Does anyone have example code using encodeBytes:length:forKey:? - ios

Question

I need it for my NSCoder classes apparently and it would be useful if I can see a real example of this and its corresponding method.
The reason I feel I need it is when my method tries to encodeObject for an NSString*, it complains saying:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -encodeBytes:length:forKey: only defined for abstract class. Define -[JSONEncoder encodeBytes:length:forKey:]!'
Thanks.
The method in JSONEncoder: (https://github.com/ontometrics/JSONCoding) I couldn't get the static library thing to work, so I'm trying to work directly with the code.
- (void)encodeObject:(id)object {
[self push:object];
[object encodeWithCoder:self];
finalJSONObject = [NSDictionary dictionaryWithObject:[self topObject] forKey:[[[object class] description] camelcaseString]];
[self pop];
}

Answer 1

I think that the JSONEncoder is mainly meant to encode objects from custom classes (which must implement the NSCoding protocol). For example, if you define a class Person with a string property:
#interface Person : NSObject <NSCoding>
#property(strong, nonatomic) NSString *name;
#end
#implementation Person
- (id)initWithCoder:(NSCoder *)coder {
if ((self = [super init])) {
self.name = [coder decodeObjectForKey:#"name"];
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)coder {
[coder encodeObject:self.name forKey:#"name"];
}
#end
then you can encode an object of this class without problems using JSONEncoder:
JSONEncoder *encoder = [JSONEncoder encoder];
Person *obj = [[Person alloc] init];
obj.name = #"John";
[encoder encodeObject:obj];
NSString *json = [encoder json];
NSLog(#"%#", json);
// Output: {"person":{"name":"John"}}
It works also with some "plain" Foundation types, e.g. with NSNumber, but the output is not very "nice", and I am not sure if JSONEncoder is meant to be used like that:
JSONEncoder *encoder = [JSONEncoder encoder];
NSNumber *obj = #1234;
[encoder encodeObject:obj];
NSString *json = [encoder json];
NSLog(#"%#", json);
// Output: {"__NSCFNumber":{"NS.intval":1234}}
In this case, the encodeInt64:forKey: method of JSONEncoder is called internally.
However, as you noticed, it does not work with NSString:
JSONEncoder *encoder = [JSONEncoder encoder];
NSString *obj = #"Hello world";
[encoder encodeObject:obj];
// Exception: *** -encodeBytes:length:forKey: only defined for abstract class. Define -[JSONEncoder encodeBytes:length:forKey:]!
The reason for the exception is that NSString is NSCoding compliant, but it uses the -encodeBytes:length:forKey: of the coder, and JSONEncoder does not implement this method.
Implementing that method is not too difficult, this is a quick-and-dirty attempt:
- (void)encodeBytes:(const uint8_t *)bytesp length:(NSUInteger)lenv forKey:(NSString *)key
{
NSString *s = [[NSString alloc] initWithBytes:bytesp length:lenv encoding:NSUTF8StringEncoding];
[self setObject:s forKey:key];
}
If you add this code to "JSONEncoder.m", then you can encode a plain NSString without getting an exception, the result looks like this:
{"__NSCFConstantString":{"NS.bytes":"Hello world"}}
But again, I am not sure if JSONEncoder is meant to be used like this.