Question

I’m working with django-piston and parsing that JSON output in Objective-C, but having some trouble because the output doesn’t contain any top-level labels. Every example I’ve come across has the data parsed into a dictionary, then generating an array based on objectForKey:@”foo” but in my case, I have no top-level text to parse based on.

Here’s the JSON generated by Piston:

[
{
    "text": "Pain Intensity", 
    "question_number": 1, 
    "id": 1
}, 
{
    "text": "Personal Care (washing, dressing, etc.)", 
    "question_number": 2, 
    "id": 2
}, 
{
    "text": "Lifting", 
    "question_number": 3, 
    "id": 3
}, 
{
    "text": "Walking", 
    "question_number": 4, 
    "id": 4
}, 
{
    "text": "Sitting", 
    "question_number": 5, 
    "id": 5
}

]

What I’d like to do is end up with an array of objects containing an id, text and question number property.

Any advice?

Answer 1

IF you are using iOS 5 (for an iOS app) or OS 10.7 (for a Mac app), then the NSJSONSerialization class is built right in:

NSArray *parsedJSON = [JSONObjectWithData:myData options:myOptions error:&error];

This will work whenever the myData object (an NSData instance) contains a valid JSON string using one of the supported JSON encodings, and the top-level element of that JSON string is an array as it is in your example.

When you do this with your example JSON string, you should get an NSArray containing 5 dictionaries. So you could do something like this:

NSMutableArray *newArray = [[NSMutableArray alloc] init];
for (int i = 0; i < [parsedJSON count]; i++) {
    MyClass *newObject = [[MyClass alloc] init];
    NSDictionary *questionDict = [parsedJSON objectAtIndex:i];
    [myObject setText:[questionDict objectForKey:@"text"]];
    [myObject setQuestionNumber:[questionDict objectForKey:@"question_number"]];
    [myObject setID:[questionDict objectForKey:@"id"]];
    [newArray addObject:newObject];
}

The above assumes you’ve defined a class called MyClass with properties called text, questionNumber, and id.