GBJSON

This code provides a way to parse a deserialized JSON object and to match it with Objective-C classes.

Who Can Use It

OSX and iOS developers who are using ARC (so over iOS 5.0).

Description

Long story short

I'm trying to create some kind of GSON (Android) parser for iOS 5.0 (and over)

Long story long

As you probably know, since iOS 5.0 it's possible to serialize objects using JSON easily. So it's quite simple to get a JSON NSData representation of an object using:

[NSJSONSerialization dataWithJSONObject:jsonObject options:NSJSONWritingPrettyPrinted error:&jsonError];

Similarly it's possible to get a JSON object from it's NSData representation using:

[NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:&jsonError];

But the problem of this last method is that it's matching all objects using NSDictionary. So GBJSON tries to get rid of this by using the result of JSONObjectWithData: as an input. Then it tries to match dictionaries with given classes by using variables identifiers in JSON stream.

For example if you have a string in your JSON stream like: "firstName": "John"

The program will try to find the variable firstName in a given class and if it finds it, it will set its value to "John".

How To Use

Initial steps

It's quite easy to use this parser. You need to deserialize your JSON stream first and then you need to call GBJSON with 3 things:

The JSON object you deserialized
The Class of the first object (could be an NSArray)
A provider (discribed in "Provider implementation")

#import "GBJSON.h"

...

{

	...

	// Get your data
	NSData *jsonData = ...;

	// Get your JSON object
	id jsonObject = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:&jsonError];

	// Check jsonError and that jsonObject != nil

	// Then call GBJSON
	MyClass *myObject = [GBJSON parseJSONObject:jsonObject usingClass:[MyClass class] provider:self];

	...

}

It will log errors if there are problems or it will just initialize all variables of MyClass that are in your JSON stream.

Provider implementation

There are 3 issues to fully parse a deserialized JSON:

1- Objective-C arrays are not strongly typed
2- JSON stream may contain string values for non-string object (e.g. NSDate)
3- JSON stream may contain string values for scalar variables or enums

That's why in GBJSON.h there is a GBJSONProvider protocol with the 3 following functions:

(Class)getClassForElementsInArrayNamed:(NSString *)arrayName;
(id)getObjectForClass:(Class)aClass fromString:(NSString *)aString;
(NSNumber*)getNSNumberForString:(NSString *)aString;

A small example will be perfect to explain how to implement these functions. Imagine that a webservice is giving you the following JSON.

{
	"name":"Robert Allen Zimmerman",
	"number":"+353600000000",
	"birthDate":"19410524000000",
	"gender":"male",
	"hasFans":"true",
	"contacts":[
	{
		"name":"Bob",
		"number":"+353600000000"
	},
	{
		"name":"Dylan",
		"number":"+33699999999"
	}
	]
}

And that you want to parse this JSON to fit with the following class.

#import <Foundation/Foundation.h>

typedef NS_ENUM(NSInteger, GenderType)
{
    GenderTypeMale,
    GenderTypeFemale,
    GenderTypeOther
};

@interface Person : NSObject

@property (strong, nonatomic) NSString *name;
@property (strong, nonatomic) NSString *number;
@property (strong, nonatomic) NSDate *birthDate;
@property (assign, nonatomic) GenderType gender;
@property (assign, nonatomic) BOOL hasFans;
@property (strong, nonatomic) NSArray *contacts;

@end

The first problem you will face will be the "birthDate" because it's a string in the JSON. To solve this issue GBJSON will call the function getObjectForClass:fromString: So your provider should implement it like the following.

- (id)getObjectForClass:(Class)aClass fromString:(NSString *)aString
{
	if (aClass == [NSDate class])
	{
		NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
		[dateFormatter setDateFormat:@"yyyy-MM-dd"];
		return [dateFormatter dateFromString:aString];
	}

	// Don't forget to return nil by default
	return nil;
}

Then you will have issues with "gender" and "hasFans" variables. getNSNumberForString: will help you to get rid of these two. Implement the following in your provider.

- (NSNumber*)getNSNumberForString:(NSString *)aString
{
	if ([aString isEqualToString:@"true"])
	{
		return [NSNumber numberWithBool:YES];
	}
	else if ([aString isEqualToString:@"false"])
	{
		return [NSNumber numberWithBool:NO];
	}
	else if ([aString isEqualToString:@"male"])
	{
		return [NSNumber numberWithInteger:GenderTypeMale];
	}
	else if ([aString isEqualToString:@"female"])
	{
		return [NSNumber numberWithInteger:GenderTypeFemale];
	}
	else if ([aString isEqualToString:@"other"])
	{
		return [NSNumber numberWithInteger:GenderTypeOther];
	}

	// Don't forget to return nil by default
	return nil;
}

Finally you will have an issue with "contacts" because in Objective-C arrays are not strongly-typed. So it's hard for the parser to know the type of objects inside an array. But the provider should have this information. That's why GBJSON will ask the provider to getClassForElementsInArrayNamed:. So implement the following in your provider.

- (Class)getClassForElementsInArrayNamed:(NSString *)arrayName
{
	if ([arrayName isEqualToString:@"contacts"])
	{
		return [Person class];
	}

	// Don't forget to return nil by default
	return nil;
}

For the moment it's still in experimental stage and I guess that some cases are not supported (like NSDictionary inside Objective-C objects). So just let me know if you have issues and I will try to find solutions ;)

Future Enhancements

Allow users to use NSDictionary variables.

Licenses

The source code is licensed under the Apache License V2.0.

bohrgu/GBJSON