Flutter SQFLite 如何将 Future List db 值读入 Text Widget 变量

Question

我的目标是使用 Future 函数从数据库中提取单个值，并在文本小部件中显示该值，如下所示：Widget myFlag = Text(myvar);

我的代码解释：

final String myTable = 'myFlag';

// the PhilaFields and myPhila Classes are part of the model class.
class PhilaFields {
  static final List<String> values = [id, myFlag];
  static final String id = '_id'; // SQL convention
  static final String myFlag = 'isFlag';
}

class myPhila {
  late final int? id;
  late int isFlag=0;
  myPhila({required this.id,required this.isFlag});
  myPhila copy({int? id,int? isFlag}) => myPhila(id: id ?? this.id,isFlag: isFlag ?? this.isFlag);
  Map<String, Object?> toJson() => {if (id != null) PhilaFields.id: id,PhilaFields.myFlag: isFlag};
  static myPhila fromJson(Map<String, Object?> json) => myPhila(id: json[PhilaFields.id] as int?,isFlag: json[{PhilaFields.myFlag}] as int);
}

//This function is doing DB rawquery to extract a list of values form myTable
//The following code extracts the List of values.
Future<List<myPhila>> read_isFlag() async {
    final db = await instance.dataBase;
    final result = await db.rawQuery('SELECT isFlag FROM $myTable');
    final list = result.map((json) => myPhila.fromJson(json)).toList();
    if(list.isNotEmpty) return list; else throw Exception('Empty List');
}

//Here I need to convert Future function result into a single String variable
//This is Future function returning Future List which I don't know how to convert to a 
//single String value:
Future readFlag() async {
    List xp=[];
    late String str;
    await DBHelper.instance.read_isFlag().then((xp) {
      str = xp.toString();
      return str;
    });
}

我的最终目标：我需要在 UI 文本小部件中显示单个值：

小部件 myFlag = Text(myvar);

我不知道如何使用 Future 函数来获取 db 值。

请帮忙。谢谢

Answer 1

你可以试试这个代码片段，它基本上做了同样的事情，但在访问值时略有不同，如果 read_isFlag() 返回一个列表，它将访问列表的第一个值你可以通过这样做获得单个值这个。

Future<String> readFlag() async {
  final flagList = await DBHelper.instance.read_isFlag();
  if (flagList.isNotEmpty) {
    return flagList[0].isFlag.toString();
  } else {
    throw Exception('Empty List');
  }
}