ASP.NET client-side validation against a dynamically loaded list

If you need to validate some user input against a set of allowed values, you can use the RegularExpressionValidator by setting its ValidationExpression as follows:

EUR|USD|AUD|CHF

The '|' symbol delimits the set of allowed values in a regular expression.

If you need to load the list of allowed values from a database, config file or other source, you can do so, and simply set the ValidationExpression property of the RegularExpressionValidator at runtime.

Dim currencyDAL As New CurrencyDAL()
Dim currencies As List(Of String) = currencyDAL.SelectAll()
Dim expression As String = String.Join("|", currencies.ToArray)
currencyValidator.ValidationExpression = expression

Simple.