ListBox ItemsSource dynamic filter WPF

Question

Hi

I want to make a UI virtualization via the datasource.

The idea is to "Filter" what i send to the UI (a listbox in my case).

I noticed that the ItemsSource (an observable collection) is read once and that changing the Filter does not trigger refreshing...

I don't understand why Thanks Jonathan

Answer 1

What filter are you talking about? If you are a CollectionView and then binding to that then there won't be a changed even for the control to pick up on.

Answer 2

I'll try to be more clear :

I have CollectionViewSource:

<CollectionViewSource x:Key="MyItemView"
                                  Source="{Binding Path=Model.CurrentItem}" />

Then use this datasource in my ListBox:

<ListBox x:Name="myListBox"
                 ItemsSource="{Binding Source={StaticResource MyItemView}}"

I thought to implement a converter that would return a filtered collection (base on the current date):

<ListBox x:Name="myListBox"
                 ItemsSource="{Binding Source={StaticResource MyItemView}, Converter={StaticResource FilterByTime}, ConverterParameter=CurrentDate }"

Which i implemented this way:

public class FilterByTimeConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value != null)
            {
                System.Windows.Data.ListCollectionView list = value as System.Windows.Data.ListCollectionView;

                var model = DI.Resolve<ApplicationModel>();

                list.Filter = delegate(object item) 
                { 
                    bool r= (((MyModel)item).OriginalDate > model.TimeLine.CurrentDate.AddMonths(-1) 
                        && (((MyModel)item).OriginalDate < model.TimeLine.CurrentDate.AddMonths(1)));

                   // Console.WriteLine ("{0}<{1}<{2} : {3}",model.MyListBox.CurrentDate.AddMonths(-1),((MyModel)item).OriginalDate ,model. MyListBox.CurrentDate.AddMonths(1),r.ToString());
                    return r;
                };

                return list;
            }

            return DependencyProperty.UnsetValue;
        }

This works fine...but only when bounf the first time. When the Current Date is changed and that the filter is changed, the list is not updated.

Perhaps i should listen to the CurrentDate PropertyChange, but i'm confused how to do this

Thanks Jonathan

Answer 3

The CollectionViewSource itself supports filtering via its Filter property. Why don't you put your filtering logic in there?

HTH, Kent

Answer 4

You might want to manually refresh:

currentViewSource.View.Refresh()

Answer 5

Well, I had similar issue, but came with the following solution that works for me:

Supposedly, the combobox shows the list of authors and the listbox all books and I want to filter the books by selected author or show all books unfiltered.

The pertinent window XAML fragment:

<ComboBox ItemsSource="{Binding Authors}"  DisplayMemberPath="FullName" SelectedValue="{Binding FilterAuthorBy, Mode=TwoWay}" />
<ListBox Name="bookList" ItemsSource="{Binding Books}"/>

Binding itself is done like this on the window constructor:

DataContext = new BookViewModel(this);

And the view model is defined as such:

public class BookViewModel
{
   private Author _filterAuthorBy;

   public BookViewModel(IBookView view)
   {
      ...
      _books = new CollectionViewSource();
      _books.Source = _bookRepository.FindAll().ToArray();
      _books.Filter += (sender, e) =>
                         {
                             Book book = e.Item as Book;
                             if (_filterAuthorBy == null)
                             {
                                 e.Accepted = true;
                             }
                             else
                             {
                                 e.Accepted = book.Authors.Contains(_filterAuthorBy);
                             }
                         };
   }

   public CollectionView Books
   {
       get
       {               
           return _books.View;
       }
   }

   public ObservableCollection<Author> Authors
   {
      get
      {
         return new ObservableCollection<Author>(_bookRepository.FindAllAuthors());
      }
   }

   public Author FilterAuthorBy
   {
       get
       {
           return _filterAuthorBy;
       }
       set
       {
           _filterAuthorBy = value;
           _books.View.Refresh();
       }
    } 
}

The selected author is passed down to the ViewModel and the listbox is updated by calling collectionViewSource.View.Refresh()