允许用户在文本框 VB.NET 2010 中只写一个点和数字

Question

I have a textbox and I am using the following to validate the user can only add numbers, but how can I let the user to write only one "."

Private Sub txtDiagnostic_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles txtConsultor.KeyPress
        If e.KeyChar <> ChrW(Keys.Back) Then
            If Char.IsNumber(e.KeyChar) Then
            Else
                e.Handled = True
            End If
        End If
    End Sub

I was planing to use contains() or something but how can I realize the textbox has only one dot ? or how to allow the user can write a single dot and only one?

Answer 1

add this line before your first IF

If (e.KeyChar.ToString = ".") And (txtDiagnostic.Text.Contains(e.KeyChar.ToString)) Then
     e.Handled = True
     Exit Sub
End If

Answer 2

try this code good for money purposes

    Private Sub LoanFeeTextBox_KeyPress(sender As Object, e As KeyPressEventArgs) Handles LoanFeeTextBox.KeyPress
        If Char.IsControl(e.KeyChar) Then
        ElseIf Char.IsDigit(e.KeyChar) OrElse e.KeyChar = "."c Then
            If LoanFeeTextBox.TextLength = 12 And LoanFeeTextBox.Text.Contains(".") = False Then
                LoanFeeTextBox.AppendText(".")
            ElseIf e.KeyChar = "." And LoanFeeTextBox.Text.IndexOf(".") <> -1 Then
                e.Handled = True
            ElseIf Char.IsDigit(e.KeyChar) Then
                If LoanFeeTextBox.Text.IndexOf(".") <> -1 Then
                    If LoanFeeTextBox.Text.Length >= LoanFeeTextBox.Text.IndexOf(".") + 3 Then
                        e.Handled = True
                    End If
                End If
            End If

        Else
            e.Handled = True
        End If
    End Sub