Hello Valentina,

Thank you for the application details you have provided.

The Dictionary<TKey, TValue> works with KeyValuePair<Tkey, TValue> struct instances. Since the KeyValuePair is immutable (the Key and Value properties do not have setters), we cannot edit it through the XamDataGrid. This is why we will not be able to change the Value of the DataItem by using the ComboBoxField.

An approach I can suggest you in order to preserve the mappings functionality and be able to change the Value is to create a custom KeyValuePair class that has setters for its properties.
This way we can populate an ObservableCollection with the custom KeyValuePair instances and bind it to the XamDataGrid's DataSource.

public class CustomKeyValuePair<TKey, TValue>
{
    public TKey Key { get; set; }
    public TValue Value { get; set; }
    ...
}

<igDP:FieldLayout.Fields>
    <igDP:TextField Name="Key" AllowEdit="False" />
    <igDP:ComboBoxField Name="Value">
        <igDP:ComboBoxField.EditorStyle>
            <Style TargetType="igEditors:XamComboEditor">
                <Setter Property="ItemsSource" Value="{Binding Path=DataContext.Values, RelativeSource={RelativeSource AncestorType=igDP:XamDataGrid}}" />
            </Style>
        </igDP:ComboBoxField.EditorStyle>
    </igDP:ComboBoxField>
</igDP:FieldLayout.Fields>

Another approach I can suggest you is to implement a custom Dictionary and KeyValuePair, which will allow you to operate with mutable underlying instances (depending on the functionality you are looking for).

I have attached a sample application that demonstrates the initial approach from above.

If you have any questions, please let me know.