如何使用DataTemplate实现对WPF ListBox的搜索？

Question

I'd like to implement search for a WPF prototype I'm building in which I'm using a ListBox with a DataTemplate. I'm trying to devise a way to search the text value of a few TextBlock controls on each item and then set the Visibility to Collapsed on any items that don't contain the search text.

I figure that one way I could do this would be to include a property on the Model to which the ListBox Items are bound, bind the Item's Visibility property to that Model property via a ValueConverter, and set that property during search, but seems kind of kludgy to me. Any and all thoughts are appreciated! Thank you!

Answer 1

The simplest answer would be to use a CollectionViewSource(CVS) to contain your collection, and have the listbox bound to the CVS. CVS can perform filters, sorts, and groups without affecting the collection.

CODEBEHIND Method

Essentially you will have an event handler which tells the CVS to perform a new filter as delegate. Mine generally look something like this:

Private Sub MyEventHandler()
    _ShipmentCollectionView.Filter = New Predicate(Of Object)(AddressOf FilterOut)
End Sub

Private Function FilterOut(ByVal item As Object) As Boolean
        Dim MyShipment As Shipment = CType(item, Shipment)
        If _FilterDelivered And MyShipment.TransitStatus = eTransitStatus.Delivered Then
            Return False
        End If
        If _FilterOverdue And MyShipment.TransitStatus = eTransitStatus.InTransit AndAlso MyShipment.ExpectedDate < Today Then
            Return False
        End If
        If _FilterUnshipped And MyShipment.TransitStatus = eTransitStatus.Unshipped Then
            Return False
        End If
        If SearchString Is Nothing Or SearchString = "" Then
            Return True
        Else

            Return MyShipment.Contains(SearchString)
        End If
    End Function

What this does is pass the items through that FilterOut method, and return whether or not they fit the filter. If they do, the CollectionView (or which the CVS is a part) tells the UI which items to display.

The MVVM Method

(My Favorite)

This method differs in that all filter option controls are bound to properties in the ViewModel. My favorite thing to do with this is to put the _ShipmentCollectionView.Filter = New Predicate(Of Object)(AddressOf FilterOut) line in the SearchText property setter. This way, the filter operation is run every time a user types a letter (Continuous Filtering), that is presuming they have the binding made correctly (ie Text="{Binding SearchString, UpdateSourceTrigger=PropertyChanged}")

Personally I recommend MVVM pattern for all but the simplest projects. It allows for a lot more neat stuff to be done with a lot less hassle.

Hope that helps.

Links!

• MSDN CollectionViewSource Article
• MSDN CollectionViewSource Filter Article

Answer 2

I've found the easiest way is to apply Filter to the CollectionViewSource , rather than updating each item individually.

public ObservableCollection<MyObject> Entries { get; set; }
public CollectionViewSource View { get; set; }

private string _searchText;
public string SearchText
{
    get { return _searchText; }
    set
    {
        if (_searchText == value)
            return;
        _searchText = value;
        View.Filter -= ApplySearch;
        if (!string.IsNullOrWhiteSpace(_searchText))
            View.Filter += ApplySearch;
    }
}

public MyClass()
{
    Entries = new ObservableCollection<MyObject>();
    View = new CollectionViewSource { Source = Entries };
}

private void ApplySearch(object sender, FilterEventArgs e)
{
        var item = e.Item as MyObject;
        if (item == null)
            return;
        if (item.FirstProperty.IndexOf(SearchText) < 0 && item.SecondProperty.IndexOf(SearchText) < 0)
            e.Accepted = false;
}

Note: In this case there's no need for a search button, but it may be a good idea to use a DispatcherTimer to set a delay before setting the filters.

Answer 3

Use CollectionView:

ICollectionView collectionView = CollectionViewSource.GetDefaultView(_source);
collectionView.Filter = new Predicate<object>(YourFilterFunction);