Replace all NSNull objects in an NSDictionary

Question

I'm curious, I currently have an NSDictionary where some values are set to an NSNull object thanks to the help of json-framework.

The aim is to strip all NSNull values and replace it with an empty string.

I'm sure someone has done this somewhere? No doubt it is probably a four liner and is simple, I am just far too burnt out to figure this out on my own.

Answer 1

I have tested Stakenborg solution. It works well, but it has following problem. If some object is expected to be number, for instance, converting it to NSNull can be a source of error. I have create a new method to directly remove the NSNull entries. This way you only have to check that correspondant key exists.

Add in NSDictionary+NullReplacement

- (NSDictionary *)dictionaryByRemovingNulls{
    const NSMutableDictionary *replaced = [self mutableCopy];
    const id nul = [NSNull null];
    
    for (NSString *key in self) {
        id object = [self objectForKey:key];
        if (object == nul) [replaced removeObjectForKey:key];
        
        else if ([object isKindOfClass:[NSDictionary class]]) [replaced setObject:[object dictionaryByRemovingNulls] forKey:key];
        else if ([object isKindOfClass:[NSArray class]]) [replaced setObject:[object arrayByRemovingNulls] forKey:key];
    }
    return [NSDictionary dictionaryWithDictionary:[replaced copy]];
}

And in NSArray+NullReplacement

- (NSArray *)arrayByRemovingNulls {
    NSMutableArray *replaced = [self mutableCopy];
    const id nul = [NSNull null];

    for (int idx = [replaced count]-1; idx >=0; idx--) {
        id object = [replaced objectAtIndex:idx];
        if (object == nul) [replaced removeObjectAtIndex:idx];
        else if ([object isKindOfClass:[NSDictionary class]]) [replaced replaceObjectAtIndex:idx withObject:[object dictionaryByRemovingNulls]];
        else if ([object isKindOfClass:[NSArray class]]) [replaced replaceObjectAtIndex:idx withObject:[object arrayByRemovingNulls]];
    }
    return [replaced copy];
}