.tolistasync() ，它在 .net8 maui android 应用程序中可用吗？

Question

在此处输入图像描述我正在开发 .net maui android 应用程序。 我有8000条记录这样的大数据。 一旦客户在 sqlite 数据库中安装应用程序一次，我就会保存数据，然后从数据库中检索以过滤我的数据。 我想等待查询，但我只找到 .tolist() 因为应用程序抛出 null 异常并崩溃。 tolistasync() ，它在 .net8 maui android 应用程序中可用吗？ 或者我如何通过 linq 等待结果？

这是我的数据上下文类代码

    public class DataContext
    {
        private const string DbName = "IdealDiagnosisDb3";
        public static string DbPath = Path.Combine(FileSystem.Current.AppDataDirectory,DbName);
        private SQLiteConnection Database;

        private async Task init()
        {
            //File.Delete(DbPath);

            if (File.Exists(DbPath))
            {
                return;
            }

            Database = new SQLiteConnection(DbPath, SQLiteOpenFlags.Create | SQLiteOpenFlags.ReadWrite | SQLiteOpenFlags.SharedCache);
            
            Database.CreateTable<Drug>();
List<Drug> drugs = new List<Drug>(){big data };

            foreach (Drug drug in drugs)
            {
                Database.Insert(drug);
            }

            Database.CreateTable<TradeDrug>();
List<TradeDrug> TradeDrugs = new List<TradeDrug>(){ big data };
            foreach (TradeDrug TradeDrug in TradeDrugs)
            {
                Database.Insert(TradeDrug);
            }

        }
        public async Task<List<Drug>> LoadAllDrugsAsync()
        {
            init();

            return Database.Table<Drug>().ToList();
        }
        public async Task<List<TradeDrug>> LoadAllTradeDrugsAsync()
        {
            init();

            return Database.Table<TradeDrug>().ToList();

        }

    }

这是我的 HomeViewModel 类代码

    public partial class HomeVM(DataContext dataContext) : BaseVM
    {
        private readonly DataContext _dataContext = dataContext;

        [ObservableProperty]
        private List<Drug> _drugs;

        [ObservableProperty]
        private List<TradeDrug> _tradeDrugs;

        private List<Drug> DrugsWithoutFilter;

        private List<TradeDrug> TradeDrugsWithoutFilter;

        [ObservableProperty]
        private string _searchName;

        [ObservableProperty]
        private string _placeHolderText;

        [ObservableProperty]
        private string _drugName;

        [ObservableProperty]
        private string _diagnosisId;

        [ObservableProperty]
        private string _diagnosisName;

        [ObservableProperty]
        private bool _isDrugSelected;

        [ObservableProperty]
        [NotifyCanExecuteChangedFor(nameof(SearchCommand))]
        private bool _isTradeRadioButtonChecked;

        partial void OnIsTradeRadioButtonCheckedChanged(bool value)
        {
            Search();
        }

        [ObservableProperty]
        private Drug _selectedDrug;

        [ObservableProperty]
        private int _countDrugs;

        public async Task InitializeDrugsAsync() 
        {
            DrugsWithoutFilter = await _dataContext.LoadAllDrugsAsync();

            Drugs = DrugsWithoutFilter;
            CountDrugs =Drugs.Count();
            TradeDrugsWithoutFilter = await _dataContext.LoadAllTradeDrugsAsync();

            TradeDrugs = TradeDrugsWithoutFilter;


            IsDrugSelected = false;
            IsTradeRadioButtonChecked = false;

        }

        [RelayCommand]
        private async Task Search()
        {
            if (!IsTradeRadioButtonChecked)
            {
                PlaceHolderText = "Enter Active Ingredient";

                if (!string.IsNullOrEmpty(SearchName))
                {
                    IsBusy = true;
                    Drugs = DrugsWithoutFilter.Where(x => x.DrugName.ToLower().Contains(SearchName.ToLower())).ToList();

                    CountDrugs = Drugs.Count();
                    IsBusy = false;
                }
                else
                {
                    Drugs = DrugsWithoutFilter;

                    CountDrugs = Drugs.Count();

                }
 
            }
            else
            {
                PlaceHolderText = "Enter Trade Name";

                if (!string.IsNullOrEmpty(SearchName))
                {
                    IsBusy = true;
                    TradeDrugs = TradeDrugsWithoutFilter.Where(x => x.TradeDrugName.ToLower().Contains(SearchName.ToLower())).ToList();

                    CountDrugs = TradeDrugs.Count();
                    IsBusy = false;
                }
                else
                {
                    TradeDrugs = TradeDrugsWithoutFilter;

                    CountDrugs = TradeDrugs.Count();

                }

            }
        }


    

    }

.tolistasync() ，它在 .net8 maui android 应用程序中可用吗？ .

Answer 1

ToListAsync()

是 EntityFramework 包/dll 的一部分。但我在您的代码中没有看到任何

EntityFramework

引用。

但是你可以将代码切换为：

 private void Init() { }

或

 private async Task Init() 
 { 
     // your code here

     // at the end
     await Task.CompletedTask;
 }

或

 private Task Init() 
 { 
     // your code here

     return Task.FromResult(yourResult);
 }