How to: Create the Field Value Template

using DevExpress.Xpf.PivotGrid;
using HowToCreateFieldValueTemplate.CategoryPicturesTableAdapters;
using System;
using System.Collections.Generic;
using System.IO;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Imaging;

namespace HowToCreateFieldValueTemplate
{
    public class CategoriesControl : Control, IWeakEventListener {

        #region static staff
        static CategoriesTableAdapter categoriesTableAdapter;
        static Dictionary<string, ImageSource> categoriesPictures;
        public static readonly DependencyProperty ImageSourceProperty;

        static CategoriesControl() {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(CategoriesControl), 
                new FrameworkPropertyMetadata(typeof(CategoriesControl)));
            Type ownerType = typeof(CategoriesControl);
            ImageSourceProperty = DependencyProperty.Register("ImageSource", typeof(ImageSource),
                   ownerType, new UIPropertyMetadata());
            categoriesPictures = new Dictionary<string, ImageSource>();
        }

        static CategoriesTableAdapter CategoriesTableAdapter {
            get {
                if(categoriesTableAdapter == null)
                    categoriesTableAdapter = new CategoriesTableAdapter();
                return categoriesTableAdapter;
            }
        }

        static ImageSource GetImage(string categoryName) {
            if(string.IsNullOrEmpty(categoryName)) return null;
            if(categoriesPictures.ContainsKey(categoryName)) {
                return categoriesPictures[categoryName];
            } else {
                byte[] icon = CategoriesTableAdapter.GetIconImageByName(categoryName) as byte[];
                if(icon == null || icon.Length == 0) {
                    return null;
                }
                BitmapDecoder img = new PngBitmapDecoder(new MemoryStream(icon), 
                    BitmapCreateOptions.None, 
                    BitmapCacheOption.OnLoad);
                ImageSource imageSource = img.Frames[0];
                if(imageSource.Height < 1) return null;
                categoriesPictures.Add(categoryName, imageSource);
                return imageSource;
            }
        }

        #endregion

        public CategoriesControl()
            : base() {
            FrameworkElementDataContextChangedEventManager.AddListener(this, this);
            Unloaded += OnUnloaded;
        }

        public ImageSource ImageSource {
            get { return (ImageSource)GetValue(ImageSourceProperty); }
            set { SetValue(ImageSourceProperty, value); }
        }

        void OnUnloaded(object sender, RoutedEventArgs e) {
            ImageSource = null;
        }
        void OnDataContextChanged() {
            SetImageSource();
        }
        void SetImageSource() {
            FieldValueElementData item = this.DataContext as FieldValueElementData;
            if(item != null && !item.IsOthersRow && !string.IsNullOrEmpty(item.DisplayText)) {
                ImageSource = CategoriesControl.GetImage(item.Value as string);
            } else {
                ImageSource = null;
            }
        }

        #region IWeakEventListener Members
        bool IWeakEventListener.ReceiveWeakEvent(Type managerType, object sender, EventArgs e) {
            return OnReceiveWeakEvent(managerType, e);
        }
        protected virtual bool OnReceiveWeakEvent(Type managerType, EventArgs e) {
            if(managerType == typeof(FrameworkElementDataContextChangedEventManager)) {
                OnDataContextChanged();
                return true;
            }
            return false;
        }
        #endregion

        #region FrameworkElementDataContextChangedEventManager

        public class FrameworkElementDataContextChangedEventManager : WeakEventManager {
            static FrameworkElementDataContextChangedEventManager CurrentManager {
                get {
                    Type managerType = typeof(FrameworkElementDataContextChangedEventManager);
                    FrameworkElementDataContextChangedEventManager currentManager =
                        (FrameworkElementDataContextChangedEventManager)WeakEventManager
                        .GetCurrentManager(managerType);
                    if(currentManager == null) {
                        currentManager = new FrameworkElementDataContextChangedEventManager();
                        WeakEventManager.SetCurrentManager(managerType, currentManager);
                    }
                    return currentManager;
                }
            }

            FrameworkElementDataContextChangedEventManager() { }

            public static void AddListener(FrameworkElement source, IWeakEventListener listener) {
                CurrentManager.ProtectedAddListener(source, listener);
            }
            public static void RemoveListener(FrameworkElement source, IWeakEventListener listener) {
                CurrentManager.ProtectedRemoveListener(source, listener);
            }
            protected override void StartListening(object source) {
                FrameworkElement FrameworkElement = (FrameworkElement)source;
                FrameworkElement.DataContextChanged += OnDataContextChanged;
            }
            protected override void StopListening(object source) {
                FrameworkElement FrameworkElement = (FrameworkElement)source;
                FrameworkElement.DataContextChanged -= OnDataContextChanged;
            }
            void OnDataContextChanged(object sender, DependencyPropertyChangedEventArgs e) {
                base.DeliverEvent(sender, null);
            }
        }
        #endregion
    }
}

?Imports DevExpress.Xpf.PivotGrid
Imports HowToCreateFieldValueTemplate.CategoryPicturesTableAdapters
Imports System
Imports System.Collections.Generic
Imports System.IO
Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Media
Imports System.Windows.Media.Imaging

Namespace HowToCreateFieldValueTemplate
    Public Class CategoriesControl
        Inherits Control
        Implements IWeakEventListener

        #Region "static staff" 

        Private Shared categoriesTableAdapter_Renamed As CategoriesTableAdapter
        Private Shared categoriesPictures As Dictionary(Of String, ImageSource)
        Public Shared ReadOnly ImageSourceProperty As DependencyProperty

        Shared Sub New()
            DefaultStyleKeyProperty.OverrideMetadata(GetType(CategoriesControl), New FrameworkPropertyMetadata(GetType(CategoriesControl)))
            Dim ownerType As Type = GetType(CategoriesControl)
            ImageSourceProperty = DependencyProperty.Register("ImageSource", GetType(ImageSource), ownerType, New UIPropertyMetadata())
            categoriesPictures = New Dictionary(Of String, ImageSource)()
        End Sub 

        Private Shared ReadOnly Property CategoriesTableAdapter() As CategoriesTableAdapter
            Get 
                If categoriesTableAdapter_Renamed Is Nothing Then 
                    categoriesTableAdapter_Renamed = New CategoriesTableAdapter()
                End If 
                Return categoriesTableAdapter_Renamed
            End Get 
        End Property 

        Private Shared Function GetImage(ByVal categoryName As String) As ImageSource
            If String.IsNullOrEmpty(categoryName) Then 
                Return Nothing 
            End If 
            If categoriesPictures.ContainsKey(categoryName) Then 
                Return categoriesPictures(categoryName)
            Else 
                Dim icon() As Byte = TryCast(HowToCreateFieldValueTemplate.CategoryPicturesTableAdapters.CategoriesTableAdapter.GetIconImageByName(categoryName), Byte())
                If icon Is Nothing OrElse icon.Length = 0 Then 
                    Return Nothing 
                End If 
                Dim img As BitmapDecoder = New PngBitmapDecoder(New MemoryStream(icon), BitmapCreateOptions.None, BitmapCacheOption.OnLoad)

                Dim imageSource_Renamed As ImageSource = img.Frames(0)
                If imageSource_Renamed.Height < 1 Then 
                    Return Nothing 
                End If 
                categoriesPictures.Add(categoryName, imageSource_Renamed)
                Return imageSource_Renamed
            End If 
        End Function 

        #EndRegion

        Public Sub New()
            MyBase.New()
            FrameworkElementDataContextChangedEventManager.AddListener(Me, Me)
            AddHandler Unloaded, AddressOf OnUnloaded
        End Sub 

        Public Property ImageSource() As ImageSource
            Get 
                Return DirectCast(GetValue(ImageSourceProperty), ImageSource)
            End Get 
            Set(ByVal value As ImageSource)
                SetValue(ImageSourceProperty, value)
            End Set 
        End Property 

        Private Sub OnUnloaded(ByVal sender As Object, ByVal e As RoutedEventArgs)
            ImageSource = Nothing 
        End Sub 
        Private Sub OnDataContextChanged()
            SetImageSource()
        End Sub 
        Private Sub SetImageSource()
            Dim item As FieldValueElementData = TryCast(Me.DataContext, FieldValueElementData)
            If item IsNot Nothing AndAlso Not item.IsOthersRow AndAlso Not String.IsNullOrEmpty(item.DisplayText) Then 
                ImageSource = CategoriesControl.GetImage(TryCast(item.Value, String))
            Else 
                ImageSource = Nothing 
            End If 
        End Sub 

        #Region "IWeakEventListener Members" 
        Private Function IWeakEventListener_ReceiveWeakEvent(ByVal managerType As Type, ByVal sender As Object, ByVal e As EventArgs) As Boolean Implements IWeakEventListener.ReceiveWeakEvent
            Return OnReceiveWeakEvent(managerType, e)
        End Function 
        Protected Overridable Function OnReceiveWeakEvent(ByVal managerType As Type, ByVal e As EventArgs) As Boolean 
            If managerType Is GetType(FrameworkElementDataContextChangedEventManager) Then 
                OnDataContextChanged()
                Return True 
            End If 
            Return False 
        End Function 
        #EndRegion

        #Region "FrameworkElementDataContextChangedEventManager" 

        Public Class FrameworkElementDataContextChangedEventManager
            Inherits WeakEventManager

            Private Shared ReadOnly Property CurrentManager() As FrameworkElementDataContextChangedEventManager
                Get 
                    Dim managerType As Type = GetType(FrameworkElementDataContextChangedEventManager)

                    Dim currentManager_Renamed As FrameworkElementDataContextChangedEventManager = CType(WeakEventManager.GetCurrentManager(managerType), FrameworkElementDataContextChangedEventManager)
                    If currentManager_Renamed Is Nothing Then 
                        currentManager_Renamed = New FrameworkElementDataContextChangedEventManager()
                        WeakEventManager.SetCurrentManager(managerType, currentManager_Renamed)
                    End If 
                    Return currentManager_Renamed
                End Get 
            End Property 

            Private Sub New()
            End Sub 

            Public Shared Sub AddListener(ByVal source As FrameworkElement, ByVal listener As IWeakEventListener)
                CurrentManager.ProtectedAddListener(source, listener)
            End Sub 
            Public Shared Sub RemoveListener(ByVal source As FrameworkElement, ByVal listener As IWeakEventListener)
                CurrentManager.ProtectedRemoveListener(source, listener)
            End Sub 
            Protected Overrides Sub StartListening(ByVal source As Object)
                Dim FrameworkElement As FrameworkElement = DirectCast(source, FrameworkElement)
                AddHandler FrameworkElement.DataContextChanged, AddressOf OnDataContextChanged
            End Sub 
            Protected Overrides Sub StopListening(ByVal source As Object)
                Dim FrameworkElement As FrameworkElement = DirectCast(source, FrameworkElement)
                RemoveHandler FrameworkElement.DataContextChanged, AddressOf OnDataContextChanged
            End Sub 
            Private Sub OnDataContextChanged(ByVal sender As Object, ByVal e As DependencyPropertyChangedEventArgs)
                MyBase.DeliverEvent(sender, Nothing)
            End Sub 
        End Class 
        #EndRegion
    End Class 
End Namespace 

<Window x:Class="HowToCreateFieldValueTemplate.MainWindow" 
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
        xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors" 
        xmlns:dxpg="http://schemas.devexpress.com/winfx/2008/xaml/pivotgrid" 
        xmlns:example="clr-namespace:HowToCreateFieldValueTemplate" 
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
        Title="MainWindow" Height="350" Width="525" Loaded="Window_Loaded" >
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="CategoriesControl.xaml" />
            </ResourceDictionary.MergedDictionaries>
            <DataTemplate x:Key="ProductsTemplate" >
                <example:CategoriesControl />
            </DataTemplate>
        </ResourceDictionary>
    </Window.Resources>
    <Grid>
        <dxpg:PivotGridControl HorizontalAlignment="Left" Name="pivotGridControl1" 
                               VerticalAlignment="Top">
            <dxpg:PivotGridControl.Fields>
                <dxpg:PivotGridField Name="fieldCountry" FieldName="Country" Area="ColumnArea" />
                <dxpg:PivotGridField Name="fieldCustomer" FieldName="Sales Person" Area="ColumnArea" 
                                     Caption="Customer" />
                <dxpg:PivotGridField Name="fieldYear" FieldName="OrderDate" Area="RowArea" 
                                     Caption="Year" GroupInterval="DateYear" />
                <dxpg:PivotGridField Name="fieldCategoryName" FieldName="CategoryName" Area="RowArea" 
                                     ValueTemplate="{StaticResource  ResourceKey=ProductsTemplate}" 
                                     Caption="Product Category"/>
                <dxpg:PivotGridField Name="fieldExtendedPrice" FieldName="Extended Price" 
                                     Area="DataArea" CellFormat="c0" />
            </dxpg:PivotGridControl.Fields>
        </dxpg:PivotGridControl>
    </Grid>
</Window>