我创建了一个在 sqlite 数据库中存储一些笔记的应用程序。我完成了所有 CRUD 操作并且运行良好，但是当我尝试使用 SearchDelegate 在我的数据库中进行搜索操作时，我遇到了一些问题。在使用 SearchDelegate 进行搜索之前，我会向您展示我的代码

数据库助手:

import 'dart:async';
import 'package:plants/model/plant.dart';
import 'package:sqflite/sqflite.dart';
import 'package:path/path.dart';

class DatabaseHelper {
  static final DatabaseHelper _instance = new DatabaseHelper.internal();

  factory DatabaseHelper() => _instance;

  final String tableNote = 'noteTable';
  final String columnId = 'id';
  final String columnLocation = 'location';
  final String columnTitle = 'title';
  final String columnDescription = 'description';

  static Database _db;

  DatabaseHelper.internal();

  Future<Database> get db async {
    if (_db != null) {
      return _db;
    }
    _db = await initDb();

    return _db;
  }

  initDb() async {
    String databasesPath = await getDatabasesPath();
    String path = join(databasesPath, 'notes.db');

//    await deleteDatabase(path); // just for testing

    var db = await openDatabase(path, version: 1, onCreate: _onCreate);
    return db;
  }

  void _onCreate(Database db, int newVersion) async {
    await db.execute(
        'CREATE TABLE $tableNote($columnId INTEGER PRIMARY KEY,$columnLocation TEXT, $columnTitle TEXT, $columnDescription TEXT)');
  }

  Future<int> saveNote(Note note) async {
    var dbClient = await db;
    var result = await dbClient.insert(tableNote, note.toMap());
//    var result = await dbClient.rawInsert(
//        'INSERT INTO $tableNote ($columnTitle, $columnDescription) VALUES (\'${note.title}\', \'${note.description}\')');

    return result;
  }

  Future<List> getAllNotes() async {
    var dbClient = await db;
    var result = await dbClient.query(tableNote, columns: [columnId, columnLocation , columnTitle, columnDescription]);
//    var result = await dbClient.rawQuery('SELECT * FROM $tableNote');

    return result.toList();
  }

  Future<int> getCount() async {
    var dbClient = await db;
    return Sqflite.firstIntValue(await dbClient.rawQuery('SELECT COUNT(*) FROM $tableNote'));
  }

  Future<Note> getNote(int id) async {
    var dbClient = await db;
    List<Map> result = await dbClient.query(tableNote,
        columns: [columnId, columnLocation , columnTitle, columnDescription],
        where: '$columnId = ?',
        whereArgs: [id]);
//    var result = await dbClient.rawQuery('SELECT * FROM $tableNote WHERE $columnId = $id');

    if (result.length > 0) {
      return new Note.fromMap(result.first);
    }

    return null;
  }

  Future<int> deleteNote(int id) async {
    var dbClient = await db;
    return await dbClient.delete(tableNote, where: '$columnId = ?', whereArgs: [id]);
//    return await dbClient.rawDelete('DELETE FROM $tableNote WHERE $columnId = $id');
  }

  Future<int> updateNote(Note note) async {
    var dbClient = await db;
    return await dbClient.update(tableNote, note.toMap(), where: "$columnId = ?", whereArgs: [note.id]);
//    return await dbClient.rawUpdate(
//        'UPDATE $tableNote SET $columnTitle = \'${note.title}\', $columnDescription = \'${note.description}\' WHERE $columnId = ${note.id}');
  }

  Future close() async {
    var dbClient = await db;
    return dbClient.close();
  }
}

类笔记

class Note {
  int _id;
  String _location;
  String _title;
  String _description;

  Note(this._location,this._title, this._description);

  Note.map(dynamic obj) {
    this._id = obj['id'];
    this._location = obj['location'];
    this._title = obj['title'];
    this._description = obj['description'];
  }

  int get id => _id;
  String get location => _location;
  String get title => _title;
  String get description => _description;

  Map<String, dynamic> toMap() {
    var map = new Map<String, dynamic>();
    if (_id != null) {
      map['id'] = _id;
    }
    map['location'] = _location;
    map['title'] = _title;
    map['description'] = _description;

    return map;
  }

  Note.fromMap(Map<String, dynamic> map) {
    this._id = map['id'];
    this._location = map ['location'];
    this._title = map['title'];
    this._description = map['description'];
  }
}

列表.dart

import 'package:flutter/material.dart';
import 'package:plants/AddPlant.dart';
import 'package:plants/model/plant.dart';
import 'database/dbhelper.dart';

class ListViewNote extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => new ListViewNoteState();
}

class ListViewNoteState extends State<ListViewNote> {
  List<Note> items = new List();
  DatabaseHelper db = new DatabaseHelper();

  @override
  void initState() {
    super.initState();
    db.getAllNotes().then((notes) {
      setState(() {
        notes.forEach((note) {
          items.add(Note.fromMap(note));
        });
      });
    });
  }

  @override
  Widget build(BuildContext context) {  
   return Scaffold(
     appBar: AppBar(
        title: Text('Plant List',
        ),
        centerTitle: true,
        actions: <Widget>[
          IconButton(icon: Icon(Icons.search,
            color: Colors.white,), onPressed: (){
            showSearch(context: context, 
            delegate: DataSearch(this.items));
          })
        ],
      ),
      body: Center(
        child: ListView.builder(
          itemCount: items.length,
          padding: const EdgeInsets.all(15.0),
          itemBuilder: (context, position) {
            return Dismissible(
              background: stackBehindDismiss(),
              key: ObjectKey(items[position]),
              child: Card(
                elevation: 2.0,
                margin: new EdgeInsets.symmetric(horizontal: 0.0,vertical: 2.0),
                child: Column(
                  children: <Widget>[
                    ListTile(
                      title: Text(
                        '${items[position].title}',
                        style: TextStyle(
                          fontSize: 22.0,
                          color: Colors.deepOrangeAccent,
                          ),
                        ),
                        subtitle: Text(
                          '${items[position].description}' + '' + '${items[position].location}',
                          style: new TextStyle(
                            fontSize: 18.0,
                            fontStyle: FontStyle.italic,
                            ),
                          ), 
                          onTap: () => _navigateToNote(context, items[position]),
                      ),
                    ],
                  ),
                ),
                onDismissed: (dirction){
                  var item = items.elementAt(position);
                  _deleteNote(context, items[position], position);
                  Scaffold.of(context).showSnackBar(SnackBar(
                    content: Text("Item deleted"),
                    ));
                  },
              );
            }
         ),
         ),
         floatingActionButton: FloatingActionButton(
           backgroundColor: Colors.green[700],
           child: Icon(Icons.add),
           onPressed: () => _createNewNote(context),
          ),
      );
    }
    void _deleteNote(BuildContext context, Note note, int position) async {
      db.deleteNote(note.id).then((notes) {
       setState(() {
         items.removeAt(position);
         });
        });
      }
    void _navigateToNote(BuildContext context, Note note) async {
      String result = await Navigator.push(
        context,MaterialPageRoute(builder: (context) => NoteScreen(note)),
        );
        if (result == 'update') {
          db.getAllNotes().then((notes) {
            setState(() {
              items.clear();
              notes.forEach((note) {
                items.add(Note.fromMap(note));
                });
              });
            });
          }
        }
    void _createNewNote(BuildContext context) async {
      String result = await Navigator.push(
        context,MaterialPageRoute(builder: (context) => NoteScreen(Note('', '', ''))),
        );
        if (result == 'save') {
          db.getAllNotes().then((notes) {
            setState(() {
              items.clear();
              notes.forEach((note) {
                items.add(Note.fromMap(note));
                });
              });
            });
          }
        }
     stackBehindDismiss() {
       return Container(
         alignment: Alignment.centerRight,
         padding: EdgeInsets.only(right: 20.0),
         color: Colors.green[700],
         child: Icon(
           Icons.delete,
           color: Colors.white,
          ),
        );
       }                
 }

class DataSearch extends SearchDelegate<Note> {
  DatabaseHelper db = new DatabaseHelper();
  final List<Note> items = new List();
  List<Note> suggestion = new List();
  // ListViewNoteState i = ListViewNoteState();

   DataSearch(this.suggestion);

  @override
  ThemeData appBarTheme(BuildContext context) {
    assert(context != null);
    final ThemeData theme = Theme.of(context);
    assert(theme != null);
    return theme;
  }

  @override
  List<Widget> buildActions(BuildContext context) {
    return [
      IconButton(icon: Icon(Icons.clear), onPressed: () {
        query = '';
      } )
    ];
  }

  @override
  Widget buildLeading(BuildContext context) {
    return IconButton(
      icon: AnimatedIcon(
        icon: AnimatedIcons.menu_arrow,
        progress: transitionAnimation,
      ),
      onPressed: (){
        close(context, null);
      },
    );
  }

  @override
  Widget buildResults(BuildContext context) { 
  }

  @override
  Widget buildSuggestions(BuildContext context) {
    final suggestion = query.isEmpty 
    ? items 
    : items.where((target) => target.title.startsWith(query)).toList(); 
    if(items.isEmpty)
    {
      print("Null");
    }
    return ListView.builder(
      itemBuilder: (context, position)=>
          ListTile(
            title: Text(items[position].title),
          ),
      itemCount: suggestion.length,
    );
  }
}

在 CRUD 上，一切正常，我添加了 3 条记录，但是当我使用 SearchDelegate 实现搜索时，我没有得到任何结果。

我需要的是使用搜索栏从数据库中搜索列表

最佳答案

试试这个:

return ListView.builder(
  itemBuilder: (context, index)=>
      ListTile(
        title: Text(suggestion[index].title),
      ),

它应该可以工作并显示正确的结果，至少我的是这样工作的，但我认为当您构建结果或点击打开它或类似的东西时，您必须指向项目列表。

关于flutter - 如何用sqflite flutter实现search delegate，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/56286923/