Flutter Argument passing - Getting a null from routeArgs - flutter

Question

I have the following setup of my flutter app:
HomeScreen.Dart
Widget build(BuildContext context) {
return Scaffold(
appBar: homeAppBar(context),
bottomNavigationBar: BottomNavBar(),
body: SingleChildScrollView(
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
CategoryList(),
ItemList(),
],
),
));
}
}
The CategoryList class contains a list view of category items. When a category item is clicked, the associated products should be displayed for that item. The way I do that is by passing the category name to the product item list class. Please see below:
CategoryItem.dart
class CategoryItemN extends StatelessWidget {
final String title;
const CategoryItemNew({
#required this.title,
});
#override
Widget build(BuildContext context) {
return GestureDetector(
onTap: () => selectCategory(context),
child: Padding(
padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 15),
child: Column(
children: <Widget>[
Text(
title,
style: isActive
? TextStyle(
color: kTextColor,
fontWeight: FontWeight.bold,
)
: TextStyle(fontSize: 12),
),
if (isActive)
Container(
margin: EdgeInsets.symmetric(vertical: 5),
height: 3,
width: 22,
decoration: BoxDecoration(
color: kPrimaryColor,
borderRadius: BorderRadius.circular(10),
),
),
],
),
),
);
}
void selectCategory(BuildContext ctx) {
Navigator.of(ctx).pushNamed(
ItemList.routeName,
arguments: {
'title': title ==== > This is the category name
},
);
}
}
ItemList.dart
class _ItemListState extends State<ItemList> {
var _isInit = true;
var _isLoading = false;
var title = '';
void didChangeDependencies() {
if (_isInit) {
setState(() {
_isLoading = true;
});
final routeArgs =
ModalRoute.of(context).settings.arguments as Map<String, String>;
title = routeArgs['title']; ===================> This is where the error occurs!
Provider.of<Products>(context).fetchProducts(title, true).then((_) {
setState(() {
_isLoading = false;
});
});
}
_isInit = false;
super.didChangeDependencies();
}
Here's the error message:
The following NoSuchMethodError was thrown building Listener: The method '[]' was called on null. Receiver: null Tried calling []("title")

Answer 1

You can get arguments through 'ModalRoute.of(context).settings.arguments' in the build().
final routeArgs =
ModalRoute.of(context).settings.arguments as Map<String, String>;
There is a official example about 'Pass arguments to a named route'.
https://flutter.dev/docs/cookbook/navigation/navigate-with-arguments