First, I will start with the TKDataFormPickerViewEditor - it uses the iOS UIPickerView as its editor. The UIPickerVIew control does not provide the option to have no selection - always one of the items should be selected. The selection propagates to the DataForm property.
I have attached a sample that shows how you can partially achieve the behavior by creating a custom renderer of the iOS platform. In short, you can change the initial value of the editor label, still, as soon as the picker is shown, the property value will be updated. Please have a look at the implementation and consider whether this approach would work for you.
As to the Date/Time pickers - we have a feature request regarding support for null value, you can cast your vote and track its status at the link below:
DataForm: [iOS] Consider improvements for null value support for date/time values
I am looking forward to your reply.
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