Filter an observable collection

Question

I have a ListView control that displays items from an observable collection. These items need to be filtered. I am able to do that with a CollectionViewSource, but the filter needs to be updated each time an item changes.

My items looks like this:

enum Status {Done, Failed, Skipped, ...}

class Project {
  public string Name {get;set;}
  public Status Status {get;set;}
  // etc. etc.
}

class ProjectViewModel : INotifyPropertyChanged {
  private Project project;

  public ProjectBuildInfoViewModel(ProjectBuildInfo project)
  {
    this.project = project;
  }

  public string Name
  {
     get { return project.Name; }
     set { project.Name = value; OnPropertyChanged("Name"); }
  }

  // etc. etc.
}

class CollectionViewModel {
  private ObservableCollection<ProjectViewModel> projects = 
             new ObservableCollection<ProjectViewModel>();

  public ObservableCollection<ProjectViewModel> Collection
  {
     get { return projects; }
     private set {projects = value; }
  } 
}

Then I have this ListView whose ItemSource is bound to the collection.

// member of the user control class
private CollectionViewModel collection = new CollectionViewModel();

// in the constructor
listView.ItemSource = collection.Collection.

This doesn't filter anything. So I have these check boxes and they should indicate which items (depending of the state) should be displayed. I have used then a CollectionViewSource:

private void UpdateView()
{
  var source = CollectionViewSource.GetDefaultView(collection.Collection);
  source.Filter = p => Filter((ProjectViewModel)p);
  listStatus.ItemsSource = source;
}

The filter method looks like this:

private bool Filter(ProjectViewModel project)
{
     return (ckFilterDone.IsChecked.HasValue && ckFilterDone.IsChecked.Value && project.Status == Status.Done) ||
            (ckFilterFailed.IsChecked.HasValue && ckFilterFailed.IsChecked.Value && project.Status == Status.Failed) ||
            (ckFilterSkipped.IsChecked.HasValue && ckFilterSkipped.IsChecked.Value && project.Status == Status.Skipped);
}

This has the disadvantage that it captures the values of the checkboxes, so I have to call this method (UpdateView) each time a checkbox is checked. But it works.

However, the item state does change and if "done" is not checked for instance, when an item goes into "done" it should be removed from the view. Obviously that doesn't change unless I again call UpdateView. So I need to call this method each time something changes. That looks ugly and inefficient to me.

So my question is, can this be done in a nicer way?

Answer 1

Bind your ListView directly to the filtered collection instead of the ObservableCollection by creating a property -

public ICollectionView YourFilteredCollection
{
   get
   {      
      var source = CollectionViewSource.GetDefaultView(collection.Collection);
      source.Filter = p => Filter((ProjectViewModel)p);
      return source;
   }
}

So, now simply you need to call Refresh() on your collection on your check boxes state changed event like this -

YourFilteredCollection.Refresh();

To refresh the collection based on any state change in the item class, you can generalize it by hooking the PropertyChanged event of your item class (for this your class need to implement INotifyPropertyChanged) and from there you can call refresh like this -

foreach (YourClass item in collection.Collection)
{
  item.PropertyChanged += new PropertyChangedEventHandler(item_PropertyChanged);
}

void item_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
  YourFilteredCollection.Refresh();
}

So, whenever any property changes in your item class, your collection will be filtered.