Converting a JSON string into NSDictionary

Question

I'm trying to build an app in which people can order goods from different stores. I am totally new to programming, and I thought building a project like this would be a good way to learn it.

I'm stuck at the part of my app where a user can search for a company (on company name, location, or both) in my database. The database returns a JSON string, containing the company name and location for all found companies, which looks like this:

{"companyName":"testcompany_1","companyCity":"Tiel"},  
{"companyName":"tectcompany_2","companyCity":"Tiel"}

So far so good!

now I want to turn this JSON string, which is an NSString, into an NSDictionary, in order to display the names and locations of the found companies in a tableView. This is where I get stuck.

I have been searching through StackOverflow, google, etcetera, and I have tried several ways to do this, for example:

• Convert NSString to NSDictionary separated by specific character
• Convert JSON feed to NSDictionary

Since none of the tutorials/answers is saw really solves my problem, I tried to make something out of them myself, and this is the result of that:

NSString *strURL = [NSString stringWithFormat:@"http://www.imagine-app.nl/companySearch.php?companyNameSearchField=%@&companyCitySearchField=%@", companyNameSearchField.text, companyCitySearchField.text];
NSData *dataURL = [NSData dataWithContentsOfURL:[NSURL URLWithString:strURL]];
strResult = [[NSString alloc] initWithData:dataURL encoding:NSUTF8StringEncoding];
NSArray *companies = [inputString componentsSeparatedByString:@"},{"];
NSDictionary *dictionary = [NSJSONSerialization JSONObjectWithData:[NSData dataWithContentsOfFile:companies] options:kNilOptions error:nil];

To me, this makes sense. First, turn an NSString into an NSArray to separate objects, and after that convert the string into an NSDictionary, which can be used by the tableview I want to populate with this. But when I log the dictionary, it says null, so no NSDictionary seems to be made by this code.

Now after several weeks of trying and searching, i'm starting to feel pretty stupid and desperate because I cannot find a good way to do this.

Does anyone know bow to turn a json string as shown above, into an NSDictionary?

Answer 1

What you want to do is the following:

NSURL *anURL = [NSURL URLWithString:[NSString stringWithFormat:@"http://www.imagine-app.nl/companySearch.php?companyNameSearchField=%@&companyCitySearchField=%@", companyNameSearchField.text, companyCitySearchField.text]];
NSData *jsonData = [NSData dataWithContentsOfURL:anURL];
NSArray *mainArray = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:NULL];
// In mainArray are NSDictionaries
for (NSDictionary *informationOnOneCompany in mainArray) {
    NSString *name = informationOnOneCompany[@"companyName"];
    NSString *city = informationOnOneCompany[@"companyCity"];
    // Now you can store these two strings in that array or whatever populates your tableview ;)
}

Lets have a look at the steps:

1. We create an NSURL instance with the link we want.
2. We download the contents of that link into an NSData object.
3. We know how the JSON we receive looks like and identify that the "top layer" is an array. So we create an NSArray and initialize it with the JSON we received.
4. The curly braces and the colons in the JSON you posted tell us that in that array we created are instances of NSDictionary.
5. We loop through the NSArray using fast enumeration.
6. In every NSDictionary we look at the keys "companyName" and "companyCity" and store their values in an NSString.
7. Not implemented in the code above: You can populate your NSArray which is the datasource of your tableView

Hope that helps, if you have questions let me know ;)

Answer 2

No, it doesn't make sense at all, at several places. For example:

[NSData dataWithContentsOfFile:companies]

Huh, what? companies is an NSArray containing NSStrings - it's not a file path which points to a file you could initialize the data object with.

(It seems you're making assumptions about what the individual methods do - why that? It would be better to read the documentation - you wouldn't waste your and our time.)

The text/data you presented in the question is also not valid JSON. The only thing I can imagine is that the web service does indeed return valid JSON, i. e. the comma-separated dictionaries are correctly wrapped between [ ] to form an array, you just forgot to include them. In this case, you don't have to rape the string and poor Foundation framework, just convert the JSON to an array and it will be fine:

NSURL *url = [NSURL URLWithString:@"http://example.com/foo.json"];
NSData *data = [NSData dataWithContentsofURL:url];
NSArray *response = [NSJSONSerialization jsonObjectWithData:data options:kNilOptions error:NULL];