The StartUpdateLink/EndUpdateLink methods record and add changes of the current link to the control's Undo/Redo queue. You can use the StartBlockUndoRedo / EndBlockUndoRedo methods to group multiple Undo/Redo operations into a single-block. The AllowUndoRedo property specifies whether the control supports undo/redo operations for objects (links, links, ...). No entry is added to the Undo/Redo queue if no property is changed for the current link. Each call of the StartUpdateLink must be succeeded by a EndUpdateLink call. The UndoListAction property lists the Undo actions that can be performed in the chart. The RedoListAction property lists the Redo actions that can be performed in the chart.

The StartUpdateLink/EndUpdateLink methods can record changes for the following properties only:

• ElementFrom, specifies the element where the link starts from
• ElementTo, specifies the element where the link ends into
• ID, specifies the link's unique identifier
• Style, specifies the link's style
• Color, specifies the link's color
• Width, specifies the link's width
• Visible, shows or hides the link
• StartPos, specifies where the link starts on the source/from element
• EndPos, specifies where the link ends on the target/to element
• ShowLinkType, specifies how the link shows from source to target element
• ShowDir, shows or hides the link's direction/arrow
• ArrowColor, defines the link's arrow color
• UserData, associates any extra data associated with the link
• Caption, gets or sets a value that indicates the HTML caption to be displayed on the link
• ToolTip, gets or sets a value (tooltip) that's displayed once the cursor hovers the link
• ToolTipTitle, gets or sets a value (title) that's displayed once the cursor hovers the link
• AllowControlPoint, indicates the control points of the link, the user can use to customize the link
• CustomPath, specifies the link's custom path

The Undo/Redo records show as:

• "UpdateLink;LINKID", indicates that one or more properties of the element has been updated, using the StartUpdateLink / EndUpdateLink methods

within the UndoListAction/RedoListAction result