我有一个carouselview，在那个视图中我有一个ObservableCollection绑定为itemssource，我可以绑定这个集合，当我在OnAppearing事件中执行视图模型的命令时，它会显示出来。
有效的代码：

• • 第二页**

public partial class SecondPage : ContentPage
{

     public Coll(bool hard, string subject)
     {
            InitializeComponent();
            var vm = (DataSelectionViewModel)BindingContext;

            vm.Hard = hard;
            vm.Subject = subject;
            /* had to set "hard" and "subject" here again, otherwise data won't load */
     }

     protected override async void OnAppearing()
     {
         var vm = (DataSelectionViewModel)BindingContext;
         base.OnAppearing();
         await vm.LoadData.ExecuteAsync().ConfigureAwait(false);
     }
}

• • 第二页的视图模型**

public class DataSelectionViewModel : BaseViewModel
{
   private string subject;
   public string Subject { get => subject; set => SetProperty(ref subject, value); }

   private bool hard;
   public bool Hard { get => hard; set => SetProperty(ref hard, value); }

   public ObservableCollection<Items> FilteredData { get; set; }

   public UserSelectionViewModel()
   {
            _dataStore = DependencyService.Get<IDataStore>();

            LoadData= new AsyncAwaitBestPractices.MVVM.AsyncCommand(FilterData);

            FilteredData = new ObservableCollection<Items>();
   }
   public async Task FilterData()
   {
            FilteredData.Clear();
            var filtereddata = await _dataStore.SearchData(Hard, Subject).ConfigureAwait(false);
            foreach (var data in filtereddata)
            { 
                FilteredData.Add(data);
            }
   }  
}

• • 第一页，其中第二页获取"困难"和"主题"值**

private async void ButtonClick(object sender, EventArgs e)
{
   var vm = (BaseViewModel)BindingContext;

   vm.Hard = HardButtonSelected == Hard;
   vm.Subject = vm.Subject.ToLower();

   await Navigation.PushAsync(new SecondPage(vm.Hard, vm.Subject));
   
}

所以我想修改我的代码，这样如果我按下第一页上的按钮，数据就会立即开始过滤并添加到ObservableCollection中，完成后，导航到第二页，但是如果我尝试将其加载到BaseViewModel中，然后从第二个视图模型中获取数据，它不会显示数据。
无法工作的代码：

• • 第二页**

public partial class SecondPage : ContentPage
{

     public SecondPage()
     {
            InitializeComponent();
     }
}

• • 第二页的视图模型**

public class DataSelectionViewModel : BaseViewModel
{

   public ObservableCollection<Items> FilteredData { get; set; }

   public UserSelectionViewModel()
   {

            FilteredData = new ObservableCollection<Items>();
   }
}

• • 基本视图模型**

public class BaseViewModel : INotifyPropertyChanged
{
   private string subject;
   public string Subject { get => subject; set => SetProperty(ref subject, value); }

   private bool hard;
   public bool Hard { get => hard; set => SetProperty(ref hard, value); }

   public ObservableCollection<Items> FilteredData { get; set; }

   /* BaseViewModel has implementation of SetProperty */
}

• • 第一页，其中第二页获取"困难"和"主题"值**

private async void ButtonClick(object sender, EventArgs e)
{
   var vm = (BaseViewModel)BindingContext;

   vm.Hard = HardButtonSelected == Hard;
   vm.Subject = vm.Subject.ToLower();
}

• • 首页视图模型**

public class FirstPageViewModel : BaseViewModel
    {

        public IAsyncCommand MehetButtonClickedCommand { get; }
        readonly IPageService pageService;
        readonly IFeladatokStore _feladatokStore;
        public FeladatValasztoViewModel()
        {
            _dataStore = DependencyService.Get<IDataStore>();
            ButtonClickedCommand = new AsyncCommand(ButtonClicked);

            pageService = DependencyService.Get<IPageService>();
        }

        private async Task ButtonClicked()
        {
            await FilterData();

            await pageService.PushAsync(new SecondPage());
        }

        private async Task FilterData()
        {
            FilteredData.Clear();
            var datas = await _dataStore.SearchData(Subject, Hard).ConfigureAwait(false);
            foreach (var data in datas)
            {
                FilteredData.Add(data);
            }
        }

基本上这会产生一个null异常错误，我也试过把ObservableCollection作为SecondPage（ObservableCollection x）的一个参数，这确实起作用了，但是因为我必须为它创建另一个ObservableCollection，并从一个复制到另一个，它停止了异步，并冻结了几秒钟，所以我的问题是，我怎么才能让它异步呢？