Can´t pass null variable between two pages in flutter - dart

Question

I´m trying to navigate between two pages. In second page I need a constructor so i need to declare the variable null in first page and initialize it in the second page.
In main.dart (first page) i have similar to
PostDetailsPage.tag: (context) => PostDetailsPage(new List()),
In the second page (PostDetailsPage) i have this
final List<charts.Series> seriesList;
final bool animate;
PostDetailsPage(this.seriesList, {this.animate});
When i go to page two return
< List < Series< dynamic, dynamic > > is not a subtype of type < List < Series< dynamic, String>>
So how can i solve? Initializate the value in first page and pass it? Initializate value as null in first page and pass it?
UPDATED
Main.dart class
import 'package:flutter/material.dart';
import 'package:fluttercrud/screens/login_page.dart';
import 'package:fluttercrud/screens/home_page.dart';
import 'package:fluttercrud/screens/partials/list_post.dart';
import 'package:fluttercrud/screens/maps_page.dart';
import 'package:fluttercrud/screens/post_details_page.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
final routes = <String, WidgetBuilder>{
LoginPage.tag: (context) => LoginPage(),
HomePage.tag: (context) => HomePage(),
ListPost.tag: (context) => ListPost(),
MapsPage.tag: (context) => MapsPage(),
PostDetailsPage.tag: (context) => PostDetailsPage(new List()),
};
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'iGota',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch : Colors.blue,
),
home: LoginPage(),
routes: routes,
);
}
}
PostDetailsPage.dart class
import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
class PostDetailsPage extends StatelessWidget{
static String tag = 'post-details-page';
final List<charts.Series> seriesList;
final bool animate;
PostDetailsPage(this.seriesList, {this.animate});
/// Creates a [BarChart] with sample data and no transition.
factory PostDetailsPage.withSampleData() {
return new PostDetailsPage(
_createSampleData(),
// Disable animations for image tests.
animate: false,
);
}
#override
Widget build(BuildContext context) {
return new charts.BarChart(
seriesList,
animate: animate,
);
}
/// Create one series with sample hard coded data.
static List<charts.Series<OrdinalSales, String>> _createSampleData() {
final data = [
new OrdinalSales('2014', 5),
new OrdinalSales('2015', 25),
new OrdinalSales('2016', 100),
new OrdinalSales('2017', 75),
];
return [
new charts.Series<OrdinalSales, String>(
id: 'Sales',
colorFn: (_, __) => charts.MaterialPalette.blue.shadeDefault,
domainFn: (OrdinalSales sales, _) => sales.year,
measureFn: (OrdinalSales sales, _) => sales.sales,
data: data,
)
];
}
}
/// Sample ordinal data type.
class OrdinalSales {
final String year;
final int sales;
OrdinalSales(this.year, this.sales);
}
UPDATED 2: FIXED
Main.dart
import 'package:flutter/material.dart';
import 'package:fluttercrud/screens/login_page.dart';
import 'package:fluttercrud/screens/home_page.dart';
import 'package:fluttercrud/screens/partials/list_post.dart';
import 'package:fluttercrud/screens/maps_page.dart';
import 'package:fluttercrud/screens/post_details_page.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
final routes = <String, WidgetBuilder>{
LoginPage.tag: (context) => LoginPage(),
HomePage.tag: (context) => HomePage(),
ListPost.tag: (context) => ListPost(),
MapsPage.tag: (context) => MapsPage(),
PostDetailsPage.tag: (context) => PostDetailsPage(),
};
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'iGota',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch : Colors.blue,
),
home: LoginPage(),
routes: routes,
);
}
}
PostDetailsPage.dart
import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
class PostDetailsPage extends StatefulWidget {
static String tag = 'post-details-page';
#override
PostDetailsPageState createState() => new PostDetailsPageState();
}
class PostDetailsPageState extends State<PostDetailsPage> {
List<charts.Series> seriesList = [];
bool animate;
void initState() {
super.initState();
seriesList = _createSampleData();
animate = false;
}
#override
Widget build(BuildContext context) {
return new Container(
decoration: new BoxDecoration(color: Colors.white),
child: new charts.BarChart(
seriesList,
animate: animate,
),
);
}
/// Create one series with sample hard coded data.
static List<charts.Series<OrdinalSales, String>> _createSampleData() {
final data = [
new OrdinalSales('2014', 5),
new OrdinalSales('2015', 25),
new OrdinalSales('2016', 100),
new OrdinalSales('2017', 75),
];
return [
new charts.Series<OrdinalSales, String>(
id: 'Sales',
colorFn: (_, __) => charts.MaterialPalette.blue.shadeDefault,
domainFn: (OrdinalSales sales, _) => sales.year,
measureFn: (OrdinalSales sales, _) => sales.sales,
data: data,
)
];
}
}
/// Sample ordinal data type.
class OrdinalSales {
final String year;
final int sales;
OrdinalSales(this.year, this.sales);
}

Answer 1

You can fix your issue by explicitly declaring the type on the List when you pass it in.
PostDetailsPage.tag: (context) => PostDetailsPage(List<charts.Series<dynamic, String>>()),
Or, you can explicitly declare the type of the list itself on the page itself:
final List<charts.Series<dynamic, String>> seriesList;
I think the intended way for the charts library to work is that you pass in an already initialized list of chart data, which the page then renders. If you want to return just with the given sample data, you should just use the given factory method PostDetailsPage.withSampleData().