Implementing Telerik VirtualQueryableCollectionView with MVVM pattern

Question

I have an application that was implemented using the Telerik RadGridView control and Caliburn.Micro MVVM framework. Because of some performance problems, I needed to implement the Telerik VirtualQueryableCollectionView in place of the direct control-to-ObservableCollection binding that was being used. The original code has the ItemsSouce property of the RadGridView was bound to the Prices property of the view model. I had to eliminate that binding and this in the code-behind:

public PricingView(PricingViewModel vm)
{
    InitializeComponent();

    var dataView = new VirtualQueryableCollectionView()
                         { LoadSize=20, VirtualItemCount = vm.Prices.Count };
    dataView.ItemsLoading += (sender, e) =>
        {
            var view = sender as VirtualQueryableCollectionView;
            if (dataView != null)
            {
                view.Load(e.StartIndex, vm.Prices.Skip(e.StartIndex).Take(e.ItemCount));
            }
        };
    this.PricesGridView.ItemsSource = dataView;
}

Since this code only deals with UI specific functionality and it is specific the the view implementation, I am comfortable that this code belongs in the code-behind rather than the ViewModel as it would be a departure from ther MVVM pattern to put a reference to VirtualQueryableCollectionView in the ViewModel. The part that I am not happy with is passing the reference to the ViewModel into the constructor of the View. Is there a good way to get the reference in the code-behind without having to pass the reference in the constructor?

Or is there a better way to do all of this?

oarrivi oarrivi · Accepted Answer · 2012-03-21T12:16:01

My application is implemented with MVVM Light, in my case I used the VirtualQueryableCollectionView class in the ViewModel instead the View.

I did so because I think this class is very similar to the ObservableCollection although it is not part of the core classes. Actually, VirtualQueryableCollectionView is not limited to the Telerik controls but many other standard controls like the ListView.

The fetch is in my case implemented in the Model.

void MainViewModel()
{
    this.Traces = new VirtualQueryableCollectionView<MyEntityClass>()
    {
        // ViewModel also manages the LoadSize
        LoadSize = this.PageSize,
        VirtualItemCount = myModel.TotalCount
    };
    this.Traces.ItemsLoading += (s, args) =>
    {
        this.Traces.Load(args.StartIndex, 
                         myModel.FetchRange(args.StartIndex, args.ItemCount));
    };
}

Implementing Telerik VirtualQueryableCollectionView with MVVM pattern

2 Answers