Question

I have recently made some changes to one of the subs within a form of my vb project and I am now getting an error whilst attempting to load the form. I have little idea what start index or Parameter name are with relation to a form, so don’t where to start looking to solve this issue. Here is the error message I get:

An error occurred creating the form. See Exception.InnerException for details.  The error is: StartIndex cannot be less than zero.
Parameter name: startIndex

The Sub that I have made changes to is the last sub in the code below called TextBox1changed_textchanged. I have added all but the last 5 lines as to limit the characters that can be put into the text box. This new code is edited from another forum page so I assume it should work correctly, but I can’t be sure as the form will no longer run.

Public Class frmAddQuantity

Private Sub frmFieldMaster_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    cmbStateRateSumRatio.Items.Clear()
    cmbStateRateSumRatio.Items.Insert(0, "State")
    cmbStateRateSumRatio.Items.Insert(1, "Rate")
    cmbStateRateSumRatio.Items.Insert(2, "Sum")
    cmbStateRateSumRatio.Items.Insert(3, "Ratio")


End Sub

Private Sub bttAddQUAtoDatabase_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bttAddQUAtoDatabase.Click

    AddQuantity("'" & TextBox1.Text & "', '" & TextBox2.Text & "', '" & cmbStateRateSumRatio.Text & "'")

    InitialiseAll()
    frmFieldMaster.InitialiseNewParameter()
    Me.Close()

End Sub

Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox2.TextChanged

    If TextBox2.Text <> "Enter SI Units" Then
        If cmbStateRateSumRatio.SelectedIndex <> -1 Then
            bttAddQUAtoDatabase.Enabled = True
        End If
    End If
End Sub

Private Sub cmbStateRateSumRatio_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbStateRateSumRatio.SelectedIndexChanged

    If TextBox1.Text <> "Enter Quantity" Then
        If TextBox2.Text <> "Enter SI Units" Then
            bttAddQUAtoDatabase.Enabled = True
        End If
    End If

End Sub

Private Sub TextBox2_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox2.TextChanged


    Dim charactersAllowed As String = " abcdefghijklmnopqrstuvwxyz1234567890^-*()."
    Dim Text As String = TextBox2.Text
    Dim Letter As String
    Dim SelectionIndex As Integer = TextBox2.SelectionStart
    Dim Change As Integer




    Letter = TextBox2.Text.Substring(SelectionIndex - 1, 1)
    If Letter = "/" Then
        Text = Text.Replace(Letter, "^(-")
        SelectionIndex = SelectionIndex - 1
    End If



    Letter = TextBox2.Text.Substring(SelectionIndex - 1, 1)
    If charactersAllowed.Contains(Letter) = False Then
        Text = Text.Replace(Letter, String.Empty)
        Change = 1
    End If


    TextBox2.Text = Text
    TextBox2.Select(SelectionIndex - Change, 0)

    If TextBox1.Text <> "Enter Quantity" Then
        If cmbStateRateSumRatio.SelectedIndex <> -1 Then
            bttAddQUAtoDatabase.Enabled = True
        End If
    End If

End Sub

End Class

Answer 1

Private Const AllowedChars = " abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890^-*()."

Private Sub TxtSIUnit_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtSIUnit.KeyPress
    If e.KeyChar >= " "c AndAlso Not AllowedChars.Contains(e.KeyChar) Then e.Handled = True
End Sub

Private Sub TxtSIUnit_KeyPress2(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtSIUnit.KeyPress
    Dim selectstart
    If e.KeyChar = "/" Then
        e.Handled = True
        selectstart = txtSIUnit.SelectionStart
        txtSIUnit.SelectedText = "*^-1"
        txtSIUnit.Select(selectstart + 1, 0)
    End If
End Sub

I have solved the issue above using this code. Instead of using the .textchanged handle I have used .keypress which stopped the issue I was having previously. The text in the textbox was changing as the form was loading, leading to a problem with the start index of the text. Using .keypress mean only user inputs let the code run, avoiding errors on loading.