Parsing JSON file using JSONKit - objective-c

Question

I am constructing a tuning fork app. The fork should allow up to 12 preset pitches.
Moreover, I wish to allow the user to choose a theme. Each theme will load a set of presets (not necessary to use all of them).
My configuration file would look something like this*:
theme: "A3"
comment: "An octave below concert pitch (ie A4 440Hz)"
presets: {
A3 220Hz=220.0
}
// http://en.wikipedia.org/wiki/Guitar_tuning
theme: "Guitar Standard Tuning"
comment:"EADGBE using 12-TET tuning"
presets: {
E2=82.41
A2=110.00
D3=146.83
G3=196.00
B3=246.94
E4=329.63
}
theme: "Bass Guitar Standard Tuning"
comment: "EADG using 12-TET tuning"
presets: {
E1=41.204
A2=55.000
D3=73.416
G3=97.999
}
...which need to be extracted into some structure like this:
#class Preset
{
NSString* label;
double freq;
}
#class Theme
{
NSString* label;
NSMutableArray* presets;
}
NSMutableArray* themes;
How do I write my file using JSON? ( I would like to create a minimum of typing on the part of the user -- how succinct can I get it? Could someone give me an example for the first theme? )
And how do I parse it into the structures using https://github.com/johnezang/JSONKit?

Answer 1

Here's a valid JSON example based on your thoughts:
[
{
"name": "Guitar Standard Tuning",
"comment": "EADGBE using 12-TET tuning",
"presets": {
"E2": "82.41",
"A2": "110.00",
"D3": "146.83",
"G3": "196.00",
"B3": "246.94",
"E4": "329.63"
}
},
{
"name": "Bass Guitar Standard Tuning",
"comment": "EADG using 12-TET tuning",
"presets": {
"E1": "41.204",
"A1": "55.000",
"D2": "73.416",
"G2": "97.999"
}
}
]
Read a file and parse using JSONKit:
NSData* jsonData = [NSData dataWithContentsOfFile: path];
JSONDecoder* decoder = [[JSONDecoder alloc]
initWithParseOptions:JKParseOptionNone];
NSArray* json = [decoder objectWithData:jsonData];
After that, you'll have to iterate over the json variable using a for loop.

Answer 2

Using the parser in your question and assuming you have Simeon's string in an NSString variable. Here's how to parse it:
#import "JSONKit.h"
id parsedJSON = [myJSONString objectFromJSONString];
That will give you a hierarchy of arrays and dictionaries that you can walk to get your Preset and Theme objects. In the above case, you would get an array with two dictionaries each with a name, comment and presets key. The first two will have NSString values and the third (presets) will have a dictionary as it's value with the note name as keys and the frequencies as values (as NSString objects).