VB.NET validate the form to check if empty fields or errors exists

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So far I have written code to remain Save and Update buttons disabled until user fills all required fields(Textboxes, Comboboxes) in Groupbox, but I also want the Save and Update buttons to remain disabled until user has addressed all errors available in the form e.g txtISBN.text should not go beyond 13 characters!

I would really appreciate if someone help me in this!

Below is the code that I tried to do so what I have mentioned above but somehow it is not working

VB

Private Sub btnInsert_Click(sender As Object, e As EventArgs) Handles btnInsert.Click
'creating a FOR EACH LOOP to check all textboxes for value presence
        For Each t As TextBox In GroupBox1.Controls.OfType(Of TextBox)()
            AddHandler t.TextChanged, AddressOf ValidateInputs
        Next t
        'Also adding below handlers for comboxs to check for value change
        AddHandler cboStaff_id.TextChanged, AddressOf ValidateInputs
        AddHandler cboPub_id.TextChanged, AddressOf ValidateInputs
        AddHandler cboSub_Code.TextChanged, AddressOf ValidateInputs
        AddHandler DateTimePicker1.TextChanged, AddressOf ValidateInputs
    End Sub
Private Sub btnUpdate_Click(sender As Object, e As EventArgs) Handles btnUpdate.Click
 'creating a FOR EACH LOOP to check all comboboxes for value presence
        For Each cbo As ComboBox In GroupBox1.Controls.OfType(Of ComboBox)()
            AddHandler cbo.TextChanged, AddressOf ValidateInputs
        Next cbo
        'Also adding below handlers for textboxes to check for value change
        AddHandler txtbook_name.TextChanged, AddressOf ValidateInputs
        AddHandler txtauthor.TextChanged, AddressOf ValidateInputs
        AddHandler txtprice.TextChanged, AddressOf ValidateInputs
        AddHandler txtrack_no.TextChanged, AddressOf ValidateInputs
        AddHandler TxtNo_of_Books.TextChanged, AddressOf ValidateInputs
        AddHandler txtvol_no.TextChanged, AddressOf ValidateInputs
        AddHandler DateTimePicker1.TextChanged, AddressOf ValidateInputs
    End Sub
Private Sub ValidateInputs(ByVal Sender As Object, ByVal e As EventArgs)
    Dim ctrl As Control
    Dim strErrorList As String
    strErrorList = ""
    For Each ctrl In Me.Controls
        If Len(ErrorProvider1.GetError(ctrl)) > 0 Then
            strErrorList += ErrorProvider1.GetError(ctrl) & ChrW(10) &
            ChrW(13)
        End If
    Next
    If Len(strErrorList) = 0 Then
        ' Process stuff if no errors
        btnsave.Enabled = Not GroupBox1.Controls.OfType(Of TextBox).Any(Function(t) t.Text = String.Empty) And 
       Not (cboStaff_id.Text = String.Empty OrElse cboPub_id.Text = String.Empty OrElse cboSub_Code.Text = String.Empty _
            OrElse DateTimePicker1.Text = " ")
        btnSaveUpdate.Enabled = Not GroupBox1.Controls.OfType(Of ComboBox).Any(Function(cbo) cbo.Text = String.Empty) And _
            Not (txtbook_name.Text = String.Empty OrElse txtauthor.Text = String.Empty OrElse txtprice.Text = String.Empty _
                 OrElse txtrack_no.Text = String.Empty OrElse TxtNo_of_Books.Text = String.Empty OrElse txtvol_no.Text = String.Empty OrElse DateTimePicker1.Text = " ")
        btndelete.Enabled = Not (cboISBN.Text = String.Empty)
    Else
        btnsave.Enabled = False
        btnSaveUpdate.Enabled = False
        MessageBox.Show(strErrorList, "List Of Errors")
    End If
End Sub

Posted 10-Dec-15 20:48pm

Hazmat HN

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CHill60 11-Dec-15 3:44am

What do you mean by "somehow it is not working" - what is / is not happening?
Have you tried debugging it?

Hazmat HN 11-Dec-15 5:02am

Above code enables save/update button When I still have error in errorprovider this should not happen!!!

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CHill60 · Answer 1 · 2015-12-10T23:05:00

Assigning the handlers within the button methods doesn't look right to me - you could add them multiple times and if those buttons are disabled then you'll never validate the inputs.

Here I present a simple form with two textboxes and a button. The button is disabled at the outset and only enabled when both textboxes have something in them

VB.NET

Public Class Form1
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        AddHandler TextBox1.TextChanged, AddressOf AllComplete
        AddHandler TextBox2.TextChanged, AddressOf AllComplete
        btnInsert.Enabled = False
    End Sub
    Private Sub TextBox1_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
        If String.IsNullOrWhiteSpace(TextBox1.Text.Trim()) Then
            e.Cancel = True
        End If
    End Sub
    Private Sub TextBox2_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles TextBox2.Validating
        If String.IsNullOrWhiteSpace(TextBox2.Text.Trim()) Then
            e.Cancel = True
        End If
    End Sub
    Private Sub AllComplete(ByVal sender As Object, ByVal e As EventArgs)
        Dim validated As Boolean = Me.ValidateChildren()
        btnInsert.Enabled = validated
    End Sub
End Class

The key points here are:
- The checking for all of the controls being complete happens on the TextChanged event - thus the user must have at least attempted to enter some data before the button is enabled
- The ValidateChildren()[^] function will call all of the Validating events on the form (so don't call the AllComplete method from any Validating event!)
- If the user goes back to a control and deletes the contents after the button has been enabled it is disabled again.

I haven't used an ErrorProvider in this example because all that is doing is highlighting the control that is incorrect and adds nothing to the demonstration of the principle used here.

It is also worth noting that you can't close the form until data has been entered into all of the controls tested. You can get around that by adding the following code