I am creating a .net project and am adding custom renderers. I have this code for creating the date field into 3 listboxes, the Month, theDay and theYear. I would like to add an on_change() event (or some such mechanism) to change theDay from 1-31 to the appropriate number of days (I have to consider leap years too).

---------------- Beginning of code -------------------------
Imports System.ComponentModel
Imports System.Web.UI

<ToolboxData("<{0}:DateRenderer runat=server></{0}:DateRenderer>")> Class DateRenderer
    Inherits AbstractFieldRenderer

    Private Shared ReadOnly DEFAULT_DATE = Now()

    Private Shared log As log4net.ILog = log4net.LogManager.GetLogger("DateRenderer")

    Public Overloads Sub onInit(ByVal sender As Object, ByVal e As EventArgs) Handles MyBase.Init

        Dim theMonth As New ListBox
        '' theMonth.Width = Unit.Parse("21pt")
        theMonth.ID = Me.ID & "_theMonth"
        theMonth.Items.Add(New ListItem("Jan", "01"))
        theMonth.Items.Add(New ListItem("Feb", "02"))
        theMonth.Items.Add(New ListItem("Mar", "03"))
        theMonth.Items.Add(New ListItem("Apr", "04"))
        theMonth.Items.Add(New ListItem("May", "05"))
        theMonth.Items.Add(New ListItem("Jun", "06"))
        theMonth.Items.Add(New ListItem("Jul", "07"))
        theMonth.Items.Add(New ListItem("Aug", "08"))
        theMonth.Items.Add(New ListItem("Sep", "09"))
        theMonth.Items.Add(New ListItem("Oct", "10"))
        theMonth.Items.Add(New ListItem("Nov", "11"))
        theMonth.Items.Add(New ListItem("Dec", "12"))
        Me.Parent.Controls.Add(theMonth)


        Dim theDay As New ListBox
        'theDay.Width = Unit.Parse("14pt")
        theDay.ID = Me.ID & "_theDay"
        Dim i As Integer
        For i = 1 To 31
            theDay.Items.Add(New ListItem(i, i))
        Next

        Dim theYear As New ListBox
        'theYear.Width = Unit.Parse("28pt")
        theYear.MaxLength = 4
        theYear.ID = Me.ID & "_lastFour"
        Dim x As Integer = System.DateTime.Today.Year
        For i = 1900 To x
            theYear.Items.Add(New ListItem(i, i))
        Next

        Dim theMonthRequiredValidator As New RequiredFieldValidator
        theMonthRequiredValidator.ControlToValidate = Me.ID & "_theMonth"
        theMonthRequiredValidator.ErrorMessage = "Choose a month, this field is required."
        theMonthRequiredValidator.Display = ValidatorDisplay.None

        Dim theDayRequiredValidator As New RequiredFieldValidator
        theDayRequiredValidator.ControlToValidate = Me.ID & "_theDay"
        theDayRequiredValidator.ErrorMessage = "Choose a day, this field is required."
        theDayRequiredValidator.Display = ValidatorDisplay.None

        Dim theYearRequiredValidator As New RequiredFieldValidator
        theYearRequiredValidator.ControlToValidate = Me.ID & "_theYear"
        theYearRequiredValidator.ErrorMessage = "Choose a year, this field is required."
        theYearRequiredValidator.Display = ValidatorDisplay.None

        Me.Parent.Controls.Add(theMonthRequiredValidator)
        Me.Parent.Controls.Add(theDayRequiredValidator)
        Me.Parent.Controls.Add(theYearRequiredValidator)

        Me.Parent.Controls.Add(theMonth)
        Me.Parent.Controls.Add(theDay)
        Me.Parent.Controls.Add(theYear)

    End Sub
End Class
---------------- End of code -------------------------
Thanks for the help!