Private Sub TextBox1_Validating(ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) _
Handles TextBox1.Validating

    ' If nothing is entered,
    ' an ArgumentException is caught; if an invalid directory is entered, 
    ' a DirectoryNotFoundException is caught. An appropriate error message 
    ' is displayed in either case.
    Try
        Dim directory As New System.IO.DirectoryInfo(TextBox1.Text)
        directory.GetFiles()
        ErrorProvider1.SetError(TextBox1, "")

    Catch ex1 As System.ArgumentException
        ErrorProvider1.SetError(TextBox1, "Please enter a directory")

    Catch ex2 As System.IO.DirectoryNotFoundException
        ErrorProvider1.SetError(TextBox1, _
        "The directory does not exist." & _
        "Try again with a different directory.")
    End Try

End Sub

' This method handles the LostFocus event for TextBox1 by setting the 
' dialog's InitialDirectory property to the text in TextBox1.
Private Sub TextBox1_LostFocus(ByVal sender As Object, _
    ByVal e As System.EventArgs) Handles TextBox1.LostFocus
    OpenFileDialog1.InitialDirectory = TextBox1.Text
End Sub


' This method demonstrates using the ErrorProvider.GetError method 
' to check for an error before opening the dialog box.
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click

    'If there is no error, then open the dialog box.
    If ErrorProvider1.GetError(TextBox1) = "" Then
        Dim dialogResult As DialogResult = OpenFileDialog1.ShowDialog()
    End If

End Sub

' 导入命名空间
Imports System.Windows.Forms

public class DeferredValidation
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class


Public Class Form1
    Private Sub TextBox1_Validating(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating, TextBox2.Validating, TextBox3.Validating
        If (TextBox1.Text.Length <> 0) And Not (TextBox1.Text Like "##") _
        Then
            ErrorProvider1.SetError(TextBox1, TextBox1.Name & " must contain exactly two digits")
        Else
            ErrorProvider1.SetError(TextBox1, "")
        End If

    End Sub

    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        e.Cancel = True
        If IsInvalidField(TextBox1) Then Exit Sub
        If IsInvalidField(TextBox3) Then Exit Sub
        e.Cancel = False
    End Sub

    Private Function IsInvalidField(ByVal ctl As Control) As Boolean
        If ErrorProvider1.GetError(ctl).Length = 0 Then
            Return False
        Else
            MessageBox.Show(ErrorProvider1.GetError(ctl))
            ctl.Focus()
            Return True
        End If
    End Function
End Class

<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Partial Public Class Form1
    Inherits System.Windows.Forms.Form

    'Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.components = New System.ComponentModel.Container
        Me.Label1 = New System.Windows.Forms.Label
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.TextBox2 = New System.Windows.Forms.TextBox
        Me.Label2 = New System.Windows.Forms.Label
        Me.TextBox3 = New System.Windows.Forms.TextBox
        Me.Label3 = New System.Windows.Forms.Label
        Me.ErrorProvider1 = New System.Windows.Forms.ErrorProvider(Me.components)
        CType(Me.ErrorProvider1, System.ComponentModel.ISupportInitialize).BeginInit()
        Me.SuspendLayout()
        '
        'Label1
        '
        Me.Label1.AutoSize = True
        Me.Label1.Location = New System.Drawing.Point(8, 8)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(56, 13)
        Me.Label1.TabIndex = 0
        Me.Label1.Text = "Five Digits"
        '
        'TextBox1
        '
        Me.TextBox1.Location = New System.Drawing.Point(72, 8)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(80, 20)
        Me.TextBox1.TabIndex = 1
        '
        'TextBox2
        '
        Me.TextBox2.Location = New System.Drawing.Point(72, 32)
        Me.TextBox2.Name = "TextBox2"
        Me.TextBox2.Size = New System.Drawing.Size(80, 20)
        Me.TextBox2.TabIndex = 3
        '
        'Label2
        '
        Me.Label2.AutoSize = True
        Me.Label2.Location = New System.Drawing.Point(8, 32)
        Me.Label2.Name = "Label2"
        Me.Label2.Size = New System.Drawing.Size(56, 13)
        Me.Label2.TabIndex = 2
        Me.Label2.Text = "Five Digits"
        '
        'TextBox3
        '
        Me.TextBox3.Location = New System.Drawing.Point(72, 56)
        Me.TextBox3.Name = "TextBox3"
        Me.TextBox3.Size = New System.Drawing.Size(80, 20)
        Me.TextBox3.TabIndex = 5
        '
        'Label3
        '
        Me.Label3.AutoSize = True
        Me.Label3.Location = New System.Drawing.Point(8, 56)
        Me.Label3.Name = "Label3"
        Me.Label3.Size = New System.Drawing.Size(56, 13)
        Me.Label3.TabIndex = 4
        Me.Label3.Text = "Five Digits"
        '
        'ErrorProvider1
        '
        Me.ErrorProvider1.ContainerControl = Me
        '
        'Form1
        '
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(210, 83)
        Me.Controls.Add(Me.TextBox3)
        Me.Controls.Add(Me.Label3)
        Me.Controls.Add(Me.TextBox2)
        Me.Controls.Add(Me.Label2)
        Me.Controls.Add(Me.TextBox1)
        Me.Controls.Add(Me.Label1)
        Me.Name = "Form1"
        Me.Text = "Deferred Validation"
        CType(Me.ErrorProvider1, System.ComponentModel.ISupportInitialize).EndInit()
        Me.ResumeLayout(False)
        Me.PerformLayout()

    End Sub
    Friend WithEvents Label1 As System.Windows.Forms.Label
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents TextBox2 As System.Windows.Forms.TextBox
    Friend WithEvents Label2 As System.Windows.Forms.Label
    Friend WithEvents TextBox3 As System.Windows.Forms.TextBox
    Friend WithEvents Label3 As System.Windows.Forms.Label
    Friend WithEvents ErrorProvider1 As System.Windows.Forms.ErrorProvider

End Class