The container control can accommodate large amounts of data with an application-defined delta. The delta is an application-defined threshold, or number of container items, from either end of the list. The application is responsible for specifying the delta value in the CNRINFO data structure's cDelta field. It also is responsible for setting the delta value with the CMA_DELTA attribute of the CM_SETCNRINFO message's ulCnrInfoFl parameter.
The container control monitors its place in the list of container items when the user is scrolling through it. When the user scrolls to the delta from either end of the list, the container control sends a CN_QUERYDELTA notification code to the application as a request for more container items in the list.
The application is responsible for managing the records in the container. When the application receives the CN_QUERYDELTA notification code, the application is responsible for removing and inserting container records by using the CM_REMOVERECORD message and the CM_INSERTRECORD message, respectively.
Note:
The delta concept is intended for applications with large amounts of data, or several thousand records. Applications with smaller amounts of data are not required to use the delta function. The default delta value is 0.
The delta function is not available in the Icon view because it is intended for data displayed in a linear format.