I have two comboboxes. The items of both are enum values. Depending on selection in comboFoo there are different items available in comboBar (binding change). The first time comboBar always pops up quickly - no matter wether comboFoo has popped up before or not. But after every selection change in comboFoo (after comboBar has popped up at least one time) comboBar pops up very slowly. I have not any idea how to fix it.
Enums
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,
}
Mark up for enums
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);
}
}
Converter (usage see method below)
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 method (code behind)
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>
If I use a listbox instead of comboBar I have not any performance problem, so I think the problem does not belong to the converter...
PS: VS2010, .NET4.0, Debug-Build and also Release-Build tested