One of the popular ways to do this - change format to " " (space) whenever null value is being set and roll it back to the old format on anything else. I have been looking for clean implementation of this approach. In the end I decided to write my own, using source code available on the net. Here is what I came up with:
Public Class MyDateTimePicker : Inherits DateTimePicker
Private oldFormat As DateTimePickerFormat
Private oldCustomFormat As String
Private _value As Object
Public Sub New()
_value = MyBase.Value
End Sub
Public Overloads Property Value()
Get
Return _value
End Get
Set(ByVal value)
If value = DateTime.MinValue Then
If _value IsNot Nothing Then
oldFormat = Me.Format
oldCustomFormat = Me.CustomFormat
End If
Me.Format = DateTimePickerFormat.Custom
Me.CustomFormat = " "
_value = Nothing
Else
If _value Is Nothing Then
Me.Format = oldFormat
Me.CustomFormat = oldCustomFormat
End If
MyBase.Value = value
_value = value
End If
End Set
End Property
Private Sub MyDateTimePicker_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown
Select Case e.KeyCode
Case Keys.Delete
Me.Value = DateTime.MinValue
End Select
End Sub
Protected Overrides Sub OnValueChanged(ByVal eventargs As System.EventArgs)
If _value Is Nothing Then
Me.Format = oldFormat
Me.CustomFormat = oldCustomFormat
End If
_value = MyBase.Value
End Sub
End Class
In the code above, Delete key sets value to null. And it keeps Nothing until reassigned to something else. You can download test project from here.
