This property differs from the Control.ID property, in that the Control.UniqueID property includes the identifier for the server control's naming container. This identifier is generated automatically when a page request is processed.

This property is particularly important in differentiating server controls contained within a data-binding server control that repeats. The repeating control, which are System.Web.UI.WebControls.Repeater, System.Web.UI.WebControls.DataList, System.Web.UI.WebControls.DetailsView, System.Web.UI.WebControls.FormView, and System.Web.UI.WebControls.GridView Web server controls (or any custom server controls that you create that include repeating functionality when data bound), serves as the naming container for its child controls. This means that it creates a unique namespace for its child controls so that their Control.ID property values do not conflict.

For example, if you include an ASP.NET System.Web.UI.WebControls.Label Web server control in a System.Web.UI.WebControls.Repeater server control, and assign the System.Web.UI.WebControls.Label control an Control.ID property value of MyLabel, and the System.Web.UI.WebControls.Repeater an Control.ID of MyRepeater. If you bind data to the System.Web.UI.WebControls.Repeater to an ArrayList object with three entries, the resulting Control.UniqueID properties for each instance of the System.Web.UI.WebControls.Label server controls are MyRepeater$ctl00$MyLabel, MyRepeater$ctl01$MyLabel, and MyRepeater$ctl02$MyLabel.