No, this is for ComboBox. Native DTP control is quite a nod. It supports the DTM_CLOSEMONTHCAL message to close the calendar, but does not have a corresponding message to open it. You will need to do something ugly, like a mock mouse or keyboard input. The latter is probably best:
Private Sub ShowMonthCalendar_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ShowMonthCalendar.Click
DateTimePicker1.Focus()
SendKeys.Send("{F4}")
End Sub
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