Bind a RadComboBox to Enum Values
The purpose of this topic is to show you how to build a RadComboBox containing all values of a specific Enum. This is a fairly easy task and can be done in only few steps.
- The best solution here is to create a view model for the Enum:
public class EnumViewModel
{
private Type enumType;
public IEnumerable Values
{
get;
private set;
}
[TypeConverter( typeof( TypeTypeConverter ) )]
public Type EnumType
{
get
{
return this.enumType;
}
set
{
this.enumType = value;
this.InitValues();
}
}
private void InitValues()
{
this.Values = this.EnumType.GetFields( System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Static )
.Select<FieldInfo, object>( ( FieldInfo x ) => x.GetValue( this.EnumType ) );
}
}
Public Class EnumViewModel
Private m_enumType As Type
Private _Values As IEnumerable
Public Property Values() As IEnumerable
Get
Return _Values
End Get
Private Set(ByVal value As IEnumerable)
_Values = value
End Set
End Property
<TypeConverter(GetType(TypeTypeConverter))> _
Public Property EnumType() As Type
Get
Return Me.m_enumType
End Get
Set(ByVal value As Type)
Me.m_enumType = value
Me.InitValues()
End Set
End Property
Private Sub InitValues()
Me.Values = Me.EnumType.GetFields(System.Reflection.BindingFlags.[Public] Or System.Reflection.BindingFlags.[Static]).Select(Function(ByVal x As FieldInfo) x.GetValue(Me.EnumType))
End Sub
End Class
The trick here is the TypeConverter attribute on the EnumType property, that allows you to declare the EnumModel in XAML:
<UserControl.Resources>
<example:EnumViewModel x:Name="DataSource" EnumType="System.Windows.Controls.ClickMode"/>
</UserControl.Resources>
Here is the structure of the TypeTypeConverter class which derives from TypeConverter.
public class TypeTypeConverter : TypeConverter
{
public override bool CanConvertFrom( ITypeDescriptorContext context, Type sourceType )
{
return sourceType.IsAssignableFrom( typeof( string ) );
}
public override object ConvertFrom( ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value )
{
// Try to load the type from the current assembly (EnumValuesInCombo.dll)
Type t = Type.GetType( ( string )value, false );
// If the type is from a different known assembly, try to load it from there
if ( t == null )
{
// Try to load the type from Telerik.Windows.Controls.dll
t = this.GetTypeFromAssembly( value.ToString(), typeof( Telerik.Windows.Controls.ItemsControl ) );
}
if ( t == null )
{
// Try to load the type from System.Windows.dll
t = this.GetTypeFromAssembly( value.ToString(), typeof( System.Windows.Controls.ItemsControl ) );
}
// You can also try with other known assemblies.
//if (t == null)
//{
// t = GetTypeFromAssembly(value.ToString(), typeof(a type that is in the assembly, containing the enum));
//}
return t;
}
private Type GetTypeFromAssembly( string typeName, Type knownType )
{
string assemblyName = knownType.AssemblyQualifiedName;
return Type.GetType( assemblyName.Replace( knownType.FullName, typeName ), false );
}
}
Public Class TypeTypeConverter
Inherits TypeConverter
Public Overloads Overrides Function CanConvertFrom(ByVal context As ITypeDescriptorContext, ByVal sourceType As Type) As Boolean
Return sourceType.IsAssignableFrom(GetType(String))
End Function
Public Overloads Overrides Function ConvertFrom(ByVal context As ITypeDescriptorContext, ByVal culture As System.Globalization.CultureInfo, ByVal value As Object) As Object
' Try to load the type from the current assembly (EnumValuesInCombo.dll)
Dim t As Type = Type.GetType
' If the type is from a different known assembly, try to load it from there
If t Is Nothing Then
' Try to load the type from Telerik.Windows.Controls.dll
t = Me.GetTypeFromAssembly(value.ToString(), GetType(Telerik.Windows.Controls.ItemsControl))
End If
If t Is Nothing Then
' Try to load the type from System.Windows.dll
t = Me.GetTypeFromAssembly(value.ToString(), GetType(System.Windows.Controls.ItemsControl))
End If
' You can also try with other known assemblies.
'if (t == null)
'{
' t = GetTypeFromAssembly(value.ToString(), typeof(a type that is in the assembly, containing the enum));
'}
Return t
End Function
Private Function GetTypeFromAssembly(ByVal typeName As String, ByVal knownType As Type) As Type
Dim assemblyName As String = knownType.AssemblyQualifiedName
Return Type.GetType
End Function
End Class
Take a closer look at the tricky ConvertFrom() method. It does several things:
It tries to load the type from the current assembly.
If the type is from a different known assembly, try to load it from there. For example, the method will try to load the enumeration either from Telerik.Windows.Controls.dll or from System.Windows.dll.
You can also add code, which tries to load the type from other known assemblies.
There are some limitations in this approach, though – you should modify the TypeTypeConverter class so that it can "recognize" the assemblies that might contain the enumerations, defined in XAML. Of course, if you create the EnumModel in the code-behind you will be able to provide any Enum Type you want – in this case the modifications in the TypeTypeConverter class won't be necessary.
- The second step is to find your RadComboBox declaration and to set the EnumModel to the ItemsSource property.
<UserControl.Resources>
<example:EnumViewModel x:Name="DataSource" EnumType="System.Windows.Controls.ClickMode"/>
</UserControl.Resources>
....
<telerik:RadComboBox x:Name="radComboBox"
ItemsSource="{Binding Source={StaticResource DataSource}, Path=Values}">
</telerik:RadComboBox>
- The final step is to set the DisplayMemberPath attribute with empty string value. It has to be present, in order for the RadComboBox to be able to properly display its selected item. If you remove it, the control will display the Enum’s integer value in its selection box, instead of its text representation.
<UserControl.Resources>
<example:EnumViewModel x:Name="DataSource" EnumType="System.Windows.Controls.ClickMode"/>
</UserControl.Resources>
....
<telerik:RadComboBox x:Name="radComboBox"
ItemsSource="{Binding Source={StaticResource DataSource}, Path=Values}" DisplayMemberPath="">
</telerik:RadComboBox>
The result can be seen on the image below. All members of the System.Windows.Controls.ClickMode enumeration are loaded in the RadComboBox.
