custom_search_delgates.dart
import 'package:flutter/material.dart';typedef onSearchChanged = Future<List<String>> Function(String);class SearchWithSuggestionDelegate extends SearchDelegate<String> { ///[onSearchChanged] gets the [query] as an argument. Then this callback ///should process [query] then return an [List<String>] as suggestions. ///Since its returns a [Future] you get suggestions from server too. final onSearchChanged onSearchChanged; ///This [_oldFilters] used to store the previous suggestions. While waiting ///for [onSearchChanged] to completed, [_oldFilters] are displayed. List<String> _oldFilters = const []; SearchWithSuggestionDelegate({String searchFieldLabel, this.onSearchChanged}) : super(searchFieldLabel: searchFieldLabel); /// @override Widget buildLeading(BuildContext context) { return IconButton( icon: const Icon(Icons.arrow_back), onPressed: () => Navigator.pop(context), ); } @override List<Widget> buildActions(BuildContext context) { return [ IconButton( icon: Icon(Icons.clear), onPressed: () => query = "", ), ]; } ///onSubmit in the keyboard, returns the [query] @override void showResults(BuildContext context) { close(context, query); } ///Since [showResults] is overridden we can don't have to build the results. @override Widget buildResults(BuildContext context) => null; @override Widget buildSuggestions(BuildContext context) { return FutureBuilder<List<String>>( future: onSearchChanged != null ? onSearchChanged(query) : null, builder: (context, snapshot) { if (snapshot.hasData) _oldFilters = snapshot.data; return ListView.builder( itemCount: _oldFilters.length, itemBuilder: (context, index) { return ListTile( leading: Icon(Icons.restore), title: Text("${_oldFilters[index]}"), onTap: () => close(context, _oldFilters[index]), ); }, ); }, ); }}用法：
import 'package:flutter/material.dart';import 'package:flutter_app/custom_search_delgates.dart';import 'package:shared_preferences/shared_preferences.dart';void main() { runApp(MaterialApp(home: Home()));}class Home extends StatefulWidget { @override _HomeState createState() => _HomeState();}class _HomeState extends State<Home> { Future<void> _showSearch() async { final searchText = await showSearch<String>( context: context, delegate: SearchWithSuggestionDelegate( onSearchChanged: _getRecentSearchesLike, ), ); //Save the searchText to SharedPref so that next time you can use them as recent searches. await _saveToRecentSearches(searchText); //Do something with searchText. Note: This is not a result. } Future<List<String>> _getRecentSearchesLike(String query) async { final pref = await SharedPreferences.getInstance(); final allSearches = pref.getStringList("recentSearches"); return allSearches.where((search) => search.startsWith(query)).toList(); } Future<void> _saveToRecentSearches(String searchText) async { if (searchText == null) return; //Should not be null final pref = await SharedPreferences.getInstance(); //Use `Set` to avoid duplication of recentSearches Set<String> allSearches = pref.getStringList("recentSearches")?.toSet() ?? {}; //Place it at first in the set allSearches = {searchText, ...allSearches}; pref.setStringList("recentSearches", allSearches.toList()); } @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar( title: Text("Search Demo"), actions: <Widget>[ IconButton( icon: Icon(Icons.search), onPressed: _showSearch, ), ], ), ); }}
