A file filter is a dynamic-link library (DLL) that controls the transfer of data between the desktop computer and the Windows CE-based device. File filters are used by the Windows CE Services application on the desktop computer to automatically convert files as they are transferred.
File formats used by the Windows CE operating system and Windows CE-based applications are generally different from those of the corresponding Windows-based applications. For example, Pocket Word does not support OLE compound files. Windows CE Services automatically adjusts file formats as files are transferred between the desktop computer and the Windows CE-based device.
Some of the common filters provided with Windows CE Services include:
You can extend the file-filtering capability of Windows CE Services by defining your own application-specific filters. This section describes file filters and the interfaces used to create them.
Implementing a file filter is similar for importing and exporting files. The only differences are in the registry settings and in how the body of the file filter — the converter function — changes data. The examples in this section demonstrate the procedure for importing files, but typically you would write a converter function that handles both importing and exporting, using dual registry settings that indicate both the import and export functionality.
Note The words "importing" and "exporting" in this chapter are from the perspective of the Windows CE-based device. Thus, importing a file with a file filter transfers a file from the desktop computer to the device, whereas exporting a file with a file filter transfers a file from the device to the desktop.