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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.

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

AutoCoding is also designed to work hand-in-hand with the BaseModel library (https://github.com/nicklockwood/BaseModel) to form the basis for building a powerful model hierarchy for your project with minimal effort.

Supported OS & SDK Versions

  • Supported build target - iOS 5.0 / Mac OS 10.7 (Xcode 4.2, Apple LLVM compiler 3.0)
  • Earliest supported deployment target - iOS 4.3 / Mac OS 10.6
  • Earliest compatible deployment target - iOS 3.0 / 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 iOS 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 NSObject+AutoCoding files into your project.

Category methods

The NSObject(AutoCoding) category extends NSObject with the following methods. Since this is a category, every single Cocoa object, including AppKit/UIKit objects and BaseModel instances inherit these methods.

- (NSArray *)codableKeys;

This method returns an array containing the names of all the properties of the object that will be automatically saved and loaded when the object is archived using NSKeyedArchiver/Unarchiver. This array is automatically generated by scanning the properties defined in the class definition at runtime. It is not normally necessary to override this method; If you wish to exclude certain properties from the serialisation process, you can return them in the uncodableKeys method and they will be automatically removed from this array.

- (NSArray *)uncodableKeys;

This method can be used to exclude certain properties from automatic coding without having to override the codableKeys method or implement the initWithCoder: and encodeWithCoder: methods yourself from scratch. The default return value of this method is nil. Implement the method and return an array containing the names of any properties you wish to exclude.

+ (id)objectWithContentsOfFile:(NSString *)path;

This attempts to load the file using the following sequence: 1) If the file is an NSCoded archive, load the root object and return it, 2) If the file is an ordinary Plist, load and return the root object, 3) Return the raw data as an NSData object. If the de-serialised object is not a subclass of the class being used to load it, an exception will be thrown (to avoid this, call the method on NSObject instead of a specific subclass).

- (void)writeToFile:(NSString *)filePath atomically:(BOOL)useAuxiliaryFile;

This attempts to write the file to disk. This method is overridden by the equivalent methods for NSData, NSDictionary and NSArray, which save the file as a human-readable XML Plist rather than an binary NSCoded Plist archive, but the objectWithContentsOfFile: method will correctly de-serialise these again. For any other object it will serialise the object using the NSCoding protocol and write out the file as a NSCoded binary Plist archive.

Tips

  1. If you want to perform initialisation of the class prior to the properties being loaded via NSCoding, you can use the init method, which is called before the decoding occurs.

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

  3. You can add additional coding/decoding logic by overriding the initWithCoder: and/or encodeWithCoder: methods. As long as you call the [super ...] implementation, the auto-coding will still function. If you are using the BaseModel superclass, you should override the setWithCoder: method instead of initWithCoder:.

  4. 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.