selfprivacy.org.app/lib/ui/helpers/widget_size.dart
2023-04-05 13:38:07 +03:00

62 lines
1.5 KiB
Dart

import 'package:flutter/material.dart';
import 'package:flutter/scheduler.dart';
/// A helper widget that calls a callback when its size changes.
///
/// This is useful when you want to know the size of a widget, and use it in
/// another leaf of the tree.
///
/// The [onChange] callback is called after the widget is rendered, and the
/// size of the widget is different from the previous render.
class WidgetSize extends StatefulWidget {
/// Creates a helper widget that calls a callback when its size changes.
const WidgetSize({
required this.onChange,
required this.child,
super.key,
});
/// The child widget, the size of which is to be measured.
final Widget child;
/// The callback to be called when the size of the widget changes.
final Function(Size) onChange;
@override
State<WidgetSize> createState() => _WidgetSizeState();
}
class _WidgetSizeState extends State<WidgetSize> {
@override
Widget build(final BuildContext context) {
SchedulerBinding.instance.addPostFrameCallback(postFrameCallback);
return Container(
key: widgetKey,
child: widget.child,
);
}
var widgetKey = GlobalKey();
Size? oldSize;
void postFrameCallback(final _) {
final context = widgetKey.currentContext;
if (context == null) {
return;
}
final newSize = context.size;
if (newSize == null) {
return;
}
if (oldSize == newSize) {
return;
}
oldSize = newSize;
widget.onChange(newSize);
}
}