Generic List - moving an item within the list


Question

So I have a generic list, and an oldIndex and a newIndex value.

I want to move the item at oldIndex, to newIndex...as simply as possible.

Any suggestions?

Note

The item should be end up between the items at (newIndex - 1) and newIndex before it was removed.

1
137
6/25/2012 4:12:30 PM

Accepted Answer

I know you said "generic list" but you didn't specify that you needed to use the List(T) class so here is a shot at something different.

The ObservableCollection(T) class has a Move method that does exactly what you want.

public void Move(int oldIndex, int newIndex)

Underneath it is basically implemented like this.

T item = base[oldIndex];
base.RemoveItem(oldIndex);
base.InsertItem(newIndex, item);

So as you can see the swap method that others have suggested is essentially what the ObservableCollection does in it's own Move method.

UPDATE 2015-12-30: You can see the source code for the Move and MoveItem methods in corefx now for yourself without using Reflector/ILSpy since .NET is open source.

120
12/30/2015 2:09:46 PM

var item = list[oldIndex];

list.RemoveAt(oldIndex);

if (newIndex > oldIndex) newIndex--; 
// the actual index could have shifted due to the removal

list.Insert(newIndex, item);

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