Date Validation - Only enter dates within current month

Question

I've been assigned the task of validating a date field that gets populated when creating an invoice. It is a text box with three button objects that allow a user to select a date from a calendar, enter today's date, or remove the date entry.

My task is to make sure that users cannot enter a date that is NOT within the current month (double negative...tricky). My task is to make sure that users can only enter dates within the current month. (better?)

I have no idea how to do this. Should I use the asp controls or do this on the back end?

I'm using VB.NET.

Answer 1

Use the ASP.NET Validator controls, like this:

Markup:

<asp:TextBox id="YourTextBox" runat="server" />

<asp:RequiredFieldValidator ControlToValidate="YourTextBox" 
    Text="The date field is required!" runat="server" />
<asp:CompareValidator ID="compareValidatorDate" ControlToValidate="YourTextBox" 
    Type="Date" Operator="LessThan" ErrorMessage="Date must be from this month!"
    Display="Dynamic" runat="server" />

Note: I have included the RequireFieldValidator to ensure that we have a value to compare against for the date validation.

Code-behind ( Page_Load ):

If Not IsPostBack Then
    Dim firstOfTheMonthDate As DateTime = FirstDayOfMonthFromDateTime(DateTime.Now)
    Me.compareValidatorDate.ValueToCompare = firstOfTheMonthDate.ToString("d")
End If

Code-behind (utility function):

Public Function FirstDayOfMonthFromDateTime(dateTime As DateTime) As DateTime
    Return New DateTime(dateTime.Year, dateTime.Month, 1)
End Function

Note: I included a function to determine the date for the first day of the current month. The Page_Load is calling that function and then passing that to the validator as the value to compare for less than.