How to check JSON Object is not empty?

Question

I'm making a small app to allow users to look up books on openlibrary.org.

The app is still quite basic but works with looking up and parsing the json data. The issue I'm having is creating a check to make sure some data is there in the first place.

On openlibrary, if the ISBN number you search with exists, you get json data: https://openlibrary.org/api/books?bibkeys=0586057242&f&jscmd=data&format=json

If however you look up an ISBN that does not exist, you simply get an empty object returned to you as so: https://openlibrary.org/api/books?bibkeys=123&f&jscmd=data&format=json

How do I implement a check to see if there is actually data there to parse? At the moment my app doesn't crash if there is nothing there, it just doesn't do anything. I'd like to setup an error popup to the user when no data is found, but can not figure out how to do that initial check.

Indeed it would, but alas it does not so I have to find a work around. — aamck
– aamck, Commented Jun 18, 2015 at 0:08

Duncan C · Accepted Answer · 2015-06-18 00:22:18Z

2

What are you expecting? A dictionary? If so, you're in luck. I believe that the empty braces you get when the query results are empty represents an empty dictionary. So just always convert your response to a data object with JSONObjectWithData, then check the count of the result. If the count is zero, your result-set is empty.

answered Jun 18, 2015 at 0:22

Duncan C

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2 Comments

aamck Over a year ago

This is exactly what I was expecting to happen but when I do it and it's supposed to fail & give me an error, nothing happens.

aamck Over a year ago

Ok, I was being a moron & placing my if statement 2 lines down in the wrong place. This is fixed & works, many thanks for the advice.

Karlo A. López · Accepted Answer · 2015-06-18 00:43:20Z

1

You only have to check if the result of the JSON parse is nil, in that case the data does not have the correct format.

 NSError *error;
    if ([NSJSONSerialization JSONObjectWithData:JSONdata options:kNilOptionserror:nil] == nil)
    {
        // Handle error
    }

SWIFT:

import Foundation

if NSJSONSerialization.JSONObjectWithData(jsonData, options: nil, error: &error) as NSDictionary == nil{

}

Or you can get a BOOL telling you if the data is correct.

[NSJSONSerialization isValidJSONObject:jsonObj];
//THis actually returns a BOOL

SWIFT:

NSJSONSerialization.isValidJSONObject(jsonObj)

Hope it helps.

edited Jun 18, 2015 at 0:43

answered Jun 17, 2015 at 23:42

Karlo A. López

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2 Comments

aamck Over a year ago

Isn't this Obj-C code though & be a pain to integrate into my Swift project?

Karlo A. López Over a year ago

There you have it in swift, I didnt see the tags

Siriss · Accepted Answer · 2015-06-18 00:31:31Z

0

Usually, you turn that response into an array. The array can contain arrays of dictionaries, or be an array of dictionaries. Here is how I handle it.

NSError *error;
NSData *URLData = [NSData dataWithContentsOfURL:<yourURL>];
NSArray *array = [NSJSONSerialization JSONObjectWithData:URLData options:NSJSONReadingMutableContainers error:&error];
if (error) {
    NSLog(@"THERE WAS AN ERROR IMPORTING JSON");
}
if ([array count] > 0)
{
    //Something here
} else {
    //NO Data
}

answered Jun 18, 2015 at 0:31

Siriss

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Comments

Yuji · Accepted Answer · 2015-06-19 02:28:19Z

0

Check if the NSData is equal to NSString "{}"

If let (yourNSDataFromURL as? NSString) == "{}" {/*do what ever you want to**/}

You can also check if the key of certain key is nil or not

answered Jun 19, 2015 at 2:28

Yuji

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