import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';
typedef OnWidgetSizeChange = void Function(Size size);
class MeasuredSize extends StatefulWidget {
final Widget child;
final OnWidgetSizeChange onChange;
const MeasuredSize({
Key? key,
required this.onChange,
required this.child,
}) : super(key: key);
@override
_MeasuredSizeState createState() => _MeasuredSizeState();
}
class _MeasuredSizeState extends State<MeasuredSize> {
bool _calculating = true;
@override
void initState() {
SchedulerBinding.instance!.addPostFrameCallback(postFrameCallback);
super.initState();
}
@override
Widget build(BuildContext context) {
SchedulerBinding.instance!.addPostFrameCallback(postFrameCallback);
return AnimatedOpacity(
duration: const Duration(milliseconds: 100),
opacity: _calculating ? 0.0 : 1.0,
child: Container(
key: widgetKey,
child: widget.child,
),
);
}
var widgetKey = GlobalKey();
Size? oldSize;
void postFrameCallback(_) {
_calculating = true;
var context = widgetKey.currentContext!;
Size newSize = context.size!;
_calculating = false;
if (newSize == Size.zero) return;
if (oldSize == newSize) return;
oldSize = newSize;
widget.onChange(newSize);
}
}