Palm OS Programming, 2nd Edition

Custom File Formats

If you are going to support your own file format in your conduit, then you’ll need to override two routines in your subclass of CPcMgr: StoreDB and RetrieveDB. The first will save the in-memory list of records to your format. The second will read from your format, creating records and adding them to the in-memory list.

We’d always suggest writing StoreDB first, if for no other reason than you can test it without having written RetrieveDB. This is because the Generic Conduit Framework won’t call your RetrieveDB routine if there’s no file in the user’s directory. Therefore, as long as you keep deleting the file between syncs, you can test your StoreDB to your heart’s content.

Note that when StoreDB is called, the sync has already taken place and all of the following actions have occurred:

• Modified records have been copied between the handheld and the in-memory list (maintained by the Generic conduit).

• Records whose deleted bits were set have been deleted.

• All the records are clean (the dirty and deleted bits are not set).

The StoreDB Routine

Example 16-1 shows the outline of a StoreDB routine.

Example 16-1. A typical StoreDB (emphasized code is specific to your conduit)

long CMyConduitPcMgr::StoreDB(void) { if ( !m_bNeedToSave) { // If no changes, don't waste time saving. return 0; } long err = Open( ); if (err) return GEN_ERR_UNABLE_TO_SAVE; for (DWORD dwIndex = 0; (dwIndex < m_dwMaxRecordCount) && (!err); dwIndex++) { if (!m_pRecordList[dwIndex]) continue; ...