Mapping Converters

• Nov 29, 2023
• 2 minutes to read

Mapping converters allow you to apply custom logic to mapping.

Overview

Converters can change data from one type to another, translate data based on additional information, or change the format in which the data is stored. To associate a value converter with a mapping, create a class that implements the IValueConverter interface and its Convert and ConvertBack methods and specify it in XAML using the Mapping.Converter property.

The data is propagated back and forth between the property, default mapping method and a data source field. You can insert a converter between the property and the default mapping method, or between default mapping method and the data source field, or instead of a default mapping method. Converter position in that propagation chain is defined by the MappingConversionBehavior enumeration.

The following image illustrates the converter’s processing order:

How to Create a Converter

The following example implements a mapping converter that returns label colors based on enumeration values:

View Example: Implement a Custom Mapping Converter for Color Values

1. Implement a class with a IValueConverter interface (inherited from the MarkupExtension class).

   PriorityToColorConverter.cs

   class PriorityToColorConverter : MarkupExtension, IValueConverter {
       public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
           if (value is Priority) {
               var priorityValue = (Priority)value;
               switch (priorityValue) {
                   case Priority.High:
                   return Colors.Red;
   
                   case Priority.Normal:
                   return Colors.Yellow;
   
                   case Priority.Low:
                   return Colors.Green;
   
                   default:
                   return Colors.Black;
               }
           }
           return Colors.Transparent;
       }
       public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
           throw new NotImplementedException();
       }
       public override object ProvideValue(IServiceProvider serviceProvider) {
           return this;
       }
   }
   

   PriorityToColorConverter.vb

   Friend Class PriorityToColorConverter
       Inherits MarkupExtension
       Implements IValueConverter
   
       Public Function Convert(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As CultureInfo) As Object Implements IValueConverter.Convert
           If TypeOf value Is Priority Then
               Dim priorityValue = CType(value, Priority)
               Select Case priorityValue
                   Case Priority.High
                       Return Colors.Red
                   Case Priority.Normal
                       Return Colors.Yellow
                   Case Priority.Low
                       Return Colors.Green
                   Case Else
                       Return Colors.Black
               End Select
           End If
   
           Return Colors.Transparent
       End Function
   
       Public Function ConvertBack(ByVal value As Object, ByVal targetType As Type, ByVal parameter As Object, ByVal culture As CultureInfo) As Object Implements IValueConverter.ConvertBack
           Throw New NotImplementedException()
       End Function
   
       Public Overrides Function ProvideValue(ByVal serviceProvider As IServiceProvider) As Object
           Return Me
       End Function
   End Class
   

2. Assign the converter to the label color mapping’s Mapping.Converter property:

   MainWindow.xaml

   <dxsch:DataSource.AppointmentLabelMappings>
       <dxsch:AppointmentLabelMappings 
           Color="{dxsch:Mapping FieldName=Id, 
                                 ConversionBehavior=BetweenFieldAndMapping, 
                                 Converter={local:PriorityToColorConverter}}"                            
           Caption="Name"
           ColorSavingType="ColorInstance"
           Id="Id"/>
   </dxsch:DataSource.AppointmentLabelMappings>