D-32 Blog -

I wanted a simple way to persist my model changes without having any boilerplate code in the model classes. With this solution any model object just has to inherit from Model, that's it.

Every model object will observe its own properties and when a change occurs it will persisted. In this example everything just gets saved to disk. Obviously for bigger amounts of data the storage part would have to be done better.

For this to work, please add AutoCoding to your project.

Model.m:

@implementation Model {
    NSObject *_temp;
}

- (instancetype)init {
    if (self = [super init]) {
        [self modelSetup];
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder {
    if (self = [super initWithCoder:aDecoder]) {
        [self modelSetup];
    }
    return self;
}

- (void)modelSetup {
    NSDictionary *dict = [[self class] codableProperties];
    for (NSString *property in dict.allKeys) {
        [self addObserver:self forKeyPath:property options:NSKeyValueObservingOptionPrior context:nil];
    }
}

- (void)dealloc {
    NSDictionary *dict = [[self class] codableProperties];
    for (NSString *property in dict.allKeys) {
        [self removeObserver:self forKeyPath:property];
    }
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    id value = [object valueForKey:keyPath];
    if ([change[@"notificationIsPrior"] isEqualToNumber:@1]) {
        _temp = value;
    } else {
        if (![_temp isEqual:value]) {
#warning TODO
            // call some singelton here to save your data
        }
    }
}

@end

Self Storing Model

For this to work, please add AutoCoding to your project.