storedValueForKey:

Discussion 解説

This method is used when the value is retrieved for storage in an object store (generally, this storage is ultimately in a database) or for inclusion in a snapshot. The default implementation is similar to the implementation of valueForKey:, but it resolves key with a different method/instance variable search order:

1. Searches for a private accessor method based on key (a method preceded by an underbar). For example, with a key of “lastName”, storedValueForKey: looks for a method named _getLastName or _lastName.

2. If a private accessor is not found, searches for an instance variable based on key and returns its value directly. For example, with a key of “lastName”, storedValueForKey: looks for an instance variable named _lastName or lastName.

3. If neither a private accessor nor an instance variable is found, storedValueForKey: searches for a public accessor method based on key. For the key “lastName”, this would be getLastName or lastName.

4. If key is unknown, storedValueForKey: calls handleTakeValue:forUnboundKey:.

This different search order allows an object to bypass processing that is performed before returning a value through a public API. However, if you always want to use the search order in valueForKey:, you can implement the class method useStoredAccessor to return NO. And as with valueForKey:, you can prevent direct access of an instance variable with the class method accessInstanceVariablesDirectly.