I am developing an application using WPF mvvm approach. I have a requirement where I have to show a list of items in a combo box for selection. Based on some flag I need to filter out few items from the combo box for selection.
I tried to use two different items sources one with full list and another with filtered list and based on the flag I wanted to change the items source. This does not seem to be working well. Is there any easy way to apply filters on the existing list based on some flag ?
There are lots of different ways to do this but my personal preference is to use a ListCollectionView
as the ItemsSource of the control displaying the filtered list, to set a filter predicate on ListCollectionView.Filter
and to call ListCollectionView.Refresh
when the filter parameters change.
The example below will filter a list of countries based on their continent.
Code
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows.Data;
public class FilteringViewModel : INotifyPropertyChanged
{
private ObservableCollection<Country> _countries;
private ContinentViewModel _selectedContinent;
public ListCollectionView CountryView { get; set; }
public event PropertyChangedEventHandler PropertyChanged;
public ObservableCollection<ContinentViewModel> Continents { get; set; }
public FilteringViewModel()
{
_countries =
new ObservableCollection<Country>(
new[]
{
new Country() { Continent = Continent.Africa, DisplayName = "Zimbabwe" },
new Country() { Continent = Continent.Africa, DisplayName = "Egypt" },
new Country() { Continent = Continent.Europe, DisplayName = "United Kingdom" }
});
CountryView = new ListCollectionView(_countries);
CountryView.Filter = o => _selectedContinent == null || ((Country)o).Continent == _selectedContinent.Model;
Continents = new ObservableCollection<ContinentViewModel>(Enum.GetValues(typeof(Continent)).Cast<Continent>().Select(c => new ContinentViewModel { Model = c}));
}
public ContinentViewModel SelectedContinent
{
get
{
return _selectedContinent;
}
set
{
_selectedContinent = value;
OnContinentChanged();
this.OnPropertyChanged("SelectedContinent");
}
}
private void OnContinentChanged()
{
CountryView.Refresh();
}
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = this.PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
public class Country
{
public string DisplayName { get; set; }
public Continent Continent { get; set; }
}
public enum Continent
{
[Description("Africa")]
Africa,
Asia,
Europe,
America
}
public class ContinentViewModel
{
public Continent Model { get; set; }
public string DisplayName
{
get
{
return Enum.GetName(typeof(Continent), Model);
}
}
}
XAML
<StackPanel Orientation="Vertical">
<ComboBox ItemsSource="{Binding Continents}" SelectedItem="{Binding SelectedContinent}" DisplayMemberPath="DisplayName" />
<ListBox ItemsSource="{Binding CountryView}" DisplayMemberPath="DisplayName" />
</StackPanel>