dab246
73 lines
2.2 KiB
Dart
73 lines
2.2 KiB
Dart
import 'dart:async';
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import 'package:flutter/material.dart';
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typedef LibraryLoader = Future<void> Function();
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typedef DeferredWidgetBuilder = Widget Function();
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/// Wraps the child inside a deferred module loader.
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///
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/// The child is created and a single instance of the Widget is maintained in
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/// state as long as closure to create widget stays the same.
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///
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class DeferredWidget extends StatefulWidget {
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DeferredWidget(
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this.libraryLoader,
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this.createWidget,
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{Key? key, Widget? placeholder}
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) : placeholder = placeholder ?? Container(), super(key: key);
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final LibraryLoader libraryLoader;
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final DeferredWidgetBuilder createWidget;
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final Widget placeholder;
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static final Map<LibraryLoader, Future<void>> _moduleLoaders = {};
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static final Set<LibraryLoader> _loadedModules = {};
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static Future<void> preload(LibraryLoader loader) {
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if (!_moduleLoaders.containsKey(loader)) {
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_moduleLoaders[loader] = loader().then((dynamic _) {
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_loadedModules.add(loader);
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});
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}
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return _moduleLoaders[loader]!;
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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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_DeferredWidgetState();
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Widget? _loadedChild;
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DeferredWidgetBuilder? _loadedCreator;
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@override
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void initState() {
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/// If module was already loaded immediately create widget instead of
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/// waiting for future or zone turn.
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if (DeferredWidget._loadedModules.contains(widget.libraryLoader)) {
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_onLibraryLoaded();
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} else {
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DeferredWidget.preload(widget.libraryLoader).then((dynamic _) => _onLibraryLoaded());
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}
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super.initState();
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}
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void _onLibraryLoaded() {
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setState(() {
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_loadedCreator = widget.createWidget;
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_loadedChild = _loadedCreator!();
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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 closure to create widget changed, create new instance, otherwise
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/// treat as const Widget.
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if (_loadedCreator != widget.createWidget && _loadedCreator != null) {
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_loadedCreator = widget.createWidget;
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_loadedChild = _loadedCreator!();
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}
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return _loadedChild ?? widget.placeholder;
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}
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} |