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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)

public event CancelEventHandler Validating

When you change the focus by using the keyboard (TAB, SHIFT+TAB, and so on), by calling the Selector 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.


Do not attempt to set focus from within the Enter, GotFocus, Leave, LostFocus, Validating, or Validated event handlers. Doing so can cause your application or the operating system to stop responding. For more information, see the WM_KILLFOCUS topic in the "Keyboard Input Reference" section, and the "Message Deadlocks" section of the "About Messages and Message Queues" topic in the MSDN library at http://msdn.microsoft.com/library.

For more information about handling events, see Handling and Raising Events.

Legacy Code Example

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 void textBox1_Validating(object sender, 
 				System.ComponentModel.CancelEventArgs e)
   string errorMsg;
   if(!ValidEmailAddress(textBox1.Text, out errorMsg))
      // 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. 
      this.errorProvider1.SetError(textBox1, errorMsg);

private void textBox1_Validated(object sender, System.EventArgs e)
   // If all conditions have been met, clear the ErrorProvider of errors.
   errorProvider1.SetError(textBox1, "");
public bool ValidEmailAddress(string emailAddress, out string errorMessage)
   // Confirm that the e-mail address string is not empty.
   if(emailAddress.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;

.NET Framework
Available since 1.1
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