Your Second Flutter App
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Next episode: 34. Lift State Up
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An InheritedWidget is useful for lifting state up because it can be accessed by any widget in the widget tree.
import 'package:flutter/material.dart';
class FilterStateContainer extends StatefulWidget {
}
final Widget child;
const FilterStateContainer({Key? key, required this.child}) : super(key: key);
@override
State<StatefulWidget> createState() => FilterState();
class FilterState extends State<FilterStateContainer> {
@override
Widget build(BuildContext context) {
return Container();
}
}
class FilterStateContainer extends StatefulWidget {
...
static FilterState of(BuildContext context) {
return context
.dependOnInheritedWidgetOfExactType<_FilterInheritedWidget>()!
.state;
}
class FilterState extends State<FilterStateContainer> {
int filterValue = Constants.allFilter;
late SharedPreferences _prefs;
}
import '../constants.dart';
class FilterState extends State<FilterStateContainer> {
...
@override
void initState() {
super.initState();
_loadValue();
}
void _loadValue() {
SharedPreferences.getInstance().then((value) {
_prefs = value;
setState(() {
filterValue = _prefs.getInt(Constants.filterKey) as int;
});
});
}
class FilterState extends State<FilterStateContainer> {
...
void updateFilterValue(int value) {
setState(() {
_prefs.setInt(Constants.filterKey, value);
filterValue = value;
});
}
class _FilterInheritedWidget extends InheritedWidget {
}
class _FilterInheritedWidget extends InheritedWidget {
final FilterState state;
const _FilterInheritedWidget({
Key? key,
required this.state,
required Widget child,
}) : super(key: key, child: child);
class _FilterInheritedWidget extends InheritedWidget {
...
@override
bool updateShouldNotify(_FilterInheritedWidget oldWidget) => true;
class FilterState extends State<FilterStateContainer> {
...
@override
Widget build(BuildContext context) {
return _FilterInheritedWidget(
state: this,
child: widget.child,
);
}