So far we have discussed how to create outlines with trees and totals using the high-level Subtotal method as well as lower-level Rows.InsertNode and Aggregate methods.

At this point, it is important to remember that the outline tree is created based on the data, but is not bound to it in any way, and is not automatically maintained when there are changes to the grid or to the data.

If the user modifies a value in the "ExtendedPrice" column, for example, the subtotals will not be automatically updated. If the user sorts the grid, the data will be refreshed and the subtotals will disappear.

There are two common ways to maintain the outlines:

1. Prevent the user from making any changes that would invalidate the outline. This is the easiest option. You would set the grid's AllowEditing, AllowDragging, and AllowSorting properties to false and prevent any changes that would affect the outline.
2. Update the outline when there are changes to the data or to the grid. You would attach handlers to the grid's AfterDataRefresh, AfterSort, and AfterEdit events and re-generate the outline appropriately.

Option 2 is usually more interesting since it provides a quick and simple tool for dynamic data analysis. This approach is illustrated by the Analyze sample provided with the C1FlexGrid. The sample creates an initial outline and allows users to reorder the columns. When the column order changes, the sample automatically re-sorts the data and re-creates the outline. The user can easily create simple reports showing sales by country, by product, by salesperson, and so on.