wpf组合框-更改绑定后的性能

我有两个组合框。两者的项都是枚举值。根据组合Foo中的选择，Bar组合中有不同的项目（绑定更改）。第一次comboBar总是很快弹出-无论组合Foo以前是否弹出过。但在comboFoo中的每次选择更改后（在comboBar至少弹出一次后）组合栏弹出非常缓慢。我不知道该怎么修。

枚举

public enum Foo
{
    Foo1, Foo2, Foo3
}
public enum Bar
{
    Bar1, Bar2, Bar3, Bar4, Bar5, Bar6, Bar7, Bar8, Bar9, Bar10, 
    Bar11, Bar12, Bar13, Bar14, Bar15, Bar16, Bar17, Bar18,
}

标记枚举

public class EnumValuesExtension : MarkupExtension
{
    private readonly Type enumType;
    public EnumValuesExtension(Type enumType)
    {
        if (enumType == null)
            throw new ArgumentNullException("enumType");
        if (!enumType.IsEnum)
            throw new ArgumentException("Argument enumType must derive from type Enum.");
        this.enumType = enumType;
    }
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return Enum.GetValues(enumType);
    }
}

转换器（用法见下面的方法）

public class EnumToFilteredListConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (!(value is Type))
            return null;
        var enumType = (Type)value;
        if (!enumType.IsSubclassOf(typeof(Enum)))
            return null;
        Array allValues = Enum.GetValues(enumType);
        IEnumerable enumList;
        var filterList = (parameter == null) ? Enum.GetValues(enumType).Cast<Enum>() : (parameter as Array).Cast<Enum>();
        try
        {
            enumList = from Enum enumValue in allValues
                       where filterList.Contains(enumValue)
                       select enumValue;
        }
        catch (ArgumentNullException)
        {
            enumList = allValues;
        }
        catch (ArgumentException)
        {
            enumList = allValues;
        }
        return enumList;
    }
    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

SelectionChanged方法（代码隐藏）

    private void cboFoo_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (comboBar == null)
            return;
        if (comboFoo.SelectedItem == null)
            return;
        var binding = new Binding
                          {
                              Source = typeof(Bar),
                              Converter = new EnumToFilteredListConverter()
                          };
        switch ((Foo)comboFoo.SelectedItem)
        {
            case Foo.Foo1: // Show only Bar1-Bar3
                binding.ConverterParameter = new Enum[] { Bar.Bar1, Bar.Bar2, Bar.Bar3 };
                break;
            case Foo.Foo2: // Show only Bar3-Bar5
                binding.ConverterParameter = new Enum[] { Bar.Bar3, Bar.Bar4, Bar.Bar5 };
                break;
            default: // Show all of Bar
                binding.ConverterParameter = null;
                break;
        }
        comboBar.SetBinding(ItemsControl.ItemsSourceProperty, binding);
    }

XAML

<StackPanel>            
    <ComboBox Name="comboFoo" ItemsSource="{Binding Source={markup:EnumValues {x:Type types:Foo}}}" SelectionChanged="cboFoo_SelectionChanged" />
    <ComboBox Name="comboBar" ItemsSource="{Binding Source={markup:EnumValues {x:Type types:Bar}}}" />
    <!--<ListBox Name="comboBar" ItemsSource="{Binding Source={markup:EnumValues {x:Type types:Bar}}}" />-->
</StackPanel>

如果我使用列表框而不是comboBar，我没有任何性能问题，所以我认为问题不属于转换器。。。

PS:VS2010、.NET4.0、调试构建以及发布构建测试