I achieve this by handling the Binding Source that the control is binding to and enabling the ShowCheckBox property.

The .NET DateTimePicker doesn’t accept blank or NULL value. I’ve seen many posts online that extend the controller to accept NULL value like this one or some other posts to change the formatting to custom and switching back again.

So if you don’t feel like adding a new custom control to your project just handle the underlying data source.

Since I had many of the DateTimePicker controls, I made one function that handles the Leave event of each one like so:

    Private Sub DateTimePicker_Leave(sender As System.Object, e As System.EventArgs) Handles Inv_OriginalDateTimePicker.Leave
        'Handle the DateTimePicker so when it is unchecked it saves Null value
        Dim dt As DateTimePicker = sender

        If Not dt.Checked Then
            'Get the current record
            Dim row = DirectCast(Me.PO_JobsBindingSource.Current, DataRowView)

            row(dt.DataBindings.Item("Value").BindingMemberInfo.BindingField.ToString) = DBNull.Value

        End If
    End Sub

The other day I wanted to add news tags feature to a program, and to make it easy I wanted the user to be able of adding and removing news tags by double clicking a Listbox of available tags and assigned tags.

If you need to move items between bound Listboxes you cannot just use the Listbox.Add or Listbox.Remove methods. Instead you should add and remove rows to the Tables which they’re bound to.

This is the code I used:

    Private Sub AvailableTagListBox_DoubleClick(sender As System.Object, e As System.EventArgs) Handles AvailableTagListBox.DoubleClick
        If Not IsNothing(AvailableTagListBox.SelectedItem) Then
            'We are making a new row to be added to the table which then will appear in the listbox
            Dim Customer_News_Tags_Row As DataRow = MyDataSet.Customer_News_Tags.NewRow
            'Since I have a Parent and Child relation I'm taking the current parent ID
            Dim NewsRow = DirectCast(Me.Customer_NewsBindingSource.Current, DataRowView)
            'Parent ID
            Customer_News_Tags_Row("News_ID") = NewsRow("ID")
            'Fill the listbox item display field which I have it bound to
            Customer_News_Tags_Row("Tag") = AvailableTagListBox.Text

            'Adding new item to the other listbox by adding new row to its table
            MyDataSet.Customer_News_Tags.AddCustomer_News_TagsRow(Customer_News_Tags_Row)
            'Delete the listbox item by deleting the row in its table
            MyDataSet.News_Tags.Select("ID=" & AvailableTagListBox.SelectedValue)(0).Delete()

        End If

    End Sub

    Private Sub AssignedTagListBox_DoubleClick(sender As System.Object, e As System.EventArgs) Handles AssignedTagListBox.DoubleClick
        If Not IsNothing(AssignedTagListBox.SelectedItem) Then

            Dim News_Tags_Row As DataRow = MyDataSet.News_Tags.NewRow
            'I'm using a field called Tag
            News_Tags_Row("Tag") = AssignedTagListBox.Text

            MyDataSet.News_Tags.AddNews_TagsRow(News_Tags_Row)
            'Here I'm matching with a field I have called Tag to delete from Assigned listbox items
            MyDataSet.Customer_News_Tags.Select("Tag='" & AssignedTagListBox.SelectedValue & "'")(0).Delete()

        End If
    End Sub

Hope this helps, and if you need any clarifications let me know 🙂