Unit testing VirtualQueryableCollectionView

[Kjetil]

Is it possible to write unit test against the VirtualQueryableCollectionView? I tried to write a unit test to verify the VirtualItemCount, but it seems that the collection is tightly coupled to the UI components and therefore requires tests to run on a STA thread. Is this correct?

[Vlad]

Hello,

 Generally VirtualQueryableCollectionView is not coupled with any UI component and our own tests are plain unit tests. For example:

        [TestMethod]
        public void IListIndexer_ShouldCallItemsLoading()
        {
            virtualQueryableCollectionViewWithSource.VirtualItemCount = 10;
            virtualQueryableCollectionViewWithSource.LoadSize = 2;

            bool ItemsLoadingRaised = false;

            virtualQueryableCollectionViewWithSource.ItemsLoading += (s, e) => 
            {
                ItemsLoadingRaised = true;
            };

            var firstItem = ((IList)virtualQueryableCollectionViewWithSource)[0];

            Assert.AreEqual(true, ItemsLoadingRaised);
        }

Regards,
Vlad
the Telerik team

[Kjetil]

Then why do I get the following stack trace and exception when I set the VirtualItemCount;

System.InvalidOperationException : The calling thread must be STA, because many UI components require this.

at System.Windows.Input.InputManager..ctor()

at System.Windows.Input.InputManager.GetCurrentInputManagerImpl()

at System.Windows.Input.KeyboardNavigation..ctor()

at System.Windows.FrameworkElement.FrameworkServices..ctor()

at System.Windows.FrameworkElement.EnsureFrameworkServices()

at System.Windows.FrameworkElement..ctor()

at System.Windows.Controls.Control..ctor()

at Telerik.Windows.Controls.Design.Designer.get_IsInDesignMode()

at Telerik.Windows.Data.VirtualQueryableCollectionView.Dispatcher.BeginInvoke(Action action)

at Telerik.Windows.Data.VirtualQueryableCollectionView.RefreshSource()

at Telerik.Windows.Data.VirtualQueryableCollectionView.set_VirtualItemCount(Int32 value)

[Vlad]

Hi,

 I'm afraid that we are out of ideas what is causing this exception at your end. 

Kind regards,
Vlad
the Telerik team

[Kjetil]

Shouldn't be hard to reproduce though. Here's a test that gives the InvalidOperationException;

using NUnit.Framework;
using Telerik.Windows.Data;

namespace TelerikTester
{
    [TestFixture]
    public class VirtualQueryableCollectionViewTester
    {
        [Test]
        public void Should_load_items_when_count_has_changed()
        {
            var viewModel = new ViewModel();
            bool itemsLoaded = false;
            viewModel.Items.ItemsLoading += (sender, args) => itemsLoaded = true;

            viewModel.Items.VirtualItemCount = 0;
            viewModel.Items.VirtualItemCount = 1;

            Assert.That(itemsLoaded, Is.True);
        }
    }

    public class ViewModel
    {
        public VirtualQueryableCollectionView<object> Items { get; set; }

        public ViewModel()
        {
            Items = new VirtualQueryableCollectionView<object>();
        }
    }
}

[Vlad]

Hello,

 I've tried your test however the test just failed - no exceptions. I've attached screenshot for reference. I'm not using NUnit however - maybe this is causing the difference. 

Greetings,
Vlad
the Telerik team

[Kjetil]

I'm guessing you don't get the exception because the MSTestrunner is running in a STA Thread. However, shouldn't the test suceed in this case? Shouldn't the ItemsLoading event be triggered when VirtualItemCount is set?

If you run the tests with a testrunner that runs in MTA mode, e.g. the R# testrunner or NCrunch, you will get the exception.

[Vlad]

Hello,

 ItemsLoading will be raised only if you try to access some item by index and this item is not yet loaded. 

Greetings,
Vlad
the Telerik team