finding selected items in Telerik RadGridView using MVVM pattern

Question

I am using a Telerik RadGridView in my application and it has a GridViewSelectColumn item in it, which allows me to select various items in the grid. I have a button that operates on this selection, but am not sure how to get the list of selected items. The problem is that I am using an MVVM pattern with Caliburn.Micro. Do I need to find the control in the view and traverse the list of selected items? That seems like a lot of work for a simple task. I would appreciate any ideas.

Answer 1

The problem with Telerik's RadGridView is, that its SelectedItem collection is read-only, so you cannot bind two-way to SelectedItems.

A workaround for this is to use a custom Behavior to do the synchronization between RadGridView and your ViewModels SelectedItem collection

You may use this Behavior:

// Behavior for synchronizing a RadDataGrid's SelectedItems collection with a SelectedItems collection of the ViewModel (the Network)
// The problem is, that RadDataGrid.SelectedItems is a read-only collection and therefore cannot be used for two-way binding.

class SelectedSyncBehavior
    : Behavior<RadGridView>
{
    bool _collectionChangedSuspended = false;

    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.SelectedItems.CollectionChanged += GridSelectedItems_CollectionChanged;
    }

    /// <summary>
    /// Getter/Setter for DependencyProperty, bound to the DataContext's SelectedItems ObservableCollection
    /// </summary>
    public INotifyCollectionChanged SelectedItems
    {
        get { return (INotifyCollectionChanged)GetValue(SelectedItemsProperty); }
        set { SetValue(SelectedItemsProperty, value); }
    }

    /// <summary>
    /// Dependency Property "SelectedItems" is target of binding to DataContext's SelectedItems
    /// </summary>
    public static readonly DependencyProperty SelectedItemsProperty =
        DependencyProperty.Register("SelectedItems", typeof(INotifyCollectionChanged), typeof(SelectedSyncBehavior), new PropertyMetadata(OnSelectedItemsPropertyChanged));

    /// <summary>
    /// PropertyChanged handler for DependencyProperty "SelectedItems"
    /// </summary>
    private static void OnSelectedItemsPropertyChanged(DependencyObject target, DependencyPropertyChangedEventArgs args)
    {
        INotifyCollectionChanged collection = args.NewValue as INotifyCollectionChanged;
        if (collection != null)
        {
            // Hook to the Network's SelectedItems
            collection.CollectionChanged += (target as SelectedSyncBehavior).ContextSelectedItems_CollectionChanged;
        }
    }

    /// <summary>
    /// Will be called, when the Network's SelectedItems collection changes
    /// </summary>
    void ContextSelectedItems_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (_collectionChangedSuspended) return;    // Don't react recursively to CollectionChanged events

        _collectionChangedSuspended = true;

        // Select and unselect items in the grid
        if (e.NewItems != null)
            foreach (object item in e.NewItems)
                AssociatedObject.SelectedItems.Add(item);

        if (e.OldItems != null)
            foreach (object item in e.OldItems)
                AssociatedObject.SelectedItems.Remove(item);

        _collectionChangedSuspended = false;
    }

    /// <summary>
    /// Will be called when the GridView's SelectedItems collection changes
    /// </summary>
    void GridSelectedItems_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        if (_collectionChangedSuspended) return;    // Don't react recursively to CollectionChanged events

        _collectionChangedSuspended = true;

        // Select and unselect items in the DataContext
        if (e.NewItems != null)
            foreach (object item in e.NewItems)
                (SelectedItems as IList).Add(item);

        if (e.OldItems != null)
            foreach (object item in e.OldItems)
                (SelectedItems as IList).Remove(item);

        _collectionChangedSuspended = false;
    }

}

Use this Behavior with RadGridViews like this:

<i:Interaction.Behaviors>
   <behaviors:SelectedSyncBehavior SelectedItems="{Binding ViewModel.SelectedItems}" />
</i:Interaction.Behaviors>