The Import/Export Library: 1.1 Impex Basics: The Impex Objects

There are two Impex objects which applications need to know about: ImportControl and ExportControl. These objects are both subclassed off of ImportExportClass , which provides some functionality needed for both objects; however, all this functionality is internal, so you can ignore this class. (No one should ever create an ImportExport object, and it has no instance data which applications may set.) ImportExportClass is itself subclassed from GenControlClass ; therefore, ImportControl and ExportControl objects inherit all the functionality of controllers.

Applications will generally have one ImportControl and one ExportControl object. Applications may put these in different places; for example, some will place both of these on the File menu, while others may put them in the "Open" or "Save As" dialog boxes. Applications should decide this based on how they think the user will be using the import and export capabilities.

The ImportControl and ExportControl objects communicate with the application by sending messages. The ImportControl object sends a message to its recipient near the end of the Import process, when it has translated a file into a VM chain for the application to copy. The ExportControl object sends a message near the beginning of the export process, instructing the application to create a VM chain for the application to export. In both cases the message sent and the recipient are set by the application. Most applications will have the messages sent to their process arguments; however, applications which use the object model of document control may want to have the messages sent to the target object.

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1.2 How the Impex Objects Work