Question

I can’t seem to figure this one out by reading the documentation for ObservableCollection.Move(int oldIndex, int newIndex) on MSDN:

oldIndex Type: System.Int32 The zero-based index specifying the
location of the item to be moved. newIndex Type: System.Int32 The
zero-based index specifying the new location of the item.

I don’t understand how it works. What happens to the item with newIndex? My assumption is that the index of each item with index >= newIndex is decremented. Is that assumption correct? And more importantly, is that behavior explained or described somewhere on MSDN?

Answer 1

Let me explain the behavior of Move in a form of a unit test:

[Test]
public void ObservableTest()
{
    var observable = new ObservableCollection<string> { "A", "B", "C", "D", "E" }; 

    observable.Move(1, 3); // oldIndex < newIndex 
    // Move "B" to "D"'s place: "C" and "D" are shifted left
    CollectionAssert.AreEqual(new[] { "A", "C", "D", "B", "E" }, observable);

    observable.Move(3, 1); // oldIndex > newIndex 
    // Move "B" to "C"'s place: "C" and "D" are shifted right
    CollectionAssert.AreEqual(new[] { "A", "B", "C", "D", "E" }, observable);

    observable.Move(1, 1); // oldIndex = newIndex
    // Move "B" to "B"'s place: "nothing" happens
    CollectionAssert.AreEqual(new[] { "A", "B", "C", "D", "E" }, observable);
}