Question

I took many hours trying to solve this problem I have attempted, without success.
All I need is to validate a textbox:

Valid Chains:

10% 
 0% 
 1111111.12% 
 15.2% 
 10 
 2.3 

Invalid Chains:

 .% 
 12.% 
 .02% 
 % 
 123456789123.123 

I need to validate the textbox with these valid chains, supporting the keypress event.

I tryed:

Private Sub prices_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles wholeprice_input_new_item.KeyPress, dozenprice_input_new_item.KeyPress, _
            detailprice_input_new_item.KeyPress, costprice_input_new_item.KeyPress

            Dim TxtB As TextBox = CType(sender, TextBox)
            Dim fullText As String = TxtB.Text & e.KeyChar
            Dim rex As Regex = New Regex("^[0-9]{1,9}([\.][0-9]{1,2})?[\%]?$ ")

            If (Char.IsDigit(e.KeyChar) Or e.KeyChar.ToString() = "." Or e.KeyChar = CChar(ChrW(Keys.Back))) Then
                If (fullText.Trim() <> "") Then
                    If (rex.IsMatch(fullText) = False And e.KeyChar <> CChar(ChrW(Keys.Back))) Then
                        e.Handled = True
                        MessageBox.Show("You are Not Allowed To Enter More then 2 Decimal!!")
                    End If
                End If
            Else
                e.Handled = True
            End If
        End Sub

NOTE: The regex has to validate (Maximum 2 decimal places, and 9 integers) with an optional percent symbol.

Please help, I feel so frustrated trying to solve the problem without success

Answer 1

I think that you almost had the right answer. When I run your regex against the samples you supplied, they all fail. But if I remove the extra space at the end of the regex I get the expected successes and failures.

So currently your regex looks like this:

Dim rex As Regex = New Regex("^[0-9]{1,9}([\.][0-9]{1,2})?[\%]?$ ")

and it should look like

Dim rex As Regex = New Regex("^[0-9]{1,9}([\.][0-9]{1,2})?[\%]?$")

EDIT:

Ok I understand the issue more. The problem with the regex is that it will only allow a period if it is followed by one or two numbers. That works fine if you are evaluating the textbox value after someone has finished typing. But in your code, you are evaluating for each keypress, so you don’t have a chance to type a number after the “.”

I can see two possible solutions

1. Change the regex to allow 1. as a valid entry
2. Change when you evaluate the regex, perhaps trying to figure out a way to only evaluate the regex when the person has paused typing.

If you went with option 1, then we need to tweak the regex to something like this

"^[0-9]{1,9}((\.)|(\.[0-9]{1,2}(%)?)|(%))?$"

I changed the regex so that it will accept three optional endings to the text string (\.) will allow the string to end in a period , (\.[0-9]{1,2}(%)?) will allow the string to end period followed by one or two numbers and an optional percent sign, and (%) will allow the string to end in a percent sign. I broke the ending into the three options because I didn’t want to allow something like 12.% to be valid. Also for this to work you will also need to add the percent sign to your first If statement

If (Char.IsDigit(e.KeyChar) Or e.KeyChar.ToString() = "." Or e.KeyChar.ToString() = "%" Or e.KeyChar = CChar(ChrW(Keys.Back))) Then

so that the regex runs when someone types the percent sign.