I'm new to using flutter and i was trying to implement a covid 19 tracker of cases in the world and i got this error when creating a custom widget to display number of cases , can anyone help me figure out the solution to this exactly as i have been trying to fix it for hours now.
This is the exception caught by the widgets library:
Error: Could not find the correct Provider above this NewCasesCard Widget
To fix, please:
Ensure the Provider is an ancestor to this NewCasesCard Widget
Provide types to Provider
Provide types to Consumer
Provide types to Provider.of()
Ensure the correct context is being used.
If none of these solutions work, please file a bug at:
https://github.com/rrousselGit/provider/issues
Here is the code:
import 'package:stay_safe/Providers/AppBrain.dart';
import 'package:stay_safe/utils/theme.dart';
import 'package:flutter/material.dart';
import 'package:flutter_spinkit/flutter_spinkit.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:provider/provider.dart';
class NewCasesCard extends StatelessWidget {
#override
Widget build(BuildContext context) {
return getCard(context);
}
Widget getCard(context){
if (Provider.of<AppBrain>(context).isloading2)
return Padding(
padding: const EdgeInsets.all(8.0),
child: Center(
child: SpinKitPumpingHeart(color: AppTheme().kcolors[0],),
),
);
else {
final countryInfo = Provider.of<AppBrain>(context).countryStats['countrydata'][0];
return Padding(
padding: const EdgeInsets.all(8.0),
child: Card(
elevation: 0.5,
color: Colors.white70,
child: Column(
children: <Widget>[
Padding(
padding: const EdgeInsets.all(8.0),
child: Text('New Cases Today',style: GoogleFonts.cabin(fontSize: 25),),
),
SizedBox(height: 8,),
Padding(
padding: const EdgeInsets.all(16.0),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
children: <Widget>[
StatIcon(countryInfo['total_active_cases'], 'Active', AppTheme().kcolors[0]),
StatIcon(countryInfo['total_new_cases_today'], 'New Cases', AppTheme().kcolors[2]),
StatIcon(countryInfo['total_new_deaths_today'], 'Deaths', AppTheme().kcolors[1])
],),
)
],
),
),
);
}
}
}
Widget StatIcon(int count,String type,Color color){
return Column(
children: <Widget>[
Text(count.toString(),style: GoogleFonts.cabin(color: color,fontWeight: FontWeight.bold,fontSize: 20),),
Text(type,style: GoogleFonts.cabin(color: color,fontWeight: FontWeight.bold,fontSize: 20),),
],
);
}
The issue looks like you have created the AppBrain provider in a different part of your widget tree to NewCasesCard, so when NewCasesCard attempts to find the provider by searching the tree it cannot. You need to make sure that the AppBrain provider is above NewCasesCard somewhere in the widget tree. So for example in the screen that includes this widget you could have:
class NewCasesScreen extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Provider<AppBrain>(
create: (_) => AppBrain(),
child: Scaffold(
body: ListView(
children: [
NewCasesCard(),
...
]
),
),
);
}
Alternatively you could initialise the provider at the top of your app since, from the name, it looks like it is used throughout. For this you could utilise the MultiProvider and have:
(Example taken from the package readme)
void main {
runApp(MultiProvider(
providers: [
Provider<AppBrain>(create: (_) => AppBrain()),
Provider<SomethingElse>(create: (_) => SomethingElse()),
],
child: MaterialApp(...),
));
}
This way you can be sure that the provider will always be found.
Related
I want make text to the right, what am I doing so far
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
static const String _judul = 'Private Chat';
static var _warnaTema = Colors.pink[100];
Widget _dummyExpanded() {
return Expanded(
child: Container(), //contain empty data,
); //just for fill remaining space
}
#override
Widget build(BuildContext context) {
return MaterialApp(
title: _judul,
theme: ThemeData(
primaryColor: _warnaTema,
),
home: Column(
children: [
Container(
child: Row(
children: [
this._dummyExpanded(),
Text('this is real data 1'),
],
),
),
Container(
child: Row(
children: [
this._dummyExpanded(),
Text('this is real data 2'),
],
),
)
],
),
);
}
}
The layout output is what I expected (the text is in right), however there's unneeded code.
As you see I use unnecessary method _dummyExpanded to fill
available space which it's just expanded with empty container. Of course it will be hard to read since there are many nested row and column, how I remove that unneeded method without loss layout output what I expect?
I believe I should have use alignment but I don't know how to
Method 1.
Container(
child: Row(
mainAxisAlignment:MainAxisAlignment.end,
children: [
Text('this is real data 2'),
],
),
)
Method 2.
I prefer this method, You can wrap text with this method.
You can also use Flexible widget instead of Expanded
Container(
child: Row(
children: [
Expanded(child: Text('this is real data 2', textAlign:TextAlign.end )),
],
),
)
Method 3.
If you have only Text widgets as children of Column widget then you can set crossAxisAlignment: CrossAxisAlignment.end, for your parent Column widget.
First, let me start with I am new to Flutter and this is my first app.
I am running into an issue where I am getting the error:
════════ Exception caught by rendering library ═════════════════════════════════
A RenderFlex overflowed by 24 pixels on the bottom.
The relevant error-causing widget was
Column
lib/widgets/home_screen_cta.dart:42
════════════════════════════════════════════════════════════════════════════════
For the 4 buttons on my home screen.
The weird part is the screen looks fine. No yellow and black bars or anything. This only happens when I transition from the login screen to the home screen. If I move around the app, this does not happen. I do notice it on another form once it is submitted (only for the first submission, not for any others). It also looks bad for the first animation but after that it looks fine.
I was wondering if I should just ignore this but it seems like that is a bad idea.
I have tried changing this to use many other options. This includes:
Changed between Expanded and Flexible
Tried using a container/SizedBox instead
Tried to find another solution for the CTA Item but couldn't find anything that would do this look
At this point, I understand it's a overflow issue but there are no indications of an overflow appearing in the app.
I am trying to make the app responsive in nature so I believe I am doing okay for that. This RenderFlex overflow issue is really puzzling. The fact I don't see the yellow/black bars in the app makes me think this is happening during a transition and I wonder if I should be concerned about it?
Is there a way to control these animations? I really do not like them and I feel it's the transition causing the overflow issue... I'm a bit lost on this.
My code:
Home Screen (HomeDashboard):
import 'package:flutter/material.dart';
import '../app/components/app_drawer.dart';
import '../app/components/app_bar.dart';
import '../lang/app_localizations.dart';
import '../widgets/clock_text.dart';
import '../widgets/home_screen_cta.dart';
import '../widgets/home_screen_dashboard.dart';
import '../widgets/logo_horizontal.dart';
class HomeDashboard extends StatelessWidget {
const HomeDashboard({Key? key}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: FreshFlowAppBar.get(title: AppLocalizations.of(context)!.title),
drawer: const AppDrawer(),
body: Padding(
padding: const EdgeInsets.all(8.0),
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: const [
Flexible(
flex: 1,
fit: FlexFit.loose,
child: LogoHorizontal(),
),
Flexible(
flex: 1,
fit: FlexFit.loose,
child: ClockText(),
),
Flexible(
flex: 6,
fit: FlexFit.tight,
child: HomeScreenDashboard(),
),
Flexible(
flex: 1,
fit: FlexFit.tight,
child: HomeScreenCta(),
),
],
),
),
),
);
}
}
HomeScreenCta:
import 'package:flutter/material.dart';
import 'package:flutter_font_icons/flutter_font_icons.dart';
import 'package:fresh_flow/services/user.service.dart';
import 'package:provider/provider.dart';
import '../lang/app_localizations.dart';
import '../screens/home/pre_op_entry.dart';
import '../screens/home/prod_entry.dart';
import '../screens/home/post_op_entry.dart';
import '../screens/home/downtime_entry.dart';
import '../services/pre-op.service.dart';
import '../utils/size_helpers.dart';
class HomeScreenCta extends StatefulWidget {
const HomeScreenCta({Key? key}) : super(key: key);
#override
State<HomeScreenCta> createState() => _HomeScreenCtaState();
}
class _HomeScreenCtaState extends State<HomeScreenCta> {
bool _isPreOpSetupCompleted = false;
/// Returns a Widget for the CTA item
Widget _getCtaItem(
BuildContext context,
String title,
IconData iconData,
String routeName,
bool isEnabled,
) {
return GestureDetector(
onTap: () {
if (isEnabled) {
Navigator.of(context).pushNamed(routeName);
}
},
child: Opacity(
opacity: isEnabled ? 1.0 : 0.4,
child: Column( // This is causing RenderFlex overflow issue
children: [
Icon(
iconData,
size: displayHeight(context) * .05,
),
const SizedBox(
height: displayHeight(context) * .03,
),
Text(
title,
style: TextStyle(
fontSize: displayWidth(context) * 0.03,
),
)
],
),
),
);
}
#override
Widget build(BuildContext context) {
final l10n = AppLocalizations.of(context);
// Define services
final _preOpService = Provider.of<PreOpService>(
context,
listen: false, // No need to listen
);
final _userService = Provider.of<UserService>(
context,
listen: false, // No need to listen
);
_preOpService.init(_userService.getId()!);
// Only Pre-Op Entry is allowed until it is complete all others need to be disabled
if (_preOpService.hasCompletedFirstPreopOfTheDay()) {
setState(() {
_isPreOpSetupCompleted = true;
});
}
final _width =
(displayWidth(context) - MediaQuery.of(context).padding.left) *
0.24;
final _children = [
SizedBox(
width: _width,
child: _getCtaItem(
context,
l10n!.preOpEntry,
FontAwesome.wrench,
PreOpEntry.routeName,
true,
),
),
SizedBox(
width: _width,
child: _getCtaItem(
context,
l10n.prodEntry,
MaterialCommunityIcons.account_hard_hat,
ProdEntry.routeName,
_isPreOpSetupCompleted,
),
),
SizedBox(
width: _width,
child: _getCtaItem(
context,
l10n.postOpEntry,
Icons.task_alt,
PostOpEntry.routeName,
_isPreOpSetupCompleted,
),
),
SizedBox(
width: _width,
child: _getCtaItem(
context,
l10n.downtimeEntry,
Icons.flag_sharp,
DowntimeEntry.routeName,
_isPreOpSetupCompleted,
),
),
];
return Center(
child: Row(
// mainAxisAlignment: MainAxisAlignment.center,
children: _children,
),
);
}
}
Hi I'm learning Flutter,
below is the design which I'm trying to achieve,
Could I get the code snippet for first row, so that basing on that I'll try to create remaining here is github https://github.com/phanivaranasi/blood_donar.git pages/dashboard.dart
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:red_cross_hyd/components/header.dart';
import 'package:red_cross_hyd/pages/login.dart';
class DashboardPage extends StatefulWidget {
#override
DashboardPageState createState() => DashboardPageState();
}
class DashboardPageState extends State<DashboardPage> {
#override
Widget build(BuildContext context) {
final content = Scaffold(
appBar: header,
body: SingleChildScrollView(
child: new Stack(
children: <Widget>[
Container(
padding: EdgeInsets.fromLTRB(10, 10, 10, 10),
height: 120,
width: double.maxFinite,
child: Stack(
children: <Widget>[
],
)
),
],
)));
return content;
//return new WillPopScope(child: content, onWillPop: () async => false);
}
}
Icons CC: [Flat Icons](https://www.flaticon.com/]
I request you to please update your question, with the issue you are facing. Flutter provides multiple widgets that can help with the layout shown above. The GridView Widget seems to be a perfect fit for the UI shown above.
I'm trying to use the simple state management described in the Flutter docs, using a ChangeNotifier, a Consumer, and a ChangeNotifierProvider.
My problem is that I can't get a hold a on valid context to update my model (details below...). I get an error:
Error: Error: Could not find the correct Provider above this CreateOrganizationDialog Widget
This likely happens because you used a BuildContext that does not include the provider of your choice. There are a few common scenarios:
The provider you are trying to read is in a different route.
Providers are "scoped". So if you insert of provider inside a route, then other routes will not be able to access that provider.
You used a BuildContext that is an ancestor of the provider you are trying to read.
Make sure that CreateOrganizationDialog is under your MultiProvider/Provider.
This usually happen when you are creating a provider and trying to read it immediately.
Here are extracts of my code:
class OrganizationModel extends ChangeNotifier {
final List<Organization> _items = [];
/// An unmodifiable view of the items in the cart.
UnmodifiableListView<Organization> get items => UnmodifiableListView(_items);
void addList(List<Organization> items) {
_items.addAll(items);
notifyListeners();
}
}
This is my model.
class OrganizationBodyLayout extends StatelessWidget {
Future<void> _showCreateOrganizationDialog() async {
return showDialog<void>(
context: navigatorKey.currentState.overlay.context,
barrierDismissible: false,
child: CreateOrganizationDialog());
}
_onCreateOrganizationPressed() {
_showCreateOrganizationDialog();
}
_onDeleteOrganizationPressed() {
//TODO something
}
_onEditOrganizationPressed() {
//TODO something
}
#override
Widget build(BuildContext context) {
return Container(
child: Column(mainAxisSize: MainAxisSize.max, children: [
ButtonBar(
alignment: MainAxisAlignment.start,
mainAxisSize: MainAxisSize.max,
children: <Widget>[
RaisedButton(
onPressed: _onCreateOrganizationPressed,
child: Text("New Organization"),
),
],
),
Expanded(
child: Container(
color: Colors.pink,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: <Widget>[
Expanded(
child: ChangeNotifierProvider(
create: (context) => OrganizationModel(),
child: OrganizationListView(),
)),
Expanded(child: Container(color: Colors.brown))
]))),
]));
}
}
A stateless widget that contains a ChangeNotifierProvider just on top of the list widget using the model.
On a button click, a modal dialog is shown, then data is fetched from the network. I should then update my model calling the addList operation.
Below is the code for the stateful dialog box.
class CreateOrganizationDialog extends StatefulWidget {
#override
_CreateOrganizationDialogState createState() =>
_CreateOrganizationDialogState();
}
class _CreateOrganizationDialogState extends State<CreateOrganizationDialog> {
TextEditingController _nametextController;
TextEditingController _descriptionTextController;
#override
initState() {
_nametextController = new TextEditingController();
_descriptionTextController = new TextEditingController();
super.initState();
}
#override
Widget build(BuildContext context) {
return Dialog(
child: Container(
width: 200,
height: 220,
child: Column(
children: [
Text('New organization',
style: Theme.of(context).textTheme.headline6),
Padding(
padding: EdgeInsets.all(8.0),
child: TextFormField(
decoration: new InputDecoration(hintText: "Organization name"),
controller: _nametextController,
),
),
Padding(
padding: EdgeInsets.all(8.0),
child: TextFormField(
decoration:
new InputDecoration(hintText: "Organization description"),
controller: _descriptionTextController,
),
),
ButtonBar(
children: [
FlatButton(
child: new Text("Cancel"),
onPressed: () {
Navigator.of(context).pop();
},
),
FlatButton(
child: new Text("Create"),
onPressed: () {
setState(() {
Future<Organization> organization =
backendCreateOrganization(_nametextController.text,
_descriptionTextController.text);
organization.then((value) {
Future<List<Organization>> organizations =
backendReloadOrganizations();
organizations.then((value) {
var model = context.read<OrganizationModel>();
// var model = navigatorKey.currentState.overlay.context.read<OrganizationModel>();
//model.addList(value);
});
});
});
Navigator.of(context).pop();
//context is the one for the create dialog here
},
)
],
)
],
),
));
}
}
My problem happens at the line
var model = context.read<OrganizationModel>();
Thinking of it, the context available here is the modal dialog box context - so it's kind of logical that the Provider is not found in the widget tree.
However, I can't see how to retrieve the proper context (which would be the one for the result list view, where the Provider is located) in order to get the model and then update it.
Any idea is welcome :-)
Solved (kind of).
The only way I've found to solve this is by making my model a global variable:
var globalModel = OrganizationModel();
And referencing this global model in all widgets that consume it. I can't find a way to find the context of a stateless widget from within a callback in another stateful widget.
It works, but it's ugly. Still open to elegant solutions here :-)
Get_it seems to be elegant way of sharing models across the application. Please check the documentation for the different use cases they provide.
You could do something like the following
GetIt getIt = GetIt.instance;
getIt.registerSingleton<AppModel>(AppModelImplementation());
getIt.registerLazySingleton<RESTAPI>(() =>RestAPIImplementation());
And in other parts of your code, you could do something like
var myAppModel = getIt.get<AppModel>();
I'm working on my first Flutter app (debugging on my Android phone). I have a list with row items. When you long-press the row, it copies the content into the user's clipboard. This is working great!
But I need to let the user know that the content was copied.
I've attempted to follow many tutorials on trying to get the row surrounded by a build method or inside a Scaffold, but I can't get any to work. Is there an alternative method to notifying the user (simply) that something like "Copied!" took place?
Notice the commented out Scaffold.of(... below. It just seems like there must be an easier method to notifying the user other than wrapping everything in a Scaffold. (and when I try, it breaks my layout).
import 'package:flutter/material.dart';
import 'package:my_app/Theme.dart' as MyTheme;
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/services.dart';
class RowRule extends StatelessWidget {
final DocumentSnapshot ruleGroup;
RowRule(this.ruleGroup);
_buildChildren() {
var builder = <Widget>[];
if (!ruleGroup['label'].isEmpty) {
builder.add(new Text(ruleGroup['label'],
style: MyTheme.TextStyles.articleContentLabelTextStyle));
}
if (!ruleGroup['details'].isEmpty) {
builder.add(new Text(ruleGroup['details'],
style: MyTheme.TextStyles.articleContentTextStyle));
}
return builder;
}
#override
Widget build(BuildContext context) {
return new GestureDetector(
onLongPress: () {
Clipboard.setData(new ClipboardData(text: ruleGroup['label'] + " " + ruleGroup['details']));
// Scaffold.of(context).showSnackBar(SnackBar
// (content: Text('text copied')));
},
child: Container(
margin: const EdgeInsets.symmetric(vertical: 3.0),
child: new FlatButton(
color: Colors.white,
padding: EdgeInsets.symmetric(horizontal: 0.0),
child: new Stack(
children: <Widget>[
new Container(
margin: const EdgeInsets.symmetric(
vertical: MyTheme.Dimens.ruleGroupListRowMarginVertical),
child: new Container(
child: Padding(
padding: EdgeInsets.symmetric(horizontal: 32.0, vertical: 8.0),
child: new Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: _buildChildren(),
),
)),
)
],
),
),
));
}
}
The goal is to have a page like this (see image), which I have, and it works and scrolls...etc, but I cannot get it to work with a Scaffold, and therefore, haven't been able to use the snackbar. Each "Row" (which this file is for) should show a snackbar on longPress.
You can use GlobalKey to make it work the way you want it.
Since I don't have access to your database stuff, this is how I gave you an idea to do it. Copy and paste this code in your class and make changes accordingly. I also believe there is something wrong in your RowRule class, can you just copy the full code I have given you and run?
void main() => runApp(MaterialApp(home: HomePage()));
class HomePage extends StatelessWidget {
final GlobalKey<ScaffoldState> _key = GlobalKey();
#override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Color(0xFFFFFFFF).withOpacity(0.9),
key: _key,
body: Column(
children: <Widget>[
Container(
color: Color.fromRGBO(52, 56, 245, 1),
height: 150,
alignment: Alignment.center,
child: Container(width: 56, padding: EdgeInsets.only(top: 12), decoration: BoxDecoration(shape: BoxShape.circle, color: Colors.yellow)),
),
Expanded(
child: ListView.builder(
padding: EdgeInsets.zero,
itemCount: 120,
itemBuilder: (context, index) {
return Container(
color: Colors.white,
margin: const EdgeInsets.all(4),
child: ListTile(
title: Text("Row #$index"),
onLongPress: () => _key.currentState
..removeCurrentSnackBar()
..showSnackBar(SnackBar(content: Text("Copied \"Row #$index\""))),
),
);
},
),
),
],
),
);
}
}
These is a simple plugin replacement for the Snackbar named "Flushbar".
You can get the plugin here - https://pub.dartlang.org/packages/flushbar
You don't have to take care of any wrapping of widgets into scaffold also you get a lot of modifications for you like background gradient, adding forms and so on into Snackbar's and all.
Inside your onLongPressed in GestureDetectore you can do this.
onLongPressed:(){
Clipboard.setData(new ClipboardData(text: ruleGroup['label'] + " " + ruleGroup['details']));
Flushbar(
message: "Copied !!",
duration: Duration(seconds: 3),
)..show(context);
}
This will display the snackbar in you app where you would want to see it also you can get a lot of modification available to you so the you can make it look as per your app.
There are couple of things you need to do, like use onPressed property of the FlatButton it is mandatory to allow clicks, wrap your GestureDetector in a Scaffold. I have further modified the code so that it uses GlobalKey to make things easy for you.
Here is the final code (Your way)
class RowRule extends StatelessWidget {
final GlobalKey<ScaffoldState> globalKey = GlobalKey();
final DocumentSnapshot ruleGroup;
RowRule(this.ruleGroup);
_buildChildren() {
var builder = <Widget>[];
if (!ruleGroup['label'].isEmpty) {
builder.add(new Text(ruleGroup['label'], style: MyTheme.TextStyles.articleContentLabelTextStyle));
}
if (!ruleGroup['details'].isEmpty) {
builder.add(new Text(ruleGroup['details'], style: MyTheme.TextStyles.articleContentTextStyle));
}
return builder;
}
#override
Widget build(BuildContext context) {
return Scaffold(
key: globalKey,
body: GestureDetector(
onLongPress: () {
Clipboard.setData(new ClipboardData(text: ruleGroup['label'] + " " + ruleGroup['details']));
globalKey.currentState
..removeCurrentSnackBar()
..showSnackBar(SnackBar(content: Text('text copied')));
},
child: Container(
margin: const EdgeInsets.symmetric(vertical: 3.0),
child: new FlatButton(
onPressed: () => print("Handle button press here"),
color: Colors.white,
padding: EdgeInsets.symmetric(horizontal: 0.0),
child: new Stack(
children: <Widget>[
new Container(
margin: const EdgeInsets.symmetric(vertical: MyTheme.Dimens.ruleGroupListRowMarginVertical),
child: new Container(
child: Padding(
padding: EdgeInsets.symmetric(horizontal: 32.0, vertical: 8.0),
child: new Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: _buildChildren(),
),
),
),
)
],
),
),
),
),
);
}
}
I made a dropdown banner package on pub that allows you to easily notify users of errors or confirmation of success. It's a work in progress as I continue to add visually rich features.
I am not sure if your build() method is completed or you are yet to change it, because it consist of many widgets which are just redundant. Like there is no need to have Container in Container and further Padding along with a FlatButton which would make complete screen clickable. Also having Column won't be a good idea because your screen may overflow if you have more data. Use ListView instead.
So, if you were to take my advice, use this simple code that should provide you what you are really looking for. (See the build() method is of just 5 lines.
class RowRule extends StatelessWidget {
final GlobalKey<ScaffoldState> globalKey = GlobalKey();
final DocumentSnapshot ruleGroup;
RowRule(this.ruleGroup);
_buildChildren() {
var builder = <Widget>[];
if (!ruleGroup['label'].isEmpty) {
builder.add(
ListTile(
title: Text(ruleGroup['label'], style: MyTheme.TextStyles.articleContentLabelTextStyle),
onLongPress: () {
globalKey.currentState
..removeCurrentSnackBar()
..showSnackBar(SnackBar(content: Text("Clicked")));
},
),
);
}
if (!ruleGroup['details'].isEmpty) {
builder.add(
ListTile(
title: Text(ruleGroup['details'], style: MyTheme.TextStyles.articleContentTextStyle),
onLongPress: () {
globalKey.currentState
..removeCurrentSnackBar()
..showSnackBar(SnackBar(content: Text("Clicked")));
},
),
);
}
return builder;
}
#override
Widget build(BuildContext context) {
return Scaffold(
key: globalKey,
body: ListView(children: _buildChildren()),
);
}
}
I read your comments on all answers and here is my conslusion:
You need ScaffoldState object that is just above the widget in tree to show Snackbar. You can either get it through GlobalKey as many have suggested. Fairly simple if the Scaffold is created inside build of the widget, but if it is outside the widget (in your case) then it becomes complicated. You need to pass that key, wherever you need it through Constructor arguments of child widgets.
Scaffold.of(context) is a very neat way to just do that. Just like an InheritedWidget, Scaffold.of(BuildContext context) gives you access of the closest ScaffoldState object above the tree. Else it could be a nightmare to get that instance (by passing it through as constructor arguments) if your tree was very deep.
Sorry, to disappoint but I don't think there is any better or cleaner method than this, if you want to get the ScaffoldState that is not built inside build of that widget. You can call it in any widget that has Scaffold as a parent.