Encoding custom classes using yajl-objc - iphone

Question

Summary. Based on some benchmarks, I chose yajl-objc for my iPhone JSON parser. I was testing it with an arbitrary custom class (one NSNumber and two NSString properties). If I created an NSDictionary with key-value pairs matching the class properties, I could encode the dictionary with [dictionary yajl_JSON]. When I tried directly encoding an instance of the custom class with [custom yajl_JSON], I got this compiler error:
Terminating app due to uncaught exception 'YAJLParsingUnsupportedException', reason: 'Object of type (Custom) must implement dataUsingEncoding: to be parsed'.
I got the error even when I implemented - (id)JSON (as suggested in the yajl-objc readme). I know my code, not the library, is the problem. I just can't figure out what I'm doing wrong.
Details. My Custom.h:
#import
#interface Custom : NSObject {
NSString *name;
NSNumber *number;
NSString *text;
}
#property (nonatomic, copy) NSString *name;
#property (nonatomic, copy) NSNumber *number;
#property (nonatomic, copy) NSString *text;
#end
In Custom.m, I defined an - (id)JSON method per the yajl-obj documentation:
- (id)JSON
{
NSDictionary *jsonDictionary =
[[[NSMutableDictionary alloc] init] autorelease];
[jsonDictionary setValue:name forKey:#"name"];
[jsonDictionary setValue:number forKey:#"number"];
[jsonDictionary setValue:text forKey:#"text"];
return jsonDictionary;
}
Creating a key-value matched dictionary and encoding it works fine:
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setValue:self.custom.name forKey:#"name"];
[dict setValue:self.custom.number forKey:#"number"];
[dict setValue:self.custom.text forKey:#"text"];
NSString *JSONString = [dict yajl_JSON];
But when I call NSString* JSONString = [custom yajl_JSON]; here's the compiler error and stack trace I get:
*** Terminating app due to uncaught exception 'YAJLParsingUnsupportedException', reason: 'Object of type (Custom) must implement dataUsingEncoding: to be parsed'
*** Call stack at first throw:
(
0 CoreFoundation 0x0266bb99 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x027bb40e objc_exception_throw + 47
2 CoreFoundation 0x02624238 +[NSException raise:format:arguments:] + 136
3 CoreFoundation 0x026241aa +[NSException raise:format:] + 58
4 TestCustomFileFormat 0x00005151 -[NSObject(YAJL) yajl_JSONWithOptions:error:] + 206
5 TestCustomFileFormat 0x00005212 -[NSObject(YAJL) yajl_JSON:] + 49
6 TestCustomFileFormat 0x00005249 -[NSObject(YAJL) yajl_JSON] + 49
7 TestCustomFileFormat 0x00002eba -[TestViewController loadInstruction] + 758
8 TestCustomFileFormat 0x00002aa5 -[TestViewController viewDidLoad] + 77
9 UIKit 0x0037585a -[UIViewController view] + 179
10 TestCustomFileFormat 0x00002377 -[TestCustomFileFormatAppDelegate application:didFinishLaunchingWithOptions:] + 112
11 UIKit 0x002cc6a7 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1163
12 UIKit 0x002ceb30 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 346
13 UIKit 0x002d8b6c -[UIApplication handleEvent:withNewEvent:] + 1958
14 UIKit 0x002d12bc -[UIApplication sendEvent:] + 71
15 UIKit 0x002d613f _UIApplicationHandleEvent + 7672
16 GraphicsServices 0x02f4b81e PurpleEventCallback + 1578
17 CoreFoundation 0x0264cff4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 52
18 CoreFoundation 0x025ad807 __CFRunLoopDoSource1 + 215
19 CoreFoundation 0x025aaa93 __CFRunLoopRun + 979
20 CoreFoundation 0x025aa350 CFRunLoopRunSpecific + 208
21 CoreFoundation 0x025aa271 CFRunLoopRunInMode + 97
22 UIKit 0x002ce3ed -[UIApplication _run] + 625
23 UIKit 0x002da272 UIApplicationMain + 1160
24 TestCustomFileFormat 0x000022e4 main + 102
25 TestCustomFileFormat 0x00002275 start + 53
)
terminate called after throwing an instance of 'NSException'
In response, I tried conforming to NSCoding, used NSKeyedArchiver to create an NSMutableData representation of the class instance and called [data yajl_JSON], but that didn't work either.
I know I'm missing something simple, but I'm too stupid to figure it out.

Answer 1

You’re doing it the wrong way around. To create a JSON string from an object you use yajl_JSONString. yail_JSON is there to take a string (or a NSData object or something that can be archived) and parse that into objects.