ICollectionView Issue

Question

I have two ICollectionViews bound to two xaml ListBoxes

If I remove the Filter assignment, I get image 1 (to be expected, but leaving them in gives nothing in the ListBox, I would expect the left one to be populated as all data has Selected = false;

Am I missing something?

using System.Collections.Generic;  
using System.ComponentModel;  
using System.Windows.Data;  
using Microsoft.Toolkit.Mvvm.ComponentModel;  
// ReSharper disable MemberCanBePrivate.Global  
  
namespace UserControls.DualListUserControls;  
  
public abstract class AbstractDualListViewModel<T> : ObservableObject where T : IDisplayString  
{  
    protected AbstractDualListViewModel(IEnumerable<T> sourceList)  
    {  
        Source = CollectionViewSource.GetDefaultView(sourceList);  
        Source.Filter += FalseFilter;  
        Source.Refresh();  
        Destination = CollectionViewSource.GetDefaultView(sourceList);  
        Source.Filter += TrueFilter;  
        Destination.Refresh();  
    }  
  
    public ICollectionView Destination { get; set; }  
  
    public ICollectionView Source { get; set; }  
  
    private bool TrueFilter(object obj)  
    {  
        var ids = (T) obj;  
        return ids.Selected;  
    }  
  
    private bool FalseFilter(object obj)  
    {  
        var ids = (T) obj;  
        return !ids.Selected;  
    }  
}  

Answer 1

If you want to filter by Selected, bind the ICollectionView of Selected=false data to the ListBox on the left, and bind the ICollectionView of Selected=true data to the ListBox on the right, you could try to use the following method.
UserControl1.xaml:

<Grid>  
    <Grid.ColumnDefinitions>  
        <ColumnDefinition Width="*" />  
        <ColumnDefinition Width="Auto" />  
        <ColumnDefinition Width="*" />  
    </Grid.ColumnDefinitions>  
    <ScrollViewer Grid.Column="0" VerticalScrollBarVisibility="Auto">  
        <ListBox   ItemsSource="{Binding Source}">  
            <ListBox.ItemTemplate>  
                <DataTemplate>  
                    <CheckBox  IsChecked="{Binding Selected, Mode=TwoWay}"  
                Content="{Binding DisplayString}"/>  
                </DataTemplate>  
            </ListBox.ItemTemplate>  
        </ListBox>  
    </ScrollViewer>  
    <StackPanel Grid.Column="1" VerticalAlignment="Center">  
        <Button Content="&lt;" />  
        <Button Content="&lt;&lt;"  />  
        <Button Content="&gt;" />  
        <Button Content="&gt;&gt;"  />  
    </StackPanel>  
    <ScrollViewer Grid.Column="2" VerticalScrollBarVisibility="Auto">  
        <ListBox    ItemsSource="{Binding Destination}"  >  
            <ListBox.ItemTemplate>  
                <DataTemplate>  
                    <CheckBox  IsChecked="{Binding Selected, Mode=TwoWay}"  
                Content="{Binding DisplayString}"/>  
                </DataTemplate>  
            </ListBox.ItemTemplate>  
        </ListBox>  
    </ScrollViewer>  
  
</Grid>  

UserControl1.xaml.cs:

using System;  
using System.Collections.Generic;  
using System.Collections.ObjectModel;  
using System.ComponentModel;  
using System.Runtime.CompilerServices;  
using System.Windows.Controls;  
using System.Windows.Data;  
  
namespace UserControl1  
{  
  public partial class UserControl1 : UserControl  
  {  
    SampleDualListViewModel vm;  
    public UserControl1()  
    {  
      InitializeComponent();  
      vm=new SampleDualListViewModel();  
      this.DataContext=vm;  
  
    }  
  }  
  public class SampleDualListViewModel  
  {  
    SampleData sampleData;  
    public ICollectionView Destination { get; set; }  
    public ICollectionView Source { get; set; }  
    public CollectionViewSource CvsSelected{ get;set;}  
    public CollectionViewSource CvsNotSelected{ get;set;}  
    private ObservableCollection<SampleData> data;  
    public ObservableCollection<SampleData> Data   
    {  
      get { return data; }  
      set  
      {  
        data = value;  
      }  
    }  
    public IEnumerable<SampleData> Items { get { return data; } }  
    public SampleDualListViewModel()  
    {  
      data = new ObservableCollection<SampleData>();  
      for (int i = 0; i< 20; i++)  
        {  
          sampleData = new SampleData(){ DisplayString= $"Line {i}", Selected= i % 2 == 0 };  
          data.Add(sampleData);  
        }  
      CvsSelected = new CollectionViewSource();  
      CvsSelected.Source=Data;  
      CvsSelected.Filter += (s, e) =>  
      {  
        SampleData sd=e.Item as SampleData;  
        e.Accepted = sd.Selected;  
      };  
      Destination = CvsSelected.View;  
      Destination.Refresh();  
  
      CvsNotSelected = new CollectionViewSource();  
      CvsNotSelected.Source = Data;  
      CvsNotSelected.Filter += (s, e) =>  
      {  
        SampleData sd = e.Item as SampleData;  
        e.Accepted = !sd.Selected;  
      };  
      Source = CvsNotSelected.View;  
      Source.Refresh();  
    }  
  
  }  
     
    public class SampleData : INotifyPropertyChanged  
  {  
    public SampleData() { }  
    public SampleData(string s)  
    {  
      DisplayString = s;  
    }  
    private string displayString;  
    public string DisplayString   
    {  
      get { return displayString; }  
      set  
      {  
        displayString = value;  
        OnPropertyChanged("DisplayString");  
      }  
    }  
    private bool selected;  
    public bool Selected  
    {  
      get { return selected; }  
      set  
      {  
        selected = value;  
        OnPropertyChanged("Selected");  
      }  
    }  
    public event PropertyChangedEventHandler PropertyChanged;  
    protected void OnPropertyChanged([CallerMemberName] string name = null)  
    {  
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));  
    }  
  }  
}  

MainWindow.xaml:(Test)

 <Window x:Class="Test.MainWindow"  
            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
            xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
            xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
            xmlns:local="clr-namespace:Test"  
            xmlns:dualListUserControls="clr-namespace:UserControls.DualListUserControls;assembly=UserControls"  
            xmlns:uc="clr-namespace:UserControl1;assembly=UserControl1"  
            mc:Ignorable="d"  
            Title="MainWindow" Height="407" Width="300">  
      
        <StackPanel >  
            <uc:UserControl1  Height="300" />  
        </StackPanel>  
    </Window>  

The result:

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Answer 2

s!AoEHbi5A2zZel_gSzzIMIXfzLj_C7A

Here is a link to the whole solution, UserControl library and test project: