Typically, you specify a value for the SupportsPreviewControlAttribute.SupportsPreviewControl property by applying the System.Web.UI.Design.SupportsPreviewControlAttribute attribute to a custom designer class declaration. The value of the SupportsPreviewControlAttribute.SupportsPreviewControl property for the System.Web.UI.Design.SupportsPreviewControlAttribute attribute determines the behavior for the ControlDesigner.UsePreviewControl and ControlDesigner.ViewControl members in the base System.Web.UI.Design.ControlDesigner class.

Set the SupportsPreviewControlAttribute.SupportsPreviewControl property to true to indicate that the designer uses a temporary copy of the associated control to generate the design-time HTML. Changes to the temporary control are not persisted.

Set the SupportsPreviewControlAttribute.SupportsPreviewControl property to false to indicate that the designer returns the control instance, specifically the System.ComponentModel.Design.ComponentDesigner.Component property, from the ControlDesigner.ViewControl method. Changes to the control object are persisted.