I just got core data migration working via NSMigrationManager. According to Apple doc:
migrationProgress Returns a number from 0 to 1 that indicates the proportion of completeness of the migration.
- (float)migrationProgress
Return Value A number from 0 to 1 that indicates the proportion of completeness of the migration. If a migration is not taking place, returns 1.
Special Considerations You can observe this value using key-value observing.
I used KVO getting notified the % of migration progress, but I am wondering if "migrationProgress" really is a getter? If it is, why didn't Apple document it as a "readonly" property, to make it clear for developer to use?