How to: Show Validation Errors when IDataErrorInfo is Used

• Oct 19, 2023
• 3 minutes to read

This document describes how to display validation errors in the application you created with the DevExpress Scaffolding Wizard.

Assume you have a simple entity that supports the IDataErrorInfo interface.

C#

public class Department : IDataErrorInfo {
        public int DepartmentID { get; set; }
        public string Name { get; set; }
        public decimal Budget { get; set; }
        public DateTime StartDate { get; set; }

        public string Error {
            get {
                return this["Name"] != null || this["Budget"] != null ? "Correct values" : null;
            }
        }

        public string this[string columnName] {
            get {
                switch(columnName) {
                    case "Name":
                        return string.IsNullOrEmpty(Name) ? "Name cannot be null" : null;
                    case "Budget":
                        return Budget < 0 ? "Budget cannot be negative" : null;
                    default:
                        return null;
                }
            }
        }
    }

VB.NET

Public Class Department
        Implements IDataErrorInfo

        Public Property DepartmentID() As Integer
        Public Property Name() As String
        Public Property Budget() As Decimal
        Public Property StartDate() As Date

        Public ReadOnly Property [Error]() As String
            Get
                Return If(Me("Name") IsNot Nothing OrElse Me("Budget") IsNot Nothing, "Correct values", Nothing)
            End Get
        End Property

        Default Public ReadOnly Property Item(ByVal columnName As String) As String
            Get
                Select Case columnName
                    Case "Name"
                        Return If(String.IsNullOrEmpty(Name), "Name cannot be null", Nothing)
                    Case "Budget"
                        Return If(Budget < 0, "Budget cannot be negative", Nothing)
                    Case Else
                        Return Nothing
                End Select
            End Get
        End Property
    End Class

First, generate an application using the Scaffolding Wizard as described in the first lesson of the following tutorial: Building Office-Inspired Applications.

To display data items, the Scaffolding Wizard generates DataLayoutItem objects that, in turn, generate editors in runtime.

XAML

<dxlc:DataLayoutItem Label="Name" Name="layoutItemName" Binding="{Binding Name, UpdateSourceTrigger=PropertyChanged}" />

After completing the initial steps, validation errors will be displayed in the following manner.

In most cases, saving the changes to a database should be prohibited if the entity supports the IDataErrorInfo interface and there data errors in the entity. The generated application supports this scenario out of the box. If you want to allow the end user save changes even if there data errors or implement your own validation logic, override the HasValidationErrors method generated by the Scaffolding Wizard.

C#

partial class SingleObjectViewModel<TEntity, TPrimaryKey, TUnitOfWork> {
        protected override bool HasValidationErrors() {
            return false;
        }
    }

VB.NET

Partial Friend Class SingleObjectViewModel(Of TEntity, TPrimaryKey, TUnitOfWork)
        Protected Overrides Function HasValidationErrors() As Boolean
            Return False
        End Function
    End Class

If the HasValidationErrors method returns true, the Save button will be disabled. Additionally, when pressing the Close button, a modal warning dialog will appear with only two buttons: OK and Cancel.