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nicklockwood / AutoCoding

AutoCoding is a category on NSObject that provides automatic support for NSCoding and NSCopying to every object.
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Purpose

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

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.

Installation

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

Security

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.

NSCopying

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.

Tips

  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
{
    //pre-initialisation
    [super setWithCoder:coder];
    //post-initialisation
}

    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 2.2.3

Version 2.2.2

Version 2.2.1

Version 2.2

Version 2.1

Version 2.0.3

Version 2.0.2

Version 2.0.1

Version 2.0

Version 1.3.1

Version 1.3

Version 1.2.1

Version 1.2

Version 1.1.2

Version 1.1.1

Version 1.1

Version 1.0