COMBOBOX filtering in WPF with MVVM - wpf

Question

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 ?

Answer 1

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>

Answer 2

Is there any easy way to apply filters on the existing list based on
some flag ?
Although your question is not clear, but I think you don't need to maintain two list just to get the filter data. You can use simple LINQ to do the filtering. Suppose if you have a ViewModel Property like
public IEnumerable<ComboBoxItem> Data
{
get ;
set ;
}
And you want to filter that based on some bool values then you can write something like
ViewModel.Data.ToList().Where(item => item.Status).ToList()
Status can be the bool based on that you want to filter your data and you can add this bool inside your ComboBoxItem class.