An abstract class that serves as the base class for Collection Source classes.
To display a collection of objects in a UI, the eXpressApp Framework uses List Views. These Views allow end-users to browse and manipulate a collection of objects of the same class, whether persistent or not. By default, a List View is displayed as a grid in which a column represents the class’ property and a row represents a single object.
A Collection Source serves as the data source for a List View. A Collection Source is a mediator between a List View and an Object Space (see BaseObjectSpace). A Collection Source retrieves a typed collection of objects from an ObjectSpace, stores them in the internal CollectionSourceBase.Collection and feeds this collection to a List View. Besides object retrieval, a Collection Source exposes additional methods that allow a List View to manipulate the Collection Source’s object collection. These include methods to add and remove objects from the Collection Source’s collection, methods that deal with the collection filtering, various event notifications and more.
The CollectionSourceBase class is an abstract class from which all the Collection Sources derive. The following table lists XAF’s built-in Collection Sources.
|CollectionSource||Used by default for the root List Views.|
|PropertyCollectionSource||Used by the nested List Views that display collection properties.|
|LookupEditPropertyCollectionSource||Used by the Lookup Property Editors‘ List Views.|
XAF automatically creates and manipulates a Collection Source when it creates a List View. However, there are few typical tasks that require you to instantiate or access a Collection Source manually. Here they are:
- Create a custom List View. To be able to do it, you need to first create the required collection source.
- Filter a collection of objects that a List View displays on the data source level. To do so, you need to access the List View’s Collection Source. The Criteria Property of a List View’s Collection Source topic describes this.
There are certain rare cases in which you may need to create a custom Collection Source. While implementing a custom Collection Source derived from the CollectionSourceBase class, the following methods, not described in the documentation, can be overridden.
Abstract. Filters the Collection Source’s collection using the specified CriteriaOperator.
Returns a Boolean value that indicates whether an object can be added to the Collection Source’s collection. For instance, if the Collection Source’s collection has not been instantiated, this method returns false.
Returns a Boolean value that indicates whether an object can be removed from the Collection Source’s collection. For instance, if the Collection Source’s collection is read-only, this method returns false.
This method returns an estimate on the total number of objects in the Collection Source’s CollectionSourceBase.Collection. The value returned by this method is used to decide whether or not the search functionality must be enabled for a Lookup Property Editor’s List View. The returned value is considered if the IModelCommonMemberViewItem.LookupEditorMode property of the BOModel | <Class> | OwnMembers | <Member> node that corresponds to the property being edited, is set to Auto.
Called in the private EnsureCollection method, invoked by the CollectionSourceBase.ResetCollection method, after the Collection Source’s collection has been recreated. Raises the CollectionSourceBase.CollectionChanged event.
Called in the protected ApplyCriteria method before the ApplyCriteriaCore method has been called. Raises the CollectionSourceBase.CriteriaApplying event.
Called in the protected ApplyCriteria method after the ApplyCriteriaCore method has been called. Raises the CollectionSourceBase.CriteriaApplied event.
Called after the CollectionSourceBase.Criteria dictionary has been changed. Override this method in your descendant to throw an exception, if your Collection Source’s collection does not support changing the criteria applied to it.
Abstract. Creates and returns a collection of the CollectionSourceBase.ObjectTypeInfo.Type objects. The collection’s objects satisfy the criteria passed as the method’s first parameter. The collection’s objects are sorted in the order specified by the method’s second parameter.