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