YAJL (Objective-C Wrapper)

YAJL.framework is an Objective-C wrapper around the YAJL SAX-style JSON parser.

Download

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Install (Mac OS X)

There are two options. You can install it globally in /Library/Frameworks or with a little extra effort embed it with your project.

Installing in /Library/Frameworks

• Copy YAJL.framework to /Library/Frameworks/
• In the target Info window, General tab:
  • Add a linked library, under Mac OS X 10.5 SDK section, select YAJL.framework

Installing in your project

• Copy YAJL.framework to your project directory (maybe in MyProject/Frameworks/.)
• Add the YAJL.framekwork files (from MyProject/Frameworks/) to your target. It should be visible as a Linked Framework in the target.
• Under Build Settings, add @loader_path/../Frameworks to Runpath Search Paths
• Add New Build Phase | New Copy Files Build Phase.
  • Change the Destination to Frameworks.
  • Drag YAJL.framework into the the build phase
  • Make sure the copy phase appears before any Run Script phases

Install (iPhone)

• Add files (from static library build) to project.
• Under 'Other Linker Flags' in the Test target, add -ObjC and -all_load (So NSObject+YAJL category is loaded).

Usage

To parse JSON from an NSData (or NSString):

#import "NSObject+YAJL.h"

NSData *JSONData = [NSData dataWithContentsOfFile:@"example.json"];
NSArray *arrayFromData = [JSONData yajl_JSON];

NSString *JSONString = @"[\"Test\"]";
NSArray *arrayFromString = [JSONString yajl_JSON];

// With options and out error
NSError *error = nil;
NSArray *arrayFromString = [JSONString yajl_JSONWithOptions:YAJLParserOptionsAllowComments error:&error];

To generate JSON from an object:

#import "NSObject+YAJL.h"

NSDictionary *dict = [NSDictionary dictionaryWithObject:@"value" forKey:@"key"];
NSString *JSONString = [dict yajl_JSONString];

// Beautified with custon indent string
NSArray *array = [NSArray arrayWithObjects:@"value1", @"value2", nil];
NSString *JSONString = [dict yajl_JSONStringWithOptions:YAJLGenOptionsBeautify indentString:@"    "];

To use the streaming (or SAX style) parser, use YAJLParser. For higher level (document) streaming, see below.

NSData *data = [NSData dataWithContentsOfFile:@"example.json"];

YAJLParser *parser = [[YAJLParser alloc] initWithParserOptions:YAJLParserOptionsAllowComments];
parser.delegate = self;
[parser parse:data];
if (parser.parserError) {
	NSLog(@"Error:\n%@", parser.parserError);
}

parser.delegate = nil;
[parser release];

// Include delegate methods from YAJLParserDelegate
/*
- (void)parserDidStartDictionary:(YAJLParser *)parser;
- (void)parserDidEndDictionary:(YAJLParser *)parser;

- (void)parserDidStartArray:(YAJLParser *)parser;
- (void)parserDidEndArray:(YAJLParser *)parser;

- (void)parser:(YAJLParser *)parser didMapKey:(NSString *)key;
- (void)parser:(YAJLParser *)parser didAdd:(id)value;
*/

Parser Options

There are options when parsing that can be specified with YAJLParser#initWithParserOptions:.

• YAJLParserOptionsAllowComments: Allows comments in JSON
• YAJLParserOptionsCheckUTF8: Will verify UTF-8
• YAJLParserOptionsStrictPrecision: Will force strict precision and return integer overflow error, if number is greater than long long.

Streaming Example (Parser)

YAJLParser *parser = [[[YAJLParser alloc] init] autorelease];
parser.delegate = self;

// A chunk of data comes...
YAJLParserStatus status = [parser parse:chunk1];
// 'status' should be YAJLParserStatusInsufficientData, if its not finished
if (parser.parserError) ...;

// Another chunk of data comes...
YAJLParserStatus status = [parser parse:chunk2];
// 'status' should be YAJLParserStatusOK if its finished
if (parser.parserError) ...;

Usage (Document-style)

To use the document style, use YAJLDocument. Usage should be very similar to NSXMLDocument.

NSData *data = [NSData dataWithContentsOfFile:@"example.json"];
NSError *error = nil;
YAJLDocument *document = [[YAJLDocument alloc] initWithData:data parserOptions:0 error:&error];
// Access root element at document.root
NSLog(@"Root: %@", document.root);
[document release];

Streaming Example (Document)

YAJLDocument *document = [[YAJLDocument alloc] init];
document.delegate = self;

NSError *error = nil;
[document parse:chunk1 error:error];
[document parse:chunk2 error:error];

// You can access root element at document.root
NSLog(@"Root: %@", document.root);
[document release];

// Or via the YAJLDocumentDelegate delegate methods

- (void)document:(YAJLDocument *)document didAddDictionary:(NSDictionary *)dict { }
- (void)document:(YAJLDocument *)document didAddArray:(NSArray *)array { }
- (void)document:(YAJLDocument *)document didAddObject:(id)object toArray:(NSArray *)array { }
- (void)document:(YAJLDocument *)document didSetObject:(id)object forKey:(id)key inDictionary:(NSDictionary *)dict { }

Customized Encoding

To implement JSON encodable value for custom objects or override for existing objects, implement - (id)JSON;

For example:

@interface CustomObject : NSObject
@end

@implementation CustomObject

- (id)JSON {
  return [NSArray arrayWithObject:[NSNumber numberWithInteger:1]];
}

@end

Then:

CustomObject *customObject = [[CustomObject alloc] init];
NSString *JSONString = [customObject yajl_JSON];
// JSONString == "[1]";