ASP.Net：RegularExpressionValidator ValidationExpression一次防止`;`和`-`

Question

I want to make an ASP.Net RegularExpressionValidator ValidationExpression that will prevent to give input ; and –- .

I can do it for – and it is ValidationExpression="[^-]*" .

<asp:RegularExpressionValidator ID="RegularExpressionValidator1"
      runat="server" 
      ControlToValidate="TextBox1" Display="Dynamic" ErrorMessage="**" 
      ValidationExpression="[^-]*"></asp:RegularExpressionValidator>

Above expression can prevent single – character. I will give permission for single – character. I will block for double – characters ( -- ). I need to prevent ; and – at a time.

Can anyone help me?

Answer 1

The Regex needs to get smarter. You want to block multiple hyphens, the m-dash, and semicolons.

So, try @"^(?=[^–;]*)((?!--).)*$"

Breaking it down:

The ^ matches the start of a line, and helps ensure that the validator is used to match the entire string.

The expression in the first set of parentheses will match any set of characters that do not include the m-dash and semicolon. You may want to substitute the hex value for the m-dash using the \\x2014 escape sequence. It is defined as non-consuming with the ?= , meaning the Regex engine must match this pattern but will not advance its index when it finds the match, so the same set of characters will be tested for the next pattern as well.

The expression in the second set of parentheses is an inverse look-ahead; it will match any set of characters not containing two (or more) adjacent hyphens. This may be a bit slow, however; this regex basically forces the Regex engine to consider each character one at a time, looking ahead from that point to ensure the next character won't make match the inverse pattern.

The trailing $ marks the end of a line; together with the ^ it ensures that you are looking at everything in a single string (or line in multiline data) when determining a match.

Plug this into a Regex tester like Derek Slater's and play around with it to make sure it will stop all the scenarios you want.