Question

我正在使用 SQFLite 将数据存储在flutter应用程序中。数据库提供者是

class MessageDatabaseProvider {
  Database db;

  Future open() async {
    final path = join(await getDatabasesPath(), databaseName);
    db = await openDatabase(
        path,
        version: 1,
        onCreate: (Database db, int version) async {
          await db.execute('''
            create table $tableMessage (
              $columnId integer primary key autoincrement,
              $columnCountryCode text not null,
              $columnPhoneNumber text not null,
              $columnMessage text null,
              $columnCreated integer null)
            ''');
        }
    );
  }

  Future<List<Message>> list() async {
    List<Map> maps = await db.query(tableMessage,
      columns: [columnId, columnCountryCode, columnPhoneNumber, columnMessage, columnCreated],
      orderBy: columnId
    );

    List<Message> list = [];
    maps.forEach((element) {
      list.add(Message.fromMap(element));
    });

    return list;
  }
}

并构建一个 ListView

class _MessageHistoryListState extends State<MessageHistoryList> {
  final _database = MessageDatabaseProvider();

  @override
  Widget build(BuildContext context) {
    return Center(
      child: _buildMessageHistory(),
    );
  }
  
  Widget _buildMessageHistory() {

    _database.open();
    
    return FutureBuilder<List>(
      future: _getList(),
      initialData: [],
      builder: (context, snapshot) {
        print(snapshot);
        return snapshot.hasData ?
          ListView.builder(
            padding: EdgeInsets.all(16.0),
            itemCount: snapshot.data.length,
            itemBuilder: (context, i) {
              return _buildRow(snapshot.data[i]);
            },
          )
        : Center(
          child: CircularProgressIndicator(),
        );
      },
    );
  }
}

它第一次显示项目列表，然后在更改导航后出现错误

AsyncSnapshot<List<dynamic>>(ConnectionState.done, null, NoSuchMethodError: The method 'query' was called on null.

Answer 1

在使用以下行将其关闭之前，您无法使用openDatabase

await db.close();

如果不重新创建窗口小部件，则应从 _database.open();调用init()。从_database.open();

中删除_buildMessageHistory()

Flutter FutureBuilder等待SQFLite中的数据库连接

1 个答案: