53 lines
1.5 KiB
Dart
53 lines
1.5 KiB
Dart
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import 'package:flutter/material.dart';
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/// A lazy-loading [IndexedStack] that loads [children] accordingly.
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class LazyIndexedStack extends StatefulWidget {
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const LazyIndexedStack({
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Key? key,
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this.alignment = AlignmentDirectional.topStart,
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this.textDirection,
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this.sizing = StackFit.loose,
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this.index = 0,
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this.children = const [],
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}) : super(key: key);
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final AlignmentGeometry alignment;
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final TextDirection? textDirection;
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final StackFit sizing;
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final int index;
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final List<Widget> children;
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@override
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LazyIndexedStackState createState() => LazyIndexedStackState();
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}
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class LazyIndexedStackState extends State<LazyIndexedStack> {
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late List<bool> _activated = _initializeActivatedList();
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List<bool> _initializeActivatedList() => List<bool>.generate(widget.children.length, (i) => i == widget.index);
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@override
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void didUpdateWidget(covariant LazyIndexedStack oldWidget) {
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if (oldWidget.children.length != widget.children.length) {
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_activated = _initializeActivatedList();
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}
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super.didUpdateWidget(oldWidget);
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}
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@override
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Widget build(BuildContext context) {
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// Mark current index as active
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_activated[widget.index] = true;
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final children = List.generate(_activated.length, (i) {
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return _activated[i] ? widget.children[i] : const SizedBox.shrink();
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});
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return IndexedStack(
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alignment: widget.alignment,
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sizing: widget.sizing,
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textDirection: widget.textDirection,
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index: widget.index,
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children: children,
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);
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}
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}
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