wpftoolkit/ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/Core/Utilities/ValueChangeHelper.cs

/************************************************************************

   Extended WPF Toolkit

   Copyright (C) 2010-2012 Xceed Software Inc.

   This program is provided to you under the terms of the Microsoft Public
   License (Ms-PL) as published at http://wpftoolkit.codeplex.com/license 

   This program can be provided to you by Xceed Software Inc. under a
   proprietary commercial license agreement for use in non-Open Source
   projects. The commercial version of Extended WPF Toolkit also includes
   priority technical support, commercial updates, and many additional 
   useful WPF controls if you license Xceed Business Suite for WPF.

   Visit http://xceed.com and follow @datagrid on Twitter.

  **********************************************************************/

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Collections;
using System.Windows.Data;

namespace Xceed.Wpf.Toolkit.Core.Utilities
{
  /// <summary>
  /// This helper class will raise events when a specific
  /// path value on one or many items changes.
  /// </summary>
  internal class ValueChangeHelper : DependencyObject
  {

    #region Value Property
    /// <summary>
    /// This private property serves as the target of a binding that monitors the value of the binding
    /// of each item in the source.
    /// </summary>
    private static readonly DependencyProperty ValueProperty = DependencyProperty.Register( "Value", typeof( object ), typeof( ValueChangeHelper ), new UIPropertyMetadata( null, OnValueChanged ) );
    private object Value
    {
      get
      {
        return ( object )GetValue( ValueProperty );
      }
      set
      {
        SetValue( ValueProperty, value );
      }
    }

    private static void OnValueChanged( DependencyObject sender, DependencyPropertyChangedEventArgs args )
    {
      ( ( ValueChangeHelper )sender ).RaiseValueChanged();
    }
    #endregion

    public event EventHandler ValueChanged;

    #region Constructor

    public ValueChangeHelper(Action changeCallback)
    {
      if( changeCallback == null )
        throw new ArgumentNullException( "changeCallback" );

      this.ValueChanged += ( s, args ) => changeCallback();
    }

    #endregion

    #region Methods

    public void UpdateValueSource( object sourceItem, string path )
    {
      BindingBase binding = null;
      if( sourceItem != null && path != null )
      {
        binding = new Binding( path ) { Source = sourceItem };
      }

      this.UpdateBinding( binding );
    }

    public void UpdateValueSource( IEnumerable sourceItems, string path )
    {
      BindingBase binding = null;
      if( sourceItems != null && path != null )
      {
        MultiBinding multiBinding = new MultiBinding();
        multiBinding.Converter = new BlankMultiValueConverter();

        foreach( var item in sourceItems )
        {
          multiBinding.Bindings.Add( new Binding( path ) { Source = item } );
        }

        binding = multiBinding;
      }

      this.UpdateBinding( binding );
    }

    private void UpdateBinding( BindingBase binding )
    {
      if( binding != null )
      {
        BindingOperations.SetBinding( this, ValueChangeHelper.ValueProperty, binding );
      }
      else
      {
        this.ClearBinding();
      }
    }

    private void ClearBinding()
    {
      BindingOperations.ClearBinding( this, ValueChangeHelper.ValueProperty );
    }

    private void RaiseValueChanged()
    {
      if( this.ValueChanged != null )
      {
        this.ValueChanged( this, EventArgs.Empty );
      }
    }

    #endregion

    #region BlankMultiValueConverter private class

    private class BlankMultiValueConverter : IMultiValueConverter
    {
      public object Convert( object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture )
      {
        // We will not use the result anyway. We just want the change notification to kick in.
        // Return a new object to have a different value.
        return new object();
      }

      public object[] ConvertBack( object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture )
      {
        throw new InvalidOperationException();
      }
    }

    #endregion
  }
}