Click here to Skip to main content
Click here to Skip to main content
Technical Blog

Tagged as

Binding to the selected items of a ListBox (or another items controls)

, 14 Jun 2010 Ms-PL
Rate this:
Please Sign up or sign in to vote.
A problem you often meet when using MVVM is to get the selected items of an items control, especially Listbox.

A problem you often meet when using MVVM is to get the selected items of an items control, especially Listbox.

You can easily bind the selected item or the current items but when multi selection comes in the way, it becomes harder because the SelectedItems (with an 's' property is not available to binding).

In this article, we will discover an easy way to bind yourself with an attached property to the SelectedItems property of the ListBox control.

We will use the Ramora pattern discussed before to bind ourself to the ListBox's selectionChanged events and then update the target list when the selection change.

If the target list implements INotifyCollectionChanged, we will update the listbox selection when this event is raised. Here is the resulting code:

public class ListBoxSelectedItemsSyncher : DependencyObject
{
  private static List<Syncher> _synchers = new List<Syncher>();
 
  #region ListToSync
 
  /// <span class="code-SummaryComment"><summary>
</span>  /// ListToSync Attached Dependency Property
  /// <span class="code-SummaryComment"></summary>
</span>  public static readonly DependencyProperty ListToSyncProperty =
    DependencyProperty.RegisterAttached("ListToSync", 
	             typeof(IList), typeof(ListBoxSelectedItemsSyncher),
      new FrameworkPropertyMetadata((IList)new List<Object>(),
        FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, 
		       new PropertyChangedCallback(OnListToSyncChanged)));

  private static void OnListToSyncChanged(DependencyObject d, 
    DependencyPropertyChangedEventArgs e)
  {
    ListBox listBox = d as ListBox;

    if(!(d is ListBox)
     throw new ArgumentException(
       "ListBoxSelectedItemsSyncher is only applyable to Listbox");

    Syncher synch = (from Syncher syncher 
	              in _synchers where syncher.ListBox == listBox select syncher)
                             .FirstOrDefault();
    if (synch != null)
    {
      synch.ListToSync = e.NewValue as IList;
    } else
    {
      synch = new Syncher(listBox, e.NewValue as IList);
      _synchers.Add(synch);
      listBox.Unloaded += new RoutedEventHandler(listBox_Unloaded);
    }
  }
 
  static void listBox_Unloaded(object sender, RoutedEventArgs e)
  {
    ListBox listBox = sender as ListBox;
    Syncher synch = (from Syncher syncher 
	              in _synchers where syncher.ListBox == listBox select syncher)
                      .FirstOrDefault();
    if (synch != null)
    {
      _synchers.Remove(synch);
      synch.Dispose();
      synch = null;
    }
  }
 
  /// <span class="code-SummaryComment"><summary>
</span>  /// Gets the ListToSync property.  This dependency property 
  /// indicates ....
  /// <span class="code-SummaryComment"></summary>
</span>  public static IList GetListToSync(DependencyObject d)
  {
    return (IList)d.GetValue(ListToSyncProperty);
  }
 
  /// <span class="code-SummaryComment"><summary>
</span>  /// Sets the ListToSync property.  This dependency property 
  /// indicates ....
  /// <span class="code-SummaryComment"></summary>
</span>  public static void SetListToSync(DependencyObject d, IList value)
  {
    d.SetValue(ListToSyncProperty, value);
  }
 
  #endregion
 
 
  internal class Syncher : IDisposable
  {
 
    private ListBox _listbox;
    public ListBox ListBox { get { return _listbox; } }
 
    private IList _listToSync;
    public IList ListToSync
    {
      get { return _listToSync; }
 
      set
      {
        detachTheListToSynch();
        _listToSync = value;
        attachTheListToSynch();
      }
    }
 
    public Syncher(ListBox listbox, IList listToSync)
    {
      _listbox = listbox;
      _listToSync = listToSync;
      attachTheListToSynch();
    }
 
    void collectionChangedList_CollectionChanged(object sender,
                        	NotifyCollectionChangedEventArgs e)
    {
      //Add new items   
      if (e.NewItems != null)
      {
        foreach (Object item in e.NewItems)
        {
          _listbox.SelectedItems.Add(item);
        }
      }
      if (e.OldItems != null)
      {
        foreach (Object item in e.OldItems)
        {
          _listbox.SelectedItems.Remove(item);
        }
      }
 
      if (e.Action == NotifyCollectionChangedAction.Reset)
        _listbox.SelectedItems.Clear();
 
      CommandManager.InvalidateRequerySuggested();
    }
 
    void _list_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
      if (_listToSync != null)
      {
        //Add new items                   
        foreach (Object item in e.AddedItems)
        {
          _listToSync.Add(item);
        }
        foreach (Object item in e.RemovedItems)
        {
          _listToSync.Remove(item);
        }
        CommandManager.InvalidateRequerySuggested();
      }
    }
 
    #region IDisposable Members
    public void Dispose()
    {
      if (_listbox == null) return;
      _listbox.SelectionChanged -= _list_SelectionChanged;
      detachTheListToSynch();
      _listbox = null;
    }
    #endregion
 
    #region private methods
    private void attachTheListToSynch()
    {
      _listbox.SelectionChanged -= _list_SelectionChanged;
      if (_listToSync == null) return;
 
      INotifyCollectionChanged collectionChangedList = null;
      if ((collectionChangedList = _listToSync as INotifyCollectionChanged) != null)
        collectionChangedList.CollectionChanged 
	  += new NotifyCollectionChangedEventHandler(
           collectionChangedList_CollectionChanged);
 
      //Update the selection with the new list
      _listbox.SelectedItems.Clear();
 
      foreach (var item in _listToSync)
        _listbox.SelectedItems.Add(item);
 
      _listbox.SelectionChanged 
	       += new SelectionChangedEventHandler(_list_SelectionChanged);
    }
 
    private void detachTheListToSynch()
    {
      INotifyCollectionChanged collectionChangedList = null;
      if ((collectionChangedList = _listToSync as INotifyCollectionChanged) != null)
        collectionChangedList.CollectionChanged -= 
        collectionChangedList_CollectionChanged;
    }
    #endregion
 
  }
 }

Here we are.
Edit: I found out later another version of the same feature made by Samuel Jack on his blog: http://blog.functionalfun.net/2009/02/how-to-databind-to-selecteditems.html !

License

This article, along with any associated source code and files, is licensed under The Microsoft Public License (Ms-PL)

Share

About the Author

jmix90
Software Developer http://wpf-france.fr
France (Metropolitan) France (Metropolitan)
Jonathan creates software, mostly with C#,WPF and XAML.

He really likes to works on every Natural User Interfaces(NUI : multitouch, touchless, etc...) issues.



He is awarded Microsoft MVP in the "Client Application Development" section since 2011.
 

You can check out his WPF/C#/NUI/3D blog http://www.jonathanantoine.com.

He is also the creator of the WPF French community web site : http://wpf-france.fr.

Here is some videos of the projects he has already work on :
Follow on   Twitter

Comments and Discussions

 
QuestionWhat's with all the URL's in your code? Pinmembertonyt14-Jun-10 9:37 
AnswerRe: What's with all the URL's in your code? Pinmemberjmix9014-Jun-10 12:55 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Terms of Use | Mobile
Web02 | 2.8.150129.1 | Last Updated 14 Jun 2010
Article Copyright 2010 by jmix90
Everything else Copyright © CodeProject, 1999-2015
Layout: fixed | fluid