You cannot add a System.Windows.Forms.ListViewGroup to the collection more than once. However, attempting to add another copy will not throw an exception. Instead, the addition will simply fail. The ListViewGroupCollection.Add(ListViewGroup) method will return a value of –1 in this case. The ListViewGroupCollection.AddRange(ListViewGroup[]) and ListViewGroupCollection.Insert(int, ListViewGroup) methods, however, do not have return values. When adding groups using one of these methods, use the ListViewGroupCollection.Contains(ListViewGroup) method to determine whether a particular System.Windows.Forms.ListViewGroup is already in the collection.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
Assembly Versions: 2.0.0.0
Since: .NET 2.0