未显示分组集合视图列表，可能存在绑定错误

Question

我刚开始使用 MVVM 布局，我的collectionView 列表中似乎无法显示任何内容。我相信这是我的绑定，不幸的是我真的不明白我应该如何绑定分组列表+ ViewModel。我读到绑定到没有源的路径，但我很确定我做错了。我已经检查过是否我什至可以加载共享，而我是，它们只是没有显示。

模型 -- 分享

 [JsonProperty("iSpottedID")]
 public int ID { get; set; }

 [JsonProperty("sShoppingList")]
 [MaxLength(255)]
 public string ShoppingName { get; set; }

 [JsonProperty("dtInfoUpdate")]
 [MaxLength(20)]
 public string CreateDate { get; set; }

 [JsonProperty("iProductID")]
 public int ProductID { get; set; }

 [Indexed]
 [JsonProperty("sLocation")]
 [MaxLength(255)]
public string LocationName { get; set; }

 [JsonProperty("tvCardJson")]
 public string JsonString { get; set; }

ViewModel -- SharesViewModel 公共类 SharesViewModel : BaseViewModel { #region 属性

    private int _id;
    public int ID
    {
        get { return _id;  }
        set
        {
            SetValue(ref _id, value);
            OnPropertyChanged(nameof(ID));
        }
    }

    private string _longName;
    public string LongName
    {
        get { return _longName; }
        set
        {
            SetValue(ref _longName, value);
            OnPropertyChanged(nameof(LongName));
        }
    }

    private string _date;
    public string CreateDate
    {
        get{ return _date;}
        set
        {

            SetValue(ref _date, value);
            OnPropertyChanged(nameof(CreateDate));
        }
    }

    private int _prodID;
    public int ProductID
    {
        get { return _id; }
        set
        {
            SetValue(ref _prodID, value);
            OnPropertyChanged(nameof(ProductID));
        }
    }

    private string _json;
    public string JsonString
    {
        get { return _json; }
        set
        {
            SetValue(ref _json, value);
            OnPropertyChanged(nameof(JsonString));
        }
    }

   
    private string _location;
    public string LocationName
    {
        get { return _location; }
        set
        {
            SetValue(ref _location, value);
            OnPropertyChanged(nameof(LocationName));
        }
    }

    //ADD-ONS
    public string Address
    {
        get
        {
            if (!string.IsNullOrEmpty(JsonString))
            {
                var jsonDict = JsonConvert.DeserializeObject<Dictionary<string, string>>(JsonString);
                if (jsonDict.ContainsKey("address"))
                    if (jsonDict["address"] != "")
                        return jsonDict["address"];
            }
            return null;
        }
    }

    private ImageSource _imageLink;
    public ImageSource ImageLink
    {
        get
        {
            if(ProductID != 0)
            {
               ...
                 return ImageSource.FromUri(link);
            }
            return null; 
        }
    }

    #endregion

    public SharesViewModel(){}
    public SharesViewModel(Share share)
    {
        ID = share.ID;
        ProductID = share.ProductID;
        JsonString = share.JsonString;
        CreateDate = share.CreateDate;
        LocationName = share.LocationName;
    }

列表视图模型 -- SharesListViewlModel

  public class SharesListViewModel : BaseViewModel
    {
        
private SharesViewModel _selectedShare;
private bool _isDataLoaded;
//grouped list
public ObservableCollection<LocationSpotGroups<string, SharesViewModel>> Shares { get;  set; }
...
public ICommand OpenMoreSharesCommand { get; private set; }
public ICommand LoadDataCommand { get; private set; }
public SharesListViewModel(Position NW , Position SE)
   {
     _nw = NW;
     _se = SE;

     LoadDataCommand = new Command(async () => await LoadData());
     OpenMoreSharesCommand = new Command<SharesViewModel>(async (share) => await OpenMoreShares(share));
      public ObservableCollection<SharesViewModel> sList { get;  set; }
      = new ObservableCollection<SharesViewModel>();
   }

  private async Task LoadData()
        {
            if (_isDataLoaded)
                return;

          
            var list = await _connection.GetAllRegionShares(_nw, _se);
            foreach (var spot in list)
            {
               sList.Add(new SharesViewModel(spot));
            }

            var sorted = from item in sList
                         orderby item.LocationName
                         group item by item.LocationName into itemGroup
                         select new LocationSpotGroups<string, SharesViewModel>(itemGroup.Key, itemGroup);

            Shares = new ObservableCollection<LocationSpotGroups<string, SharesViewModel>>(sorted);
        }

LocationSpotGroups

 public class LocationSpotGroups<K, T> : ObservableCollection<T>
    {
        
        public K GroupKey { get; set; }
        public IEnumerable<T> GroupedItem { get; set; }
      

        public LocationSpotGroups(K key, IEnumerable<T> shares) 
        {
            GroupKey = key;
            GroupedItem = shares;

            foreach (var item in shares)
            {
                this.Items.Add(item);
            }
        }
    }

SharesPage XAML

  <CollectionView x:Name="CollectionList"
                           VerticalOptions="FillAndExpand"
                           ItemsSource="{Binding Shares}"
                           IsGrouped="True">
               <!--HEADER-->
               <CollectionView.GroupHeaderTemplate>
                   <DataTemplate>
                       <StackLayout Orientation="Horizontal"
                                    Padding="5"
                                    BackgroundColor="#f7f7fb">

                           <Label x:Name="labelname"
                                  Text="{Binding GroupKey}"
                                  HorizontalOptions="Start"
                                  VerticalOptions="Center"
                                  TextColor="gray" />
                       </StackLayout>
                   </DataTemplate>
               </CollectionView.GroupHeaderTemplate>

  <CollectionView.ItemsLayout>
                <GridItemsLayout Orientation="Vertical" Span="2" />
            </CollectionView.ItemsLayout>

               <!--BODY-->
            <CollectionView.ItemTemplate>
                <DataTemplate>
                    <Grid Padding="5" Margin="8">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="*" />
                            <ColumnDefinition Width="50" />
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto" />
                            <RowDefinition Height="Auto" />
                            <RowDefinition Height="Auto" />
                        </Grid.RowDefinitions>
                        <ImageButton Source="{Binding ImageLink}"
                               WidthRequest="150"
                               HeightRequest="150"
                               Grid.ColumnSpan="2"
                               CornerRadius="15"
                               Aspect="AspectFill"
                               Grid.Row="0"
                               Grid.Column="0"/>
                        
                        <Label Text="{Binding ShoppingName}"
                               Grid.Row="1"
                               Grid.Column="0"/>

                         <Label Text="More"
                                Grid.Row="1"
                                Grid.Column="1"
                                HorizontalTextAlignment="End"/>

                        <Label Text="{Binding CreateDate}"
                               Grid.Row="2"
                               Grid.Column="0"/>
                                         </Grid>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>

SharesPage CS

 public SharesPage( Position NW, Position SE )
        {
            InitializeComponent();
            ViewModel = new SharesListViewModel(NW, SE);
        }


        public SharesListViewModel ViewModel
        {
            get { return BindingContext as SharesListViewModel; }
            set { BindingContext = value; }
        }
        protected override void OnAppearing()
        {
            ViewModel.LoadDataCommand.Execute(null);
            base.OnAppearing();

        }

Answer 1

如果数据不是很多，则在构造函数中加载数据是有效的，这不是我的情况。一切都完美加载。