Change invalid textbox value - VB NET - vb.net

Question

I currently have 3 textboxes. Each textbox must contain a number. If any one of the three textboxes does not contain a numeric value, show an error message. For textboxes not displaying a number, (where IsNumeric returns false), I want to change its default value. How do I do this?
If Not (IsNumeric(txtpadult.Text)) Or Not (IsNumeric(txtpjunior.Text)) Or Not (IsNumeric(txtpconc.Text)) Then
MsgBox("ERROR: INVALID NUMERIC !", vbCritical, "System Message")
End if
Thanks in advance.

Answer 1

First, I would recommend using the new .NET methods, when possible, rather than resorting to the old VB6 style methods. So, instead of MsgBox, I would recommend using MessageBox.Show, and instead of IsNumeric, I would use Integer.TryParse, etc.
So, for instance, you could rework your code like this:
Dim invalid As TextBox = Nothing
If Not Integer.TryParse(txtpadult.Text, 0) Then
invalid = txtpadult
ElseIf Not Integer.TryParse(txtpjunior.Text, 0) Then
invalid = txtpjunior
ElseIf Not Integer.TryParse(txtpconc.Text, 0) Then
invalid = txtpconc
End If
If invalid IsNot Nothing Then
MessageBox.Show("ERROR: INVALID NUMERIC !", "System Message", MessageBoxButtons.OK, MessageBoxIcon.Error)
invalid.Text = "0" ' Set to default value
End If
As you can see, as it tests each text box, if it finds one that is invalid, it keeps a reference to it in the invalid variable. Then it can check to see if one was found and set it's value. Alternatively, you could create a list of text boxes which need to be checked and then loop through them, like this:
Dim textBoxes() As TextBox = {txtpadult, txtpadult, txtpconc}
Dim invalid As TextBox = Nothing
For Each i As TextBox In textBoxes
If Not Integer.TryParse(i.Text, 0) Then
invalid = i
Exit For
End If
Next
If invalid IsNot Nothing Then
MessageBox.Show("ERROR: INVALID NUMERIC !", "System Message", MessageBoxButtons.OK, MessageBoxIcon.Error)
invalid.Text = "0" ' Set to default value
End If
Or, if you want to be clever, you can do it in less lines of code with a LINQ extension method:
Dim textBoxes() As TextBox = {txtpadult, txtpadult, txtpconc}
Dim invalid As TextBox = textBoxes.FirstOrDefault(Function(x) Not Integer.TryParse(x.Text, 0))
If invalid IsNot Nothing Then
MessageBox.Show("ERROR: INVALID NUMERIC !", "System Message", MessageBoxButtons.OK, MessageBoxIcon.Error)
invalid.Text = "0" ' Set to default value
End If