Automatically handle null values in DateTimePIcker - vb.net

Question

I've read various workarounds on this, but cannot get any working well. I have a large number of Datetimepickers on a form, all bound to datatables via a BindingSource. Problem being, a lot of the data holds null values for dates, but these display as datetime.now. I want some indication that these are null, not an actual date.
As it happens, I have a 'themer' that iterates through all controls on the form. I add a handler to each on ValueChanged:
ElseIf TypeOf ct Is DateTimePicker Then
Dim dtp = DirectCast(ct, DateTimePicker)
With dtp
AddHandler dtp.ValueChanged, AddressOf Zzapper.Dtp_ValueChanged
End With
Handler:
Public Sub Dtp_ValueChanged(ByVal sender As Object, ByVal e As EventArgs)
Dim dtp As DateTimePicker = DirectCast(sender, DateTimePicker)
Dim result As DateTime
If DateTime.TryParse(dtp.Value, result) Then
dtp.Format = DateTimePickerFormat.Long
Else
dtp.CustomFormat = " "
dtp.Format = DateTimePickerFormat.Custom
End If
However, this does not get fired on null values (discerned via breakpoints and counting how often it gets called - only gets called for non-null values), I'm guessing because technically the value doesn't change in the control itself.
Can anyone else think of a solution?

Answer 1

I created a DataTable. I presume yours came from a database. In the DefaultForNull method I just looped through the columns I needed to check and inserted a default value for the missing dates.
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim dt As New DataTable
dt.Columns.Add("Date1", GetType(Date))
dt.Columns.Add("Date2", GetType(Date))
dt.Columns.Add("Date3", GetType(Date))
dt.Rows.Add({#3/19/2021#, DBNull.Value, #3/20/2020#})
dt.Rows.Add({DBNull.Value, #7/12/2020#, #8/4/2021#})
DefaultForNullDates(dt, #1/1/1900#)
For Each row As DataRow In dt.Rows
Debug.Print($"{row(0).ToString}, {row(1).ToString}, {row(2).ToString}")
Next
End Sub
Private Sub DefaultForNullDates(dt As DataTable, DefaultDate As Date)
Dim lst As New List(Of String) From {"Date1", "Date2", "Date3"}
For Each ColName In lst
For Each row As DataRow In dt.Rows
If row(ColName) Is DBNull.Value Then
row(ColName) = DefaultDate
End If
Next
Next
End Sub
Depending on your database you can probably do this directly in you select query.