Assembly: Microsoft.Synchronization.Files (in microsoft.synchronization.files.dll)
When a custom provider is the source provider and a FileSyncProvider object is the destination provider, the source provider must return an object that implements IFileDataRetriever object in its LoadChangeData method (LoadChangeData for simple providers).
When a custom provider is the destination provider and a FileSyncProvider object is the source provider, the destination provider will receive an IFileDataRetriever object in its SaveItemChange method. The destination provider can then use the IFileDataRetriever methods to get the file data from the source replica so that it can apply the change to the destination replica. For more information, see Synchronizing File Synchronization Provider with Other Providers.