Single Selection in ProtoListPicker-based Views

One of the Newton 2.x OS Q&As
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This document was exported on 7/23/97.

Single Selection in ProtoListPicker-based Views (9/20/96)

Q: How do I allow only one item to be selected in a protoListPicker, protoPeoplePicker, protoPeoplePopup, or protoAddressPicker?

A: The key to getting single selection is that single selection is part of the picker definition and not an option of protoListPicker. That means that the particular class of nameRef you use must include single selection. In general, this requires creating your own subclass of the particular name reference class.

The basic solution is to create a data definition that is a subclass of the particular class that your protoListPicker variant will view. That data definition will include the singleSelect slot. As an example, suppose you want to use a protoPeoplePopup that just picks individual people. You could use the following code to bring up a protoPeoplePopup that only allowed selecting one individual at one time:

    // register the modified data definition    RegDataDef('|nameref.people.single:SIG|,    {_proto: GetDataDefs('|nameRef.people|), singleSelect: true});    // then pop the thing    protoPeoplePopup:New('|nameref.people.single:SIG|,[],self,[]);    // sometime later    UnRegDataDef('|nameref.people.single:SIG|);

 For other types of protoListPickers and classes, create the appropriate subclass. For example, a transport that uses protoAddressPicker for emails might create a subclass of '|nameRef.email| and put that subclass symbol in the class slot of the protoAddressPicker.

Since many people are likely to do this, you may cut down on code in your installScript and removeScript by registering your dataDef only for the duration of the picker. That would mean registering the class just before you pop the picker and unregistering after the picker has closed. You can use the pickActionScript and pickCanceledScript methods to be notified when to unregister the dataDef.