Question

我正在使用 streams 通过 streamBuilder 显示我的数据。问题是信息流给了我未来<列表> 快照，我需要使用 length 作为 itemCount 。 / p>

也使用 sqflite ，我从没见过两者的例子。

下面是我的代码；

import 'package:flutter/material.dart';
import 'package:password_safe/blocs/safe_card_bloc.dart';
import 'package:password_safe/models/SafeCard.dart';

class Body extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
      initialData: safeCardBloc.getCards(),
      stream: safeCardBloc.getStream,
      builder: (context, snapshot) {
        return snapshot.hasError
            ? Center(
                child: Text(snapshot.error.toString()),
              )
            : snapshot.hasData
                ? buildSafeCardListItems(snapshot)
                : Center(
                    child: Text("Veri yok"),
                  );
      },
    );
  }

  buildSafeCardListItems(AsyncSnapshot snapshot) {
    return ListView.builder(
      itemCount: snapshot.data.length, // problem
      itemBuilder: (context, index) {
        List<SafeCard> safeCards = snapshot.data;
        return Padding(
          padding: EdgeInsets.only(top: 8),
          child: Card(
            margin: EdgeInsets.fromLTRB(20, 6, 20, 0),
            child: ListTile(
              title: Text(
                "Name:  ${safeCards[index].name}",
                style: TextStyle(
                  fontWeight: FontWeight.w600,
                ),
              ),
              subtitle: Text(
                "Password:  ${safeCards[index].password}",
                style: TextStyle(
                  fontWeight: FontWeight.w600,
                ),
              ),
            ),
          ),
        );
      },
    );
  }
}

类'Future >'没有实例获取器'length'。接收方：“ Future >”的实例尝试致电：长度

import 'dart:async';

import 'package:password_safe/data/db_helper.dart';
import 'package:password_safe/models/SafeCard.dart';

class SafeCardBloc {
  final safeCardStreamController = StreamController.broadcast();

  Stream get getStream => safeCardStreamController.stream;
  final dbHelper = DbHelper();

  void addToSafe(SafeCard card) async {
    dbHelper.insert(card);
    safeCardStreamController.sink.add(dbHelper.getSafeCards());
  }

   Future<List<SafeCard>> getCards() async {
    var cards = dbHelper.getSafeCards();
    print(cards);
    return cards;
  }
}

final safeCardBloc = SafeCardBloc();

数据库类

import 'dart:async';

import 'package:password_safe/models/SafeCard.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';

class DbHelper {
  Database _db;

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

  Future<Database> initializeDb() async {
    String dbPath = join(await getDatabasesPath(), "safeCardDb.db");
    var safeCardDb = openDatabase(dbPath, version: 1, onCreate: createDb);
    return safeCardDb;
  }

  void createDb(Database db, int version) async {
    await db.execute(
        "Create table safeCards(id integer primary key autoincrement, name text, description text, password text)");
  }

  Future<List<SafeCard>> getSafeCards() async {
    Database db = await this.db;
    var result = await db.query("safeCards");
    return List.generate(result.length, (i) {
      return SafeCard.fromObject(result[i]);
    });
  }

  Future<int> insert(SafeCard safeCard) async {
    Database db = await this.db;
    var result = await db.insert("safeCards", safeCard.toMap());
    return result;
  }

  Future<int> delete(int id) async {
    Database db = await this.db;
    var result = await db.rawDelete("delete from safeCards where id= $id");
    return result;
  }

  Future<int> update(SafeCard safeCard) async {
    Database db = await this.db;
    var result = await db.update("safeCards", safeCard.toMap(),
        where: "id=?", whereArgs: [safeCard.id]);
    return result;
  }
}

Answer 1

我认为“ snapshot.data”不是列表。所以，

来自

buildSafeCardListItems(AsyncSnapshot snapshot) {
  return ListView.builder(
    itemCount: snapshot.data.length, // problem
    itemBuilder: (context, index) {
      List<SafeCard> safeCards = snapshot.data;

到

buildSafeCardListItems(AsyncSnapshot snapshot) {
  List<SafeCard> safeCards = snapshot.data;
  return ListView.builder(
    itemCount: safeCards.length,
    itemBuilder: (context, index) {

类Future <List <Object >>没有实例获取方法长度

1 个答案: