87 lines
2.3 KiB
Dart
87 lines
2.3 KiB
Dart
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import 'package:flutter/material.dart';
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/// loadLibrary
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typedef LoadLibraryBuilder = Future<dynamic> Function();
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/// deferredWidgetBuilder
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typedef DeferredWidgetBuilder = Widget Function();
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/// 延迟加载组件
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/// 不在 build 里使用 FutureBuilder 加载，因为 build 执行多少次就会导致 widget 创建多少次
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/// 这里在 initState 加载，或者当 DeferredWidgetBuilder 改变时重新加载
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class DeferredWidget extends StatefulWidget {
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const DeferredWidget({
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Key? key,
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required this.loadLibrary,
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required this.builder,
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Widget? placeholder,
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}) : placeholder = placeholder ?? const DeferredLoading(),
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super(key: key);
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final LoadLibraryBuilder loadLibrary;
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final DeferredWidgetBuilder builder;
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final Widget placeholder;
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static final Map<LoadLibraryBuilder, Future<dynamic>> _moduleLoaders = {};
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static final Set<LoadLibraryBuilder> _loadedModules = {};
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/// 预加载
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static Future<dynamic> preload(LoadLibraryBuilder loadLibrary) {
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if (!_moduleLoaders.containsKey(loadLibrary)) {
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_moduleLoaders[loadLibrary] = loadLibrary().then((_) {
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_loadedModules.add(loadLibrary);
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});
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}
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return _moduleLoaders[loadLibrary]!;
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}
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@override
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State<DeferredWidget> createState() => _DeferredWidgetState();
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}
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class _DeferredWidgetState extends State<DeferredWidget> {
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Widget? _loadChild;
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DeferredWidgetBuilder? _loadBuilder;
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@override
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void initState() {
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super.initState();
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if (DeferredWidget._moduleLoaders.containsKey(widget.loadLibrary)) {
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_onLibraryLoaded();
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} else {
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DeferredWidget.preload(widget.loadLibrary)
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.then((_) => _onLibraryLoaded());
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}
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}
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void _onLibraryLoaded() {
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setState(() {
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_loadBuilder = widget.builder;
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_loadChild = _loadBuilder?.call();
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});
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}
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@override
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Widget build(BuildContext context) {
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if (_loadBuilder != widget.builder && _loadChild != null) {
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_loadBuilder = widget.builder;
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_loadChild = _loadBuilder?.call();
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}
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return _loadChild ?? widget.placeholder;
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}
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}
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/// 延迟加载Loading
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class DeferredLoading extends StatelessWidget {
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const DeferredLoading({Key? key}) : super(key: key);
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@override
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Widget build(BuildContext context) {
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return Container(
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color: Colors.white,
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alignment: Alignment.center,
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child: const CircularProgressIndicator(),
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);
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}
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}
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