C# 除非重新加载UI HotReload，否则Xamarin.Forms SwipeView CommandParameter为null

好的，我有一个CollectionView绑定到一个“Show”对象的集合。这个集合视图有相当多的内容。我有一个命令，用于当用户选择一个节目（单点击重定向到详细信息页面）、选择多个项目以执行多项目删除，以及滑动以对每个单独的节目执行基本发布功能。除了刷卡以外，一切都正常。出于某种原因，当启动其中一个滑动命令时，传递给该命令的“Show”对象为null。但是，我已经为此启用了热重新加载，如果我所做的只是保存xaml文件，它就可以正常工作。传递的显示不是空的，它可以像我期望的那样工作。当我保存xaml文件时，我甚至不需要更改任何内容，我只是简单地保存，没有新的更改（ctrl+s），代码开始工作，我的滑动项命令也很好。以下是我的代码参考：

xaml：

视图模型：

public class ShowsViewModel : BaseViewModel
    {
        public ObservableCollection<Show> Shows { get; }
        public ObservableCollection<object> SelectedShows { get; }

        public Command SelectionChangedCommand { get; }
        public Command ShowSelectedCommand { get; }
        public Command DeleteMultipleShowsCommand { get; }
        public Command AddShowCommand { get; }
        public Command LoadShowsCommand { get; }
        public Command SwipeIsPublishCommand { get; }
        public Command SwipeIsActiveCommand { get; }
        public Command SwipeIsSoldOutCommand { get; }

        public ShowsViewModel()
        {
            Title = "Shows";
            Shows = new ObservableCollection<Show>();
            SelectedShows = new ObservableCollection<object>();

            LoadShowsCommand = new Command(async () => await LoadItems());
            AddShowCommand = new Command(OnAddItem);
            ShowSelectedCommand = new Command<Show>(OnItemSelected);
            DeleteMultipleShowsCommand = new Command(async () => await DeleteShows(), () => CanDeleteShows());
            SelectionChangedCommand = new Command(DeleteMultipleShowsCommand.ChangeCanExecute);

            SwipeIsPublishCommand = new Command<Show>(async (show) => await PublishShow(show));
            SwipeIsActiveCommand = new Command<Show>(async (show) => await ActivateShow(show));
            SwipeIsSoldOutCommand = new Command<Show>(async (show) => await SoldOutShow(show));
        }

        private async Task LoadItems()
        {
            IsBusy = true;

            try
            {
                Shows.Clear();
                var shows = await DataService.Shows.GetItemsAsync();
                foreach (var show in shows)
                {
                    this.Shows.Add(show);
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex);
            }
            finally
            {
                IsBusy = false;
            }
        }

        public void OnAppearing()
        {
            IsBusy = true;
        }

        private async void OnAddItem(object obj)
        {
            await Shell.Current.GoToAsync(nameof(CreateShowPage));
        }

        private async void OnItemSelected(Show show)
        {
            if (show == null)
                return;

            // This will push the ItemDetailPage onto the navigation stack
            await Shell.Current.GoToAsync($"{nameof(ShowDetailPage)}?{nameof(ShowDetailViewModel.ShowId)}={show.ShowId}");
        }

        private bool CanDeleteShows()
        {
            return SelectedShows.Count() > 0;
        }

        private async Task DeleteShows()
        {
            if (SelectedShows != null && SelectedShows.Count() > 0)
            {
                bool confirm = await App.Current.MainPage.DisplayAlert("Delete?", $"Are you sure you want to delete the selected show(s)?", "Yes", "No");
                if (confirm)
                {
                    IsBusy = true;

                    var totalDeleted = 0;
                    foreach (var showobj in SelectedShows)
                    {
                        var show = (Show)showobj;
                        var response = await DataService.Shows.DeleteItemAsync(show.ShowId.ToString());
                        if (response)
                        {
                            totalDeleted++;
                        }
                    }

                    await App.Current.MainPage.DisplayAlert("Delete Results", $"Deleted {totalDeleted} show(s).", "Ok");

                    // This will reload the page
                    IsBusy = true;
                }
            }
        }

        private async Task PublishShow(Show show)
        {
            if (show != null)
            {
                show.IsPublished = !show.IsPublished;
                await DataService.Shows.UpdateItemAsync(show);

                var message = show.IsPublished ? "published" : "unpublished";
                await App.Current.MainPage.DisplayAlert($"Show Updated!", $"Show: {show.ShowTitle} has been {message}", "Ok");
            }
        }

        private async Task ActivateShow(Show show)
        {
            if (show != null)
            {
                show.IsActive = !show.IsActive;
                await DataService.Shows.UpdateItemAsync(show);

                var message = show.IsActive ? "activated" : "archived";
                await App.Current.MainPage.DisplayAlert($"Show Updated!", $"Show: {show.ShowTitle} has been {message}", "Ok");
            }
        }

        private async Task SoldOutShow(Show show)
        {
            if (show != null)
            {
                show.IsSoldOut = !show.IsSoldOut;
                await DataService.Shows.UpdateItemAsync(show);

                var message = show.IsSoldOut ? "sold out" : "not sold out";
                await App.Current.MainPage.DisplayAlert($"Show Updated!", $"Show: {show.ShowTitle} has been marked as {message}", "Ok");
            }
        }
    }

public类ShowsViewModel:BaseViewModel
{
公共observeCollection显示{get；}
公共ObservableCollection Selected显示{get；}
公共命令SelectionChangedCommand{get；}
公共命令ShowSelectedCommand{get；}
公共命令DeleteMultipleShowsCommand{get；}
公共命令AddShowCommand{get；}
公共命令LoadShowsCommand{get；}
公共命令SwipeIsPublishCommand{get；}
公共命令SwipeIsActiveCommand{get；}
公共命令SwipeIsSoldOutCommand{get；}
公共ShowsViewModel（）
{
Title=“显示”；
Shows=新的ObservableCollection（）；
SelectedShows=新的ObservableCollection（）；
LoadShowsCommand=new命令（async（）=>await LoadItems（））；
AddShowCommand=新命令（OnAddItem）；
ShowSelectedCommand=新命令（已选择）；
DeleteMultipleShowCommand=new命令（异步（）=>await DeleteShows（），（）=>CanDeleteShows（））；
SelectionChangedCommand=new命令（DeleteMultipleShowCommand.ChangeCanExecute）；
SwipeIsPublishCommand=新命令（异步（显示）=>Wait PublishShow（显示））；
SwipeIsActiveCommand=new命令（异步（显示）=>wait-ActivateShow（显示））；
SwipeIsSoldOutCommand=新命令（异步（显示）=>wait SoldOutShow（显示））；
}
专用异步任务LoadItems（）
{
IsBusy=true；
尝试
{
Shows.Clear（）；
var shows=await DataService.shows.GetItemsAsync（）；
foreach（在显示中显示变量）
{
this.Shows.Add（show）；
}
}
捕获（例外情况除外）
{
Debug.WriteLine（ex）；
}
最后
{
IsBusy=false；
}
}
公开无效
{
IsBusy=true；
}
专用异步无效OnAddItem（对象obj）
{
wait Shell.Current.GoToAsync（name of（CreateShowPage））；
}
已选择专用异步无效（显示）
{
if（show==null）
返回；
//这将把ItemDetailPage推送到导航堆栈上
wait Shell.Current.GoToAsync（$“{nameof（showtailPage）}？{nameof（showtailviewmodel.ShowId）}={show.ShowId}”）；
}
二等兵布尔·坎德莱斯豪斯（）
{
返回SelectedShows.Count（）>0；
}
专用异步任务DeleteShows（）
{
if（SelectedShows！=null&&SelectedShows.Count（）>0）
{
bool confirm=wait App.Current.MainPage.DisplayAlert（“删除？”，$”是否确实要删除所选节目？”，“是”，“否”）；
如果（确认）
{
IsBusy=true；
var totalDeleted=0；
foreach（在SelectedShows中的var showobj）
{
var show=（show）showobj；
var response=await DataService.Shows.DeleteItemAsync（show.ShowId.ToString（））；
如果（答复）
{
全部删除++；
}
}
等待App.Current.MainPage.DisplayAlert（“删除结果“，$”已删除{totalDeleted}显示“，”确定”）；
//这将重新加载页面
IsBusy=true；
}
}
}
专用异步任务PublishShow（Show Show）
{
如果（显示！=null）
{
show.IsPublished=！show.IsPublished；
等待DataService.Shows.UpdateItemAsync（show）；
var message=show.IsPublished？“published”：“unpublished”；
等待App.Current.MainPage.DisplayAlert（$“显示已更新！”，$“显示：{Show.ShowTitle}已被{message}”，“确定”）；
}
}
专用异步任务ActivateShow（显示）
{
如果（显示！=null）
{
show.IsActive=！show.IsActive；
等待DataService.Shows.UpdateItemAsync（show）；
var message=show.IsActive？“已激活”：“已存档”；
等待App.Current.MainPage.DisplayAlert（$“显示已更新！”，$“显示：{Show.ShowTitle}已被{message}”，“确定”）；
}
}
专用异步任务SoldOutShow（显示）
{
如果（显示！=null）
{
show.IsSoldOut=！show.IsSoldOut；
等待DataService.Shows.UpdateItemAsync（show）；
var message=show.IsSoldOut？“售罄”：“未售罄”；
wait App.Current.MainPage.DisplayAlert（$“Show Updated！”，$“Show:{Show.ShowTitle}已标记为{message}”，“Ok”）；
}
}
}
public partial class ShowsPage : ContentPage
    {
        private ShowsViewModel _viewModel;

        public ShowsPage()
        {
            InitializeComponent();
            BindingContext = _viewModel = new ShowsViewModel();
        }

        protected override void OnAppearing()
        {
            base.OnAppearing();
            _viewModel.OnAppearing();
        }
    }

public class ShowsViewModel : BaseViewModel
    {
        public ObservableCollection<Show> Shows { get; }
        public ObservableCollection<object> SelectedShows { get; }

        public Command SelectionChangedCommand { get; }
        public Command ShowSelectedCommand { get; }
        public Command DeleteMultipleShowsCommand { get; }
        public Command AddShowCommand { get; }
        public Command LoadShowsCommand { get; }
        public Command SwipeIsPublishCommand { get; }
        public Command SwipeIsActiveCommand { get; }
        public Command SwipeIsSoldOutCommand { get; }

        public ShowsViewModel()
        {
            Title = "Shows";
            Shows = new ObservableCollection<Show>();
            SelectedShows = new ObservableCollection<object>();

            LoadShowsCommand = new Command(async () => await LoadItems());
            AddShowCommand = new Command(OnAddItem);
            ShowSelectedCommand = new Command<Show>(OnItemSelected);
            DeleteMultipleShowsCommand = new Command(async () => await DeleteShows(), () => CanDeleteShows());
            SelectionChangedCommand = new Command(DeleteMultipleShowsCommand.ChangeCanExecute);

            SwipeIsPublishCommand = new Command<Show>(async (show) => await PublishShow(show));
            SwipeIsActiveCommand = new Command<Show>(async (show) => await ActivateShow(show));
            SwipeIsSoldOutCommand = new Command<Show>(async (show) => await SoldOutShow(show));
        }

        private async Task LoadItems()
        {
            IsBusy = true;

            try
            {
                Shows.Clear();
                var shows = await DataService.Shows.GetItemsAsync();
                foreach (var show in shows)
                {
                    this.Shows.Add(show);
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex);
            }
            finally
            {
                IsBusy = false;
            }
        }

        public void OnAppearing()
        {
            IsBusy = true;
        }

        private async void OnAddItem(object obj)
        {
            await Shell.Current.GoToAsync(nameof(CreateShowPage));
        }

        private async void OnItemSelected(Show show)
        {
            if (show == null)
                return;

            // This will push the ItemDetailPage onto the navigation stack
            await Shell.Current.GoToAsync($"{nameof(ShowDetailPage)}?{nameof(ShowDetailViewModel.ShowId)}={show.ShowId}");
        }

        private bool CanDeleteShows()
        {
            return SelectedShows.Count() > 0;
        }

        private async Task DeleteShows()
        {
            if (SelectedShows != null && SelectedShows.Count() > 0)
            {
                bool confirm = await App.Current.MainPage.DisplayAlert("Delete?", $"Are you sure you want to delete the selected show(s)?", "Yes", "No");
                if (confirm)
                {
                    IsBusy = true;

                    var totalDeleted = 0;
                    foreach (var showobj in SelectedShows)
                    {
                        var show = (Show)showobj;
                        var response = await DataService.Shows.DeleteItemAsync(show.ShowId.ToString());
                        if (response)
                        {
                            totalDeleted++;
                        }
                    }

                    await App.Current.MainPage.DisplayAlert("Delete Results", $"Deleted {totalDeleted} show(s).", "Ok");

                    // This will reload the page
                    IsBusy = true;
                }
            }
        }

        private async Task PublishShow(Show show)
        {
            if (show != null)
            {
                show.IsPublished = !show.IsPublished;
                await DataService.Shows.UpdateItemAsync(show);

                var message = show.IsPublished ? "published" : "unpublished";
                await App.Current.MainPage.DisplayAlert($"Show Updated!", $"Show: {show.ShowTitle} has been {message}", "Ok");
            }
        }

        private async Task ActivateShow(Show show)
        {
            if (show != null)
            {
                show.IsActive = !show.IsActive;
                await DataService.Shows.UpdateItemAsync(show);

                var message = show.IsActive ? "activated" : "archived";
                await App.Current.MainPage.DisplayAlert($"Show Updated!", $"Show: {show.ShowTitle} has been {message}", "Ok");
            }
        }

        private async Task SoldOutShow(Show show)
        {
            if (show != null)
            {
                show.IsSoldOut = !show.IsSoldOut;
                await DataService.Shows.UpdateItemAsync(show);

                var message = show.IsSoldOut ? "sold out" : "not sold out";
                await App.Current.MainPage.DisplayAlert($"Show Updated!", $"Show: {show.ShowTitle} has been marked as {message}", "Ok");
            }
        }
    }

CommandParameter="{Binding Source={RelativeSource Self}, Path=BindingContext}"

private async void PublishedSwipeItem_Invoked(object sender, System.EventArgs e)
{
  var show = (sender as SwipeItem)?.BindingContext as Show;

  if (show!= null)
    await viewModel.PublishShow(show);
}