AutoCoding 2.2.3

AutoCoding 2.2.3

LangLanguage Obj-CObjective C
License zlib
ReleasedLast Release Oct 2017

Maintained by Nick Lockwood.

  • By
  • Nick Lockwood


AutoCoding is a category on NSObject that provides automatic support for NSCoding to any object. This means that rather than having to implement the initWithCoder: and encodeWithCoder: methods yourself, all the model classes in your app can be saved or loaded from a file without you needing to write any additional code.

Of course no automated system can read your mind, so AutoCoding does place certain restrictions on how you design your classes; For example, you should avoid using structs that are not already NSCoding-compliant via NSValue.

Use of AutoCoding is by no means and all-or-nothing decision. You are free to implement your own NSCoding or NSCopying methods on any class in your project and they will simply override the automatically generated methods.

Supported OS & SDK Versions

  • Supported build target - iOS 9.3 / Mac OS 10.11 (Xcode 7.3, Apple LLVM compiler 7.1)
  • Earliest supported deployment target - iOS 7.0 / Mac OS 10.10
  • Earliest compatible deployment target - iOS 4.3 / Mac OS 10.6

NOTE: 'Supported' means that the library has been tested with this version. 'Compatible' means that the library should work on this OS version (i.e. it doesn't rely on any unavailable SDK features) but is no longer being tested for compatibility and may require tweaking or bug fixes to run correctly.

ARC Compatibility

AutoCoding is compatible with both ARC and non-ARC compile targets.

Thread Safety

AutoCoding is fully thread-safe.


To use the AutoCoding category in your project, just drag the AutoCoding.h and .m files into your project.


As of version 2.0, AutoCoding supports the NSSecureCoding protocol automatically, and returns YES for the +supportsSecureCoding method for all objects by default. In addition to this, assuming you do not override +supportsSecureCoding to return NO, AutoCoding will automatically throw an exception when attempting to decode a class whose type doesn't match the property it is being assigned to. This makes it much harder for a malicious party to craft an NSCoded file that, when loaded by your app, will cause it to execute code that you didn't intend it to.


As of version 2.1, NSCopying is no longer implemented automatically, as this caused some compatibility problems with Core Data NSManagedObjects. If you wish to implement copying, this can be done quite easily by looping over the codableProperties keys and copying those properties individually to a new instance of the object (as follows):

- (id)copyWithZone:(id)zone
    id copy = [[[self class] alloc] init];
    for (NSString *key in self.codableProperties)
        [copy setValue:[self valueForKey:key] forKey:key];
    return copy;

In order to properly support NSCopying, you should also override the -hash and -isEqual: methods for any object you intend to use with copying, so that a copied object has the same hash value and is equal to the original.


  1. To exclude certain properties of your object from being encoded, you can do so in any of the following ways:

    • Only use an ivar, without declaring a matching @property.
    • Change the name of the ivar to something that is not KVC compliant (i.e. not the same as the property, or the property name with an _ prefix). You can do this using the @synthesize method, e.g. @synthesize foo = unencodableFoo;
    • Override the +codableProperties method
  2. If you want to perform initialisation of the class post or prior to the properties being loaded via NSCoding, override the setWithCoder: method and call the super-implementation before or after applying your own logic, like this:

    - (void)setWithCoder:(NSCoder *)coder
        [super setWithCoder:coder];

    Note that unlike in previous versions, the init method is not called when using initWithCoder:.

  3. If you want to perform some cleanup or post-processing or substitute a different object after the object has been loaded via NSCoding, you can use the awakeAfterUsingCoder: method, which is defined in the NSObject class reference.

  4. You can add additional coding/decoding logic by overriding the setWithCoder: and/or encodeWithCoder: methods. As long as you call the [super ...] implementation, the auto-coding will still function.

  5. If you wish to substitute a different class for properties of a given type - for example if you have changed the name of a class but wish to retain compatibility with files saved using the old class name, you can substitute a different class for a given name by using the [NSKeyedUnArchiver setClass:forClassName:] method.

  6. If you have properties of a type that doesn't support NSCoding (e.g. a struct), and you wish to code them yourself by applying a conversion function, mark the property as unecodable by changing its ivar name and override the setWithCoder: and encodeWithCoder: methods (remembering to call the super-implementations of those methods to automatically load and save the other properties of the object). Like this:

    @synthesize uncodableProperty = noencode_uncodableProperty; //non-KVC-compliant name
    - (void)setWithCoder:(NSCoder *)coder
        [super setWithCoder:coder];
        self.uncodableProperty = DECODE_VALUE([coder decodeObjectForKey:@"uncodableProperty"]);
    - (void)encodeWithCoder:(NSCoder *)coder
        [super encodeWithCoder:coder];
        [coder encodeObject:ENCODE_VALUE(self.newProperty) forKey:@"uncodableProperty"];
  7. If you have changed the name of a property, but want to check for the existence of the old key name for backwards compatibility, override the setWithCoder: method and add a check for the old property as follows:

    - (void)setWithCoder:(NSCoder *)coder
        [super setWithCoder:coder];
        self.newProperty = [coder objectForKey:@"oldProperty"] ?: self.newProperty;
  8. If you have changed the name of a property, but want to load and save it using the old key name for backwards compatibility, give the new property a non-KVC-compliant ivar name and override the setWithCoder:/encodeWithCoder: methods to save and load the property using the old name (remembering to call the super-implementations of those methods to automatically load and save the other properties of the object). Like this:

    @synthesize newProperty = noencode_newProperty; //non-KVC-compliant name
    - (void)setWithCoder:(NSCoder *)coder
        [super setWithCoder:coder];
        self.newProperty = [coder objectForKey:@"oldProperty"];
    - (void)encodeWithCoder:(NSCoder *)coder
        [super encodeWithCoder:coder];
        [coder encodeObject:self.newProperty forKey:@"oldProperty"];

Release Notes

Version 2.2.2

  • Fixed warnings on latest Xcode
  • Added nullability and lightweight generics
  • Moved method and property documentation into the header file

Version 2.2.1

  • Added missing import, required on Xcode 6.x

Version 2.2

  • Now supports @dynamic properties, allowing AutoCoding to be used with NSManagedObjects
  • Added support for additional integer types
  • Fixed unit tests

Version 2.1

  • Removed automatic NSCopying implementation (see README for details)
  • The +codableProperties method will no longer include properties whose ivars are not KVC compliant, even if they are readwrite. This makes it easier to mark readwrite properties as uncodable without needing to override methods
  • The +uncodableProperties method is now deprecated
  • dictionaryRepresentation method will now no longer include NSNull entries for nil values (these will simply be omitted from the result instead)
  • Now complies with the -Weverything warning level

Version 2.0.3

  • Now complies with the -Wextra warning level

Version 2.0.2

  • Fixed longstanding issue where uncodableProperties / uncodableKeys was ignored for readonly properties.

Version 2.0.1

  • Fixed bug where AutoCoding's NSCopying implementation was not compatible with properties using copy semantics due to lack of a copyWithZone: implementation.
  • Now returns YES for respondsToSelector:@selector(copyWithZone:).

Version 2.0

  • AutoCoding now implements the NSSecureCoding protocol automatically
  • AutoCoding now detects property types automatically and throws an exception by default if encoded classes to not match the expected type
  • Autocoding 2.0 is data-compatible with previous releases, but may require code changes when upgrading.

Version 1.3.1

  • Fixed issue with CoreData where AutoCoding's copyWithZone: implementation conflicted with NSManagedObjects
  • Due to changes in the automatic NSCopying implementation, calling [super copyWithZone:] will no longer work. If you need to do this, override the copy method and call [super copy] instead
  • Added Podspec file

Version 1.3

  • AutoCoding no longer attempts to encode virtual properties. Only ivar-backed properties will be encoded
  • Added dictionaryRepresentation method for quickly accessing all properties of a class
  • The codableKeys and uncodableKeys methods are now class methods, allowing them to be used more easily in factory methods
  • The class-level codable/uncodableKeys methods now only return the properties for the class on which they are called, not all of its superclasses as well
  • It is no longer necessary to call [super codableKeys] or [super uncodableKeys] and merge arrays when overriding the codableKeys or uncodableKeys class methods on a subclass (overriding the codableKeys instance method is not recommended)

Version 1.2.1

  • writeToFile:atomically: method now returns a BOOL to indicate success
  • Changed category file names

Version 1.2

  • Read-only properties can now be copied and coded as long as they have a KVC compliant ivar (i.e. one whose name matches the property or the property with the _ prefix)
  • initWithCoder: no longer calls [self init], in compliance with Apple docs
  • codableKeys method now uses caching for better performance
  • Exposed previously private setWithCoder: method used by BaseModel library

Version 1.1.2

  • Switched constructor to return new type-safe instancetype instead of id, making it easier to use dot-syntax property accessors on loaded instances.

Version 1.1.1

  • Read-only properties are now excluded from codableKeys
  • Added unit tests

Version 1.1

  • Added automatic NSCopying implementation
  • writeToFile now obeys the useAuxiliaryFile parameter

Version 1.0

  • Initial release