CollectionViewSource with custom sort

Question

I'm new to WPF and I'm having difficulty trying to sort a CollectionViewSource with a custom sort. Here's the situation:

I have a SearchView that is called with a parameter which becomes it's datacontext like so:

mainView.SetGlobalOverlay(New SearchView With {.DataContext = interventionViewModel})

In the SearchView.xaml, I then bind the CollectionViewSource to the collection :

<CollectionViewSource x:Key="UnitsCollection"
                          Filter="UnitsCollection_Filter"
                          Source="{Binding Path=Units}" />

Now, I already have an IComparer interface implemented in another shared class. This comparer is used on a ListCollectionView somewhere else in the sourcecode and works fine. Now, how can I re-use this comparer on a CollectionViewSource?

Answer 1

In order to use the custom sorter for the CollectionViewSource, you have to wait until the ItemsControl (e.g. a list box) is loaded; then you can get the ListCollectionView using the View property of the CollectionViewSource.

As illustration, here is a small example that displays a list of integers in two different ways: the upper list box applies a custom sort order, whereas the lower list box is unsorted:

MainWindow.xaml:

<Window x:Class="WpfApplication27.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:clr="clr-namespace:System;assembly=mscorlib"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="300">
    <Window.Resources>
        <CollectionViewSource x:Key="MyCollectionViewSource1" Source="{Binding RawData}" />
        <CollectionViewSource x:Key="MyCollectionViewSource2" Source="{Binding RawData}" />
    </Window.Resources>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <ListBox Grid.Row="0" Margin="5" Background="LightSkyBlue"
                 ItemsSource="{Binding Source={StaticResource MyCollectionViewSource1}}"/>
        <ListBox Grid.Row="1" Margin="5" Background="LightYellow"
                 ItemsSource="{Binding Source={StaticResource MyCollectionViewSource2}}"/>
    </Grid>
</Window>

MainWindow.xaml.cs:

using System.Collections;
using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Data;

namespace WpfApplication27
{
    public partial class MainWindow : Window
    {
        public ObservableCollection<int> RawData { get; private set; }

        public MainWindow()
        {
            RawData = new ObservableCollection<int> { 10, 222, 1, 333, 2, 777, 6 };

            InitializeComponent();

            DataContext = this;            

            this.Loaded += MainWindow_Loaded;
        }

        void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            CollectionViewSource source = (CollectionViewSource)(this.Resources["MyCollectionViewSource1"]);
            ListCollectionView view = (ListCollectionView)source.View;
            view.CustomSort = new CustomSorter();
        }
    }

    // Sort by number of digits (descending), then by value (ascending)
    public class CustomSorter : IComparer
    {
        public int Compare(object x, object y)
        {
            int digitsX = x.ToString().Length;
            int digitsY = y.ToString().Length;
            if (digitsX < digitsY)
            {
                return 1;
            }
            else if (digitsX > digitsY)
            {
                return -1;
            }
            return (int) x - (int) y;
        }
    }
}