使用LinQ过滤ObservableCollection

Question

I have a MVVM application and I am trying to make filtering through LinQ work on my ObservableCollection that is gotten from database based on Entity Framework.

In View Model I have this:

public class MenuListViewModel : BaseViewModelCollection<Menu>

{
    private string filterString;

    public string FilterString
    {
        get { return filterString; }
        set
        {
            if (Equals(value, filterString)) return;
            filterString = value;
            RaisePropertyChanged();
        }
    }

    //TODO problems with notification, filter doesn't work
    public ObservableCollection<Menu> FilteredItems
    {
        get
        {
            if (filterString == null) return Items; //Items is Observable Collection that contains every Item
            var query = Items.Where(x => x.Time.ToString().StartsWith(filterString));
            return new ObservableCollection<Menu>(query);
        }
    }

    public MenuListViewModel(MenuService menuService)
    {
        base.Service = menuService; //Using IoC to get service
    }
}

In Xaml I have the following Binding:

 <TextBox x:Name="RecipeFilterBox" Margin="5,5,0,0" TextWrapping="Wrap" Text="{Binding FilterString, NotifyOnTargetUpdated=True}" Grid.Column="1" Height="47.07" VerticalAlignment="Top"/>

The thing is that when I write anything in the TextBox, nothing changes. I know that there is something wrong with the propertyChanged event, but I really can't figure out how to fix this. If you need any more information about this app, just ask me.

EDIT: The xaml for FilteredItems looks like this:

    <ListBox x:Name="MenuItemsListView" ItemsSource="{Binding FilteredItems}" SelectedItem="{Binding DeletedItem, Mode=OneWayToSource}" Foreground="#FFFFEDD3" FontFamily="Segoe Print" FontWeight="Bold" FontSize="18.667" Grid.ColumnSpan="3" Grid.Row="1" ItemContainerStyle="{DynamicResource ListBoxItemStyle1}" Style="{DynamicResource ListBoxStyle1}">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <StackPanel Orientation="Horizontal">
                    <TextBlock Text="{Binding Recipe.Name}" Width="255"/>
                    <TextBlock Width="175" Text="{Binding Time, Converter={StaticResource EnumTimeToItsDescriptionValueConverter}, Mode=OneWay}" />
                    <TextBlock Text="{Binding Date, StringFormat=dd.MM.yyyy}"/>
                </StackPanel>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>

Answer 1

you can achieve this using ICollectionView .

use FilteredItems as the underlying source of the ICollectionView and expose ICollectionView to your view instead of ObservableCollection<Menu>

Use the filter delegate to provide the filter logic

FilteredItems.Filter = item =>
{
    Menu m = item as Menu;
    return m.Time.ToString().StartsWith(FilterString);
}

and when FilterString changes invoke FilterItems.Refresh();

Here is an example:

public class MenuListViewModel : BaseViewModelCollection<Menu>
{
   public MenuListViewModel()
   {
      var data = new List<Menu> { some data ... }; // your real list of menus
      // initialize the collection view
      FilteredItems = CollectionViewSource.GetDefaultView(data);
      // apply filtering delegate
      FilteredItems.Filter = i =>
      {
         // This will be invoked for every item in the underlying collection 
         // every time Refresh is invoked
         if (string.IsNullOrEmpty(FilterString)) return true;
         Menu m = i as Menu;
         return m.Time.ToString().StartsWith(FilterString);
      };
   }

   private string filterString;
   public string FilterString
   {
       get { return filterString; }
       set
       {
           if (Equals(value, filterString)) return;
           filterString = value;
           FilteredItems.Refresh(); // tirggers filtering logic
           RaisePropertyChanged("FilterString"); 
       }
   }

    public ICollectionView FilteredItems { get; set; }
}

You would also have to change the UpdateSourceTrigger on your filter TextBox to make it update the FilterString every time the user changes the text.

Text="{Binding FilterString, UpdateSourceTrigger=PropertyChanged, ...}

Answer 2

Add RaisePropertyChanged("FilteredItems") inside FilterString setter. FilteredItems property changed is never raised so bindings doesn't work the way you expect.