exposed filter - Page 34

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Filtering in a HierarchicalDataTemplate via MarkupExtension?

I'm trying to create a MarkupExtension to allow filtering of items in an ItemsSource of a HierarchicalDataTemplate. In particular, I'd like to be able to supply a method name that will be executed on the DataContext in order to perform the filtering. The usage syntax I'm after looks like this: <HierarchicalDataTemplate DataType="{x:Type src:DeviceBindingViewModel}" ItemsSource="{Utilities:FilterCollection {Binding Definition.Entries}, MethodName=FilterEntries}"> <StackPanel Orientation="Horizontal"> <Image Source="{StaticResource BindingImage}" Width="24" Height="24" Margin="3"/> <TextBlock Text="{Binding DisplayName}" FontSize="12" VerticalAlignment="Center"/> </StackPanel> </HierarchicalDataTemplate> My code for the custom MarkupExtension looks like this: public sealed class FilterCollectionExtension : MarkupExtension { private readonly MultiBinding _binding; private Predicate<Object> _filterMethod; public string MethodName { get; set; } public FilterCollectionExtension(Binding binding) { _binding = new MultiBinding(); _binding.Bindings.Add(binding); //We package a reference to the DataContext with the binding so that the Converter has access to it var selfBinding = new Binding {RelativeSource = RelativeSource.Self}; _binding.Bindings.Add(selfBinding); _binding.Converter = new InternalConverter(this); } public FilterCollectionExtension(Binding binding, string methodName) : this(binding) { MethodName = methodName; } public override object ProvideValue(IServiceProvider serviceProvider) { return _binding; } private bool FilterInternal(Object dataContext, Object value) { //Filtering is only applicable if a DataContext is defined if (dataContext != null) { if (_filterMethod == null) { var type = dataContext.GetType(); var method = type.GetMethod(MethodName, new[] { typeof(Object) }); if (method == null || method.ReturnType != typeof(bool)) throw new InvalidOperationException("Could not locate a filter predicate named " + MethodName + " on the DataContext"); _filterMethod = (Predicate<Object>)Delegate.CreateDelegate(typeof(Predicate<Object>), dataContext, method); } else { if (_filterMethod.Target != dataContext) { _filterMethod = (Predicate<Object>) Delegate.CreateDelegate(typeof (Predicate<Object>), dataContext, _filterMethod.Method); } } if (_filterMethod != null) return _filterMethod(value); } //If no filtering resolved, just allow all elements return true; } private class InternalConverter : IMultiValueConverter { private readonly FilterCollectionExtension _owner; public InternalConverter(FilterCollectionExtension owner) { _owner = owner; } public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture) { var enumerable = values[0]; var targetElement = (FrameworkElement)values[1]; var view = CollectionViewSource.GetDefaultView(enumerable); view.Filter = item => _owner.FilterInternal(targetElement.DataContext, item); return view; } public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture) { throw new NotSupportedException("Cannot convert back"); } } } I can see that the extension is instantiated and I can see it return the MultiBinding that is used by the Template. I also see the call to the InternalConverter.Convert method, which sees the expected parameters (I see the collection provided by the nested {Binding}) and is successfully able to retrieve the ICollectionView for the incoming collection. The only problem is that FilterInternal never gets called. The template is ultimately being used by a TreeView, if that's relevant. I haven't been able to figure out why the FilterInternal method is not being called and I was hoping somebody might be able to offer some insight.

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