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Control.Validating Event

Occurs when the control is validating.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)

'Declaration
Public Event Validating As CancelEventHandler
'Usage
Dim instance As Control
Dim handler As CancelEventHandler

AddHandler instance.Validating, handler

/** @event */
public void add_Validating (CancelEventHandler value)

/** @event */
public void remove_Validating (CancelEventHandler value)

JScript supports the use of events, but not the declaration of new ones.

When you change the focus by using the keyboard (TAB, SHIFT+TAB, and so on), by calling the Select or SelectNextControl methods, or by setting the ContainerControl.ActiveControl property to the current form, focus events occur in the following order:

  1. Enter

  2. GotFocus

  3. Leave

  4. Validating

  5. Validated

  6. LostFocus

When you change the focus by using the mouse or by calling the Focus method, focus events occur in the following order:

  1. Enter

  2. GotFocus

  3. LostFocus

  4. Leave

  5. Validating

  6. Validated

If the CausesValidation property is set to false, the Validating and Validated events are suppressed.

If the Cancel property of the CancelEventArgs is set to true in the Validating event delegate, all events that would usually occur after the Validating event are suppressed.

For more information about handling events, see Consuming Events.

The following code example uses the derived class TextBox and validates an e-mail address that the user enters. If the e-mail address is not in the standard format (containing "@" and "."), the validation fails, an ErrorProvider icon is displayed, and the event is canceled. This example requires that a TextBox and ErrorProvider control have been created on a form.

   Private Function ValidEmailAddress(ByVal emailAddress As String, ByRef errorMessage As String) As Boolean
      ' Confirm there is text in the control.
      If textBox1.Text.Length = 0 Then
         errorMessage = "E-mail address is required."
         Return False

      End If

      ' Confirm that there is an "@" and a "." in the e-mail address, and in the correct order.
      If emailAddress.IndexOf("@") > -1 Then
         If (emailAddress.IndexOf(".", emailAddress.IndexOf("@")) > emailAddress.IndexOf("@")) Then
            errorMessage = ""
            Return True
         End If
      End If

      errorMessage = "E-mail address must be valid e-mail address format." + ControlChars.Cr + _
        "For example 'someone@example.com' "
      Return False
End Function

   Private Sub textBox1_Validating(ByVal sender As Object, _
   ByVal e As System.ComponentModel.CancelEventArgs) Handles textBox1.Validating

      Dim errorMsg As String
      If Not ValidEmailAddress(textBox1.Text, errorMsg) Then
         ' Cancel the event and select the text to be corrected by the user.
         e.Cancel = True
         textBox1.Select(0, textBox1.Text.Length)

         ' Set the ErrorProvider error with the text to display. 
         Me.errorProvider1.SetError(textBox1, errorMsg)
      End If
   End Sub


   Private Sub textBox1_Validated(ByVal sender As Object, _
   ByVal e As System.EventArgs) Handles textBox1.Validated
      ' If all conditions have been met, clear the error provider of errors.
      errorProvider1.SetError(textBox1, "")
   End Sub

private void textBox1_Validating(Object sender, 
    System.ComponentModel.CancelEventArgs e)
{
    String errorMsg = "";

    if (!(ValidEmailAddress(textBox1.get_Text(), errorMsg))) {
        // Cancel the event and select the text to be corrected by the user.
        e.set_Cancel(true);
        textBox1.Select(0, textBox1.get_Text().get_Length());

        // Set the ErrorProvider error with the text to display. 
        this.errorProvider1.SetError(textBox1, errorMsg);
    }
} //textBox1_Validating

private void textBox1_Validated(Object sender, System.EventArgs e)
{
    // If all conditions have been met, clear the ErrorProvider of errors.
    errorProvider1.SetError(textBox1, "");
} //textBox1_Validated

public boolean ValidEmailAddress(String emailAddress, 
    /** @ref 
     */ String errorMessage)
{
    // Confirm that the e-mail address string is not empty.
    if (emailAddress.get_Length() == 0) {
        errorMessage = "e-mail address is required.";
        return false;
    }

    // Confirm that there is an "@" and a "." in the e-mail address, 
    // and in the correct order.
    if (emailAddress.IndexOf("@") > -1) {
        if (emailAddress.IndexOf(".", 
            emailAddress.IndexOf("@")) > emailAddress.IndexOf("@")) {
            errorMessage = "";
            return true;
        }
    }
    errorMessage = "e-mail address must be valid e-mail address format.\n" 
        + "For example 'someone@example.com' ";
    return false;
} //ValidEmailAddress

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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