Drop combo box

A combo box usually requires two data sources. One is a single field or referenced instance displayed in the single line edit control on top of the combo box. The other is a collection to be displayed when the list is expanded.

The control data source will be displayed in the single line edit/display field of the box. The data source for the list can be defined in the Base Collection definition of the data source. When no base collection is defined, the default base collection defined in the object model will be displayed in the list.

In order to use combo boxes for selecting a single instance in a collection, one may also define a collection as data source for the combo box control. No base collection must be defined for the data source in this case and the data source must be marked as collection ( collection must be switched on). In this case. the line control of the combo box displays the currently selected instance.

A drop combo box contains a single line edit field on top of the drop list that shows the current value of the data source. For relationships, the drop lists displays the instances from the relationships base collection. In order to change the referenced instance, one may pick up an item from the list and the new link will be created. In order to assign a new instance to a reference or relationship, one may enter the key for the new instance in the single line edit.

Usually, the combo box list displays the current order key or the identifying key of the collection. You