Question

I’ve a method with this part of code:

NSDictionary *tmpDict = [self getJsonDictionary];

NSInteger tmpID;

for (NSDictionary *d in tmpDict) {
    tmpID = [[d objectForKey:@"id"] integerValue];
}

tmpDict is a NSDictionary with variable size. If tmpDict contains at least 2 objects (2 NSDictionary) it works well but if it contains only 1 object (1 NSDictionary) throws this exception:

 -[NSCFString objectForKey:]: unrecognized selector sent to instance 0x4e866d0
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString objectForKey:]: unrecognized selector sent to instance 0x4e866d0'

Why this? And how to fix if tmpDict has only 1 object?

Probably for (NSDictionary *d in tmpDict) is the problem and when tmpDict has 1 object d is a NSCFString, but why?

— UPDATE

The problem is when tmpDict has 1 item (one NSDictionary) the for (NSDictionary *d in tmpDict) take every key/value item in the dictionary and this is the reason for exception. Otherwise if tmpDict has 2+ items is a NSDictionary of NSDictionary and it works well. I need a way to fix this still using the for loop. Ideas?

— UPDATE 2*

Actually this code works but it’s redundant:

if ([tmpObject isKindOfClass:[NSDictionary class]]) {
    tmpID = [[tmpObject objectForKey:@"id"] integerValue];
    tmpProp2 = [tmpObject objectForKey:@"prop2"];
    tmpProp3 = [tmpObject objectForKey:@"prop3"];
    tmpProp4 = [tmpObject objectForKey:@"prop4"];
} else if ([tmpObject isKindOfClass:[NSArray class]]) {
    for (NSDictionary *d in tmpObject) {
        tmpID = [[d objectForKey:@"id"] integerValue];
        tmpProp2 = [d objectForKey:@"prop2"];
        tmpProp3 = [d objectForKey:@"prop3"];
        tmpProp4 = [d objectForKey:@"prop4"];
    }
}

It needs an improvement.

Answer 1

I’m surprised it works at all actually. For dictionaries, fast enumeration enumerates the keys. That’s why it’s telling you that -objectForKey: has been sent to an NSCFString because the key of a dictionary coming from JSON is always a string.

You should, perhaps, do this:

for (id d in [tmpDict objectEnumerator])
{
    // Objects in a JSON dictionary aren't necessarily dictionaries
    if([d isKindOfClass:[NSDictionary class]])
    {
         tmpID = [[d objectForKey:@"id"] integerValue];
    }
}

---

One possible reason why it might work with two dictionaries is if the top level item is actually an array, not a dictionary. If you have:

[ { "id" : 1 }, { "id" : 2 } ]

your JSON parser will give you an NSArray, not an NSDictionary, which can be parsed with your code even though you assume your top level item is a dictionary.

Edit: Having seen your update, I’m sure this is what is happening. If you have one object, your JSON string is looking like:

{ "id" : 1, "prop2" : "value1", "prop3" : "value1", "prop4" : "value1" }

If you have two objects, it probably looks like:

[
        { "id" : 1, "prop2" : "value1", "prop3" : "value1", "prop4" : "value1" },
        { "id" : 2, "prop2" : "value1", "prop3" : "value1", "prop4" : "value1" }
]

Notice the square brackets, that means JSON array.