/lambλda/calculus/

This is kind of an edge case, but it just stole about two hours of my day, so I thought it might be of interest for someone else who stumbles upon this problem.

In the application I am currently working on I am subclassing a ListView to make it handle strongly typed tags, and for example directly get a strongly typed instance of the tag of the currently selected item. To test my implementation I programmatically created an instance of my ListView subclass, added items and added an item to the selection using both:

Item.Selected = true

and

listView.SelectedIndices.Add(...)

The problem was that this had no effect at all on the ListView\'s SelectedIndices and SelectedItems collections.

I tried doing the same thing on a ListView in one of the forms of my appliation and that worked, but it did not work if I instantiated the ListView directly in the code. After some googeling I finally found a comment to the MSDN documentation on the ListViewItem.Selected Property, saying that the Selected property could not be trusted if the ListView had not been drawn. I did some quick testing myself and confirmed that the problem indeed disappeared if the ListView was drawn.

So, the solution to the problem was to do something like this:

        [Test]
        public void CanGetSelectedItems()
        {
            // Sadly, this is needed to make the ListView handle selection properly.
            // If the ListView is instantiated directly SelectedIndices, SelectedItems etc
            // do not update when modified.
            var f = new DummyForm(listView);
            f.Show();
            listView.SelectedIndices.Add(0);
            Assert.AreEqual(1, listView.SelectedIndices.Count);
            ICollection<string> items = listView.SelectedItems;
            Assert.AreEqual(1, items.Count);
            Assert.IsTrue(items.Contains(strings[0]));
        }
        private class DummyForm : Form
        {
            public DummyForm(ListView listView)
            {
                this.WindowState = FormWindowState.Minimized;
                this.ShowInTaskbar = false;
                this.Controls.Add(listView);
            }
        }