How to do validation in textbox in vb.net
Say you have a textbox
Private Function isValidEmailAddress(ByVal emailAddress As String) As Boolean
' Confirm there is text in the control.
If emailAddress.Length = 0 Then Return False
' Confirm that there is an "@" and a "."
' Obviously this can be much better validation
Dim atIndex As Integer = emailAddress.IndexOf("@")
If atIndex > -1 Then
If (emailAddress.IndexOf(".", atIndex) > atIndex) Then Return True
Private Sub TextBox1_Validating(ByVal sender As Object, _
ByVal e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
If Not ValidEmailAddress(TextBox1.Text.Trim) Then
' Cancel the event and select the text to be corrected by the user.
e.Cancel = True
' Set the ErrorProvider error with the text to display.
Me.ErrorProvider1.SetError(TextBox1, "You must enter a valid email address")
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.
You may be interested in the order events fire on the TextBox:
Enter, GotFocus, Leave, Validating, Validated, LostFocus
Enter, GotFocus, LostFocus, Leave, Validating, Validated
Using the ErrorProvider (just drag one onto your form from the toolbox) will greatly ease the displaying of errors. This automatically shows the user what to do (based on your message to the ErrorProvider). It will also disable all the other controls - but ONLY if they have CausesValidation=true. So even if you aren't going to validate a textbox, if you want it disabled when something else isn't valid, make sure you leave CausesValidation set to True (default).
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