The WPF Grid and TreeList controls support DataAnnotations attributes that specify data validation rules (to use data annotation attributes, reference the System.ComponentModel.DataAnnotations assembly).
By default, the grid (or treelist) displays error icons (
) within cells with invalid values, and provides error descriptions displayed as tooltips (see the image below). In this case, the cell focus cannot be moved to another cell until the cell's value is corrected.

To override the default behavior and hide errors, set the ShowValidationAttributeErrors property to false. If the ShowValidationAttributeErrors property is set to DevExpress.Utils.DefaultBoolean.Default, the visibility of error icons is specified by the view's DataViewBase.ShowValidationAttributeErrors property. In this case, use the ActualShowValidationAttributeErrors property to obtain whether validation errors are allowed to be displayed within column cells.
To learn more, see Attributes-Based Validation.