VB.NET - How To Extend A Custom Method to Error Provider For Field Validation

The concept is very simple, instead of coding the Error Provider Control to validate field one by one; we add custom functionality to Error Provider that can be call without creating a new derived type.

For example

From:

If String.IsNullOrEmpty(Textbox1.Text.Trim) Then

            ErrorProvider1.SetError(Textbox1, “The field cannot be empty!”)

Else

            ErrorProvider1.SetError(Textbox1,Nothing)

End If

If String.IsNullOrEmpty(Textbox2.Text.Trim) Then

            ErrorProvider1.SetError(Textbox2, “The field cannot be empty!”)

Else

            ErrorProvider1.SetError(Textbox2,Nothing)

End If

To:

ErrorProvider1.Validate(TextBox1, “This field cannot be empty!”)

ErrorProvider1.Validate(TextBox2, “This field cannot be blank!”)

If ErrorPrivider1.HasError Then

            MessageBox.Show(ErrorProvider.GetErrorMessages())

‘ Error routine here

End If

Here is my code in VB.Net:

Step one: Create a new module

Imports System.Runtime.CompilerServices

Imports System.Text

Namespace ErrorProviderExtension

            Module ErrorExtension

                       

            <Extension()> _

            Public Function Validate( ByVal Epd As ErrorProvider, _
                  ByVal Control As Control, _
                  Optional ByVal ErrorMessage As String = “Field cannot be empty!”)  As Boolean

                          If String.IsNullOrEmpty(Control.Text.Trim) Then

                                      Epd.SetError(Control, ErrorMessage)

                                      Return False

                                      Exit Function

                          End If

                                   

                          Epd.SetError(Control, Nothing)

                          Return True

             End Function

            <Extension()> _

            Public Function HasErrors(ByVal Epd As ErrorProvider) As Boolean

                        Dim err e Nullable(Of Integer) = (From e In Epd.ContainerControl.Controls _

                                                                                 Let msg = Provider.GetError(e) _

                                                                                 Where msg.Length > 0 _

                                                                                 Select e).Count

                        If err.GetValueOrDefault(0) > 0 Then

                                    Return True

                        Else

                                    Return False

                        End If

            End Function

            <Extension()> _

            Public Function GetErrorMessages(ByVal Epd As ErrorProvider) As String

                        Dim sb As New StringBuilder

                                  

                        If Epd.ContainerControl Is Nothing Then

                                    Return Nothing

                                    Exit Function

                        End If

                        Dim err = From e In Epd.ContainerControl.Controls _

                                          Let message = Epd.GetError(e) _

                                          Where message.Length > 0 _

                                          Select message

                        If Not IsNothing(err) Then

                                  Dim i As Integer = 1

                                  For Each emsg As String In err

                                            sb.AppendLine(String.Format(“{0}: {1}”, i, emsg.ToString))

                                             i += 1

                                  Next

                                  sb.AppendLine(“Please clear all the errors before continue!”)

                                  Return sb.ToString

                                  Exit Function

                       End If

                                   

                       Return Nothing

            End Function

            End Module

End Namespace

Next, create a new Windows®Form; drag an ErrorProvider, two TextBox and one Button onto it, then

Imports rootnamespace.ErrorProviderExtension

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

             ErrorProvider1.Validate(TextBox1, “TextBox1 cannot be blank!”)

             ErrorProvider1.Validate(TextBox2, “TextBox2 cannot be blank!”)

             If ErrorProvider1.HasError Then

                 MessageBox.Show(ErrorProvider1.GetErrorMessages)

                 Exit Sub

             End If

            ‘Continue here if not error

            End Sub

Note: Please refer to MSDN for supported version and methods.