承前一天的查詢方塊功能，透過 SharedPreferences 套件儲存和載入查詢的條件。讓 App開啟時自動載入最後一次的查詢條件。(此機制常用於儲存使用者的登入帳號密碼並自動登入)

daos/shared_preferences_dao.dart

import 'package:shared_preferences/shared_preferences.dart';

class SharedPreferencesDao {
  static SharedPreferences? _prefs;

  static void initialize() async {
    _prefs ??= await SharedPreferences.getInstance();
  } 
  
  static String getSearchKey() {
    String? searchKey;
    if(_prefs != null) {
      searchKey = _prefs!.getString("searchKey");
    }
    searchKey ??= '';

    return searchKey;
  }

  static void setSearchKey(String searchKey) {
    if(_prefs != null) {
    _prefs!.setString("searchKey", searchKey);
    }
  }
}

daos/post_dao.dart

import 'package:webservice_client/models/post.dart';
import 'package:http/http.dart' as http;
import 'package:webservice_client/daos/shared_preferences_dao.dart';
import 'dart:convert';

class PostDao {
  static Future<List<Post>> getPostsAndInitializeSharedPreferences() async {
    SharedPreferencesDao.initialize();

    var url = Uri.parse('https://jsonplaceholder.typicode.com/posts');
    var response = await http.get(url);

    List<Post> posts = (jsonDecode(response.body) as List<dynamic>).map((jsonObject) {
      return Post.fromJson(jsonObject);
    }).toList();

    return posts;
  }
}

components/post_table_with_search.dart

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:webservice_client/daos/shared_preferences_dao.dart';
import 'package:webservice_client/models/post.dart';

// ignore: must_be_immutable
class PostTableWithSearch extends StatefulWidget {
  PostTableWithSearch(this.posts, {super.key});
  List<Post> posts;

  @override
  State createState() {
    return _PostTableWithSearch();
  }
}

class _PostTableWithSearch extends State<PostTableWithSearch> {
  String filterInput = '';
  List<Post> filteredPosts = [];

  void changeFilteredPosts(String userInput) {
    filterInput = userInput;
    filteredPosts = widget.posts.where(
      (element) {
        if(userInput == '') {
          return true;
        }
        else if(element.title.contains(userInput)) {
          //print(element.title);
          return true;
        }
        else {
          return false;
        }
      },
    ).toList();

    if(filteredPosts.isEmpty) {
      filteredPosts.add(Post(0, 0, "查無資料", "查無資料"));
    }

    SharedPreferencesDao.setSearchKey(userInput);
  }

  @override
  void initState() {
    super.initState();

    filterInput = SharedPreferencesDao.getSearchKey();
  }

  @override
  Widget build(BuildContext context) {
    
    if(filteredPosts.isEmpty) {
      changeFilteredPosts(filterInput);
    }

    var searchTextEditingController = TextEditingController()..text = filterInput;

    Widget searchBar = TextField(
      controller: searchTextEditingController,
      decoration: const InputDecoration(
        border: OutlineInputBorder(),
        hintText: 'Enter a search term'
      ),
      onSubmitted: (userInput){
        setState(() {
          changeFilteredPosts(userInput);
        });
      },
    );

    // Convert object variables to data column list
    List<String> columnNames = (jsonDecode(filteredPosts[0].toJsonObjectString()) as Map<String, dynamic>).keys.toList();
    List<DataColumn> dataColumns = columnNames.map((key) {
      return DataColumn(label: Text(key));
    },).toList();

    // Convert object variables to data row list
    List<DataRow> dataRows = filteredPosts.map((post) {
      Map<String, dynamic> postJson = jsonDecode(post.toJsonObjectString()) as Map<String, dynamic>;
      List<DataCell> dataCells = columnNames.map((key){
        return DataCell(
          Text(postJson[key].toString()));
      }).toList();
      
      return DataRow(cells: dataCells);
    },).toList();

    return SingleChildScrollView(
      child: Container(
        alignment: Alignment.topCenter,
        child: Column(children: [
          SizedBox(
            width: 800,
            child: searchBar,
          ),
          SizedBox(
            width: 800,
            child: DataTable(columns: dataColumns, rows: dataRows),
          )
        ]),
      ),
    );
  }       
}

screens/post_screen.dart

import 'package:flutter/material.dart';
import 'package:webservice_client/components/post_table_with_search.dart';
import 'package:webservice_client/daos/post_dao.dart';
import 'package:webservice_client/models/post.dart';

class PostScreen extends StatefulWidget {
  const PostScreen({super.key});



  @override
  State createState() {
    return _PostScreen();
  }
}

class _PostScreen extends State<PostScreen> {
  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: PostDao.getPostsAndInitializeSharedPreferences(), 
      builder: (BuildContext context, AsyncSnapshot<List<Post>> asyncSnapshot) {
        List<Post> posts = [];
        if(asyncSnapshot.connectionState == ConnectionState.done) {
          posts = asyncSnapshot.requireData;

          return Scaffold(
            body: PostTableWithSearch(posts),
          );
        }
        else if(asyncSnapshot.hasError) {
          return const Scaffold(body: Text('Initial data fail!'),);
        }
        else {
          return const Scaffold();
        }
      }
    );
  }
}

pubspec.yaml

name: webservice_client
description: "A http client sample project."
publish_to: 'none'
version: 0.1.0+1

environment:
  sdk: '>=3.2.6 <4.0.0'

dependencies:
  flutter:
    sdk: flutter
  http: ^0.13.4
  shared_preferences: ^2.0.8

dev_dependencies:
  flutter_test:
    sdk: flutter
  flutter_lints: ^2.0.0

flutter:
  uses-material-design: true