Why is this CInt function call *not* throwing an error? - vb.net

Question

I'm just curious, really.
There was some code that wasn't handling empty strings before converting, essentially calling
Dim StringToConvert As String = ""
Dim a As Integer = CInt(StringToConvert)
Rather then something like
Dim StringToConvert As String = ""
Dim a As Integer = CInt("0" & StringToConvert)
and so it makes sense that it would throw an error...
What I don't understand is that this wasn't throwing an error on my machine when I was debugging. But it does throw an error when compiled!
Here is what calls the CInt function and only sometimes throws an error:
Public NotInheritable Class SomeForm
Inherits Windows.Forms.Form
Private Sub TextBox_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) _
Handles TextBox.LostFocus
StaticHolderClass.StaticMethod(DirectCast(sender,TextBoxBase))
End Sub
End Class
Public NotInheritable Class StaticHolderClass
Public Shared Sub StaticMethod(ByVal sender As Windows.Forms.TextBoxBase)
sender.Text = Format(CInt(sender.Text),"#,#")
End Sub
End Class
Does anyone know why this would happen?

Answer 1

In VB, occasionally when an error is encountered during form initialization, it doesn't get reported properly. Sometimes the error is not flagged at all, and sometimes it appears to be from a different location. For example, in the following code (on my system), an error is thrown with the button click and not the form load:
Public Class Form1
Dim k As Integer
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
k = CInt("")
End Sub
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
k = CInt("")
End Sub
End Class
It seems to depend on the environment, so "your results may vary". You can work around this sometimes by using the shown event rather than load.