Pickers provide a consistent user experience for selecting objects. Typically, you declare a Picker (.picker file) for a class or enumeration. This configures the captions, icons, searching, filtering, and paging of the picker dialog that displays when users need to select instances of the class or options within the enumeration. Multipicker and single picker controls can then reuse the Picker definition in portlet layouts.

A multipicker control allows you to pick many items.

The following example is a simplified version of the multipicker used to select contacts for a schedule item, and defined in ScheduleItemDetailEdit.layout.

<Multipicker
	caption="IDS_FOR"
    captions="entityFullName"
    icons="(image . (entity image))(data . mimeData)(type . mimeType)(icon . (entity icon))(default . "contact")"
    items="(@ userParticipants)"
    mode="ScheduleItem entityParticipants"
    name="pickParticipantsLink"
    order="(((@ entity lastName) . #t) ((@ entity firstName) . #t) ((@ entity) . #t))"
    ref="mda:Entity"/>
/>  

The multipicker control supports type-ahead, and has a Select  button to open its picker dialog based on a reference to a picker (.picker file) declaration. It is bound to a collection attribute that points to an intersection class in a many-to-many relationship. It picks from a class through an intersection to create records in the intermediate intersection table.

The following illustrates the structure of a many-to-many association:

A - Class to which the containing Layout is bound.

B - Class you are picking.

AB - Intersection class between A and B.

a b - Association path between A and B through the intersection class AB.

a - Collection attribute on class A of type AB. The picker's collection is bound to this attribute.

For example:

The important properties are:

• Caption - displays on the picker dialog. This is the only property from the control that directly affects the dialog's display.
• Captions - the association path or expression to the captions for the selected items, usually displayed as chips. The path to the attribute to display is from the perspective of the intersection class. For example, UserParticipations'entityFullName > entityFullName.
• Icons - the association path or expression to the icons for the selected items, usually displayed as images in chips. The path to the attribute to display is from the perspective of the intersection class. For example, (UserParticipation'entity) image)  > (entity image).
• Items - the association path to the intersection class. For example, (@ userParticipants).
• Mode - when used with a multipicker, the mode declares the association from the picker class back to the class to which the multipicker's containing layout is bound, as well as the factory for creating new intersection instances. For example, when picking UserPerson instances to associate with a Task through the UserParticipation intersection class, we specify the mode's association to userParticipations and the selection to Task userParticipants.
• Order - the orderby statement for the selected items. The path to the attributes to sort by is from the perspective of the intersection class. For example, (UserParticipation'entity) lastName) → ((@ entity lastName) . #t).
• Ref - a reference to the .picker declaration. The type of the .picker must work with the type of the value property.

If you type in the list, based on the configuration above, you get:

and the selected items will look like:

Clicking the picker control's Select button displays the picker dialog as declared in the .picker file with the caption set by the picker control.

The drop-down list enables you to select additional items when required, and the pop-up picker dialog displays checkboxes rather than radio buttons (multiple selection versus single selection).

To learn more about the various properties of a multipicker control, see MultiPicker Control in the Model Description Language Reference.

Related APIs

Picker (.picker file) declaration for multi-item pickers

The picker declaration for multi-item picking is dependent on the modes. The approach for captions, icons, order, and search is the same as with single-item pickers.

The following example is for the UserPerson class.

<Picker 
   captions="fullNameFirstLast" 
   class="UserPerson" 
   icons="(image . image)(data . mimeData)(type . mimeType)(icon . icon)(default . "icon:person")" 
   order="(((@ firstName) . #t) ((@ lastName) . #t) ((@) . #t))" 
   search="fullTextSearch"">
/>

The mode declares the association from the picker class back to the class and attribute for which the items are being picked. There may be many modes configured for multipicking; possibly as many modes as there are outgoing many-to-many associations from the picker class.

The properties for a mode used for multi picking are:

• Association - the association path from the item being picked to the intersection class. For example, userParticipations.
• Factory - the new item factory event for new intersection instances, <class> <event> or <event> if the event is on the picker class. The typical configuration is <class> <event>. For example, UserParticipation create.
• Name - the picker mode name. It should be something meaningful from the other side of the association. It defaults to the selection, which should usually make sense. For example, Task userParticipants.
• Selection - the class name and association attribute name from the other side of this many-to-many association. For example, Task userParticipants.

The following example is for the Task userParticipants mode of the UserPerson class picker.

<Mode
   assoc="userParticipations"
   factory="UserParticipation create"
   name="Task userParticipants"
   selection="Task userParticipants"/>
/>

Learn more about the various properties of a .picker declaration in the Model Description Language Reference.

Other considerations

Advanced picker (.picker file) declaration

Picker declarations may also specify that they have a filter. The chips that appear for the filter may be limited by using the subject property.

In addition, you can override the generated picker table by specifying your own table columns and headings.

Using pickers in filters

In addition to being used in picker and multipicker controls, pickers may be referenced in Filter Fields to provide picker capabilities for filtering lists.

Using pickers in Script 

Pickers may also be used in Script. The openPickerDialog method on the controller API allows you to call a pre-defined picker from Script.

The following code enables a user to pick a number of participants in a conversation and then continuing processing based on the selection.

(define conversation (@ model item : (parameter'index)))
(define participants
   (@ openPickerDialog :
      "mda:ConversationParticipantPicker"
      (: where `(not (in? (@) ,(map (lambda (p) (p'entity)) (conversation'activeParticipants)))))
      (: factory '(ConversationParticipant createConversationParticipant))
      (: values "entity")
      (: parameter (list (: conversation conversation)))
   )
)
(unless (null? participants)
  ...

openPickerDialog also supports generic pickers. This creates a default picker for a class without the use of a pre-defined .picker file. The method supports both single and multi-picker modes. This is an experimental feature.

Custom pickers

Custom pickers are used infrequently. If the picking requirements are very specialized, there are ways to build a custom control in Application Foundation Layers (AFL). This information is not covered here, but an example can be seen in the finance-ai service.

Related links

• Working with pickers (in the Learning Center)
• MultiPicker Control and Picker file information (in the Model Description Language Reference)