System.Windows.Controls.ItemContainerGenerator.CheckOffsetAndRealized C# (CSharp) Method

		void CheckOffsetAndRealized (GeneratorPosition position, int count)
		{
			if (position.Offset != 0)
				throw new ArgumentException ("position.Offset must be zero as the position must refer to a realized element");
			
			int index = IndexFromGeneratorPosition (position);
			int rangeIndex = RealizedElements.FindRangeIndexForValue (index);
			RangeCollection.Range range = RealizedElements.Ranges[rangeIndex];
			if (index < range.Start || (index + count) > range.Start + range.Count)
				throw new InvalidOperationException ("Only items which have been Realized can be removed");
		}