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
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.
code, to count the number of rows in an input 
, by using IO.File.ReadLines, which return Type System.Collection.Generic.IEnumerable(Of String), in 
.