding: EdgeInsets.all(8),
child: AutoScrollTag(
key: ValueKey(index),
controller: controller,
index: index,
highlightColor: Colors.black.withOpacity(0.1),
child: Container(
padding: EdgeInsets.all(10),
alignment: Alignment.center,
color: Colors.grey[300],
height: 100,
child: Text(
'index: $index',
style: TextStyle(color: Colors.black),
),
),
),
);
},
),
floatingActionButton: FloatingActionButton(
onPressed: () async {
scrollIndex.value = rng.nextInt(100);
await controller.scrollToIndex(scrollIndex.value, preferPosition: AutoScrollPosition.begin);
},
tooltip: 'Increment',
child: Center(
child: Text(
'Next',
textAlign: TextAlign.center,
),
),
),
);
}
}
You can use the flutter_scrollview_observer lib to implement your desired functionality without invasivity
Create and use instance of ScrollController normally.
ScrollController scrollController = ScrollController();
ListView _buildListView() {
return ListView.builder(
controller: scrollController,
...
);
}
Create an instance of ListObserverController pass it to ListViewObserver
ListObserverController observerController = ListObserverController(controller: scrollController);
ListViewObserver(
controller: observerController,
child: _buildListView(),
...
)
Now you can scroll to the specified index position
// Jump to the specified index position without animation.
observerController.jumpTo(index: 1)
// Jump to the specified index position with animation.
observerController.animateTo(
index: 1,
duration: const Duration(milliseconds: 250),
curve: Curves.ease,
);
Hamburger icon color of navigation drawer is not changing. Its black by default. I want to change the this icon color in flutter, I am stuck, help me to change this icon color. here is my code.
class Test extends StatefulWidget {
#override
_TestState createState() => new _TestState();
}
class _TestState extends State<Test> {
#override
Widget build(BuildContext context) {
return new Scaffold(
drawer: new Drawer(),
appBar: new AppBar(
title: new Text("Navigation Drawer")
),
),
);
}
}
Add iconTheme to your AppBar
#override
Widget build(BuildContext context) {
return Scaffold(
drawer: Drawer(),
appBar: AppBar(
title: Text("Navigation Drawer"),
iconTheme: IconThemeData(color: Colors.green),
),
);
}
You can also check other solutions here.
You can also use following in Theme's data property
Theme(
data: ThemeData(primaryIconTheme: IconThemeData(color: Colors.red)), // use this
child: Scaffold(),
)
Or
appBar: AppBar(
leading: IconButton(
icon: Icon(Icons.menu, color: Colors.red), // set your color here
onPressed: () {},
),
),
To change color of your icon use this
#override
Widget build(BuildContext context) {
return new MaterialApp(
home: new Scaffold(
appBar: AppBar(title: new Text('List view example'),
leading: new Icon(Icons.menu,color: Colors.green,),
),
),
);
}
Icon(Icons.menu,color: Colors.green,) define color inside Icon
Use iconTheme in Appbar like this:
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text("App Bar"),
iconTheme: IconThemeData(color: Colors.black),
),
drawer: Drawer(),
);
}
This is the only solution to make the button clickable otherwise you need to openDrawer onTap.
AppBar(
iconTheme: const IconThemeData(
size: 40, //change size on your need
color: Colors.black, //change color on your need
),
),
Using The iconTheme for Appbar is not currently working with useMaterial3 = true, And all these answers defined a leading icon for the Appbar without telling how to implement it's onPress behavior, So the best way to change the Drawers icon or it's color is this :
Declare the key for Scaffold :
final scaffoldKey = GlobalKey<ScaffoldState>();
And apply it to Scaffold:
Scaffold(
key: scaffoldKey,
drawer: Drawer()
)
Then , Apply the drawer icon like below with click action:
AppBar(
title: Text("My AppBar"),
leading: IconButton(
icon: Icon(Icons.person),
onPressed: (){
if(scaffoldKey.currentState!.isDrawerOpen){
scaffoldKey.currentState!.closeDrawer();
//close drawer, if drawer is open
}else{
scaffoldKey.currentState!.openDrawer();
//open drawer, if drawer is closed
}
},
),
)
You can change it from main.dart easily this way-
return MaterialApp(
title: 'XYZ',
debugShowCheckedModeBanner: false,
theme: ThemeData(
appBarTheme: AppBarTheme(
iconTheme: IconThemeData(color: Colors.black),
actionsIconTheme: IconThemeData(color: Colors.blue),
backgroundColor: theme.backgroundColor,
elevation: 0,
),
),