How does ObservableCollection<T>.Move(int,int) work?

问题

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?

回答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);
}

回答2:

I would go for the simple explanation:

The object is moved to the position indicated, and then all objects in collection are re-indexed from zero and up.

回答3:

Apart from great answer of @nemesv what helps me to remember the behavior is that myObservableCollection.Move(oldIndex, newIndex) is equivalent of:

var movedItem = myObservableCollection[oldIndex];
myObservableCollection.RemoveAt(oldIndex);
myObservableCollection.Insert(newIndex, movedItem);

来源：https://stackoverflow.com/questions/10471222/how-does-observablecollectiont-moveint-int-work