来自JSON的字典中的键

Question

I'm importing a JSON dictionary. I need to know the name of the keys to work with it.

The dictionary is loading the data ok:

   - (void)connectionDidFinishLoading:(NSURLConnection *)connection {
[connection release];
NSString *responseString = [[NSString alloc] initWithData:responseData encoding:NSUTF8StringEncoding];
[responseData release];    
  NSDictionary *results = [responseString JSONValue];
  NSLog(@"tenga: %@",results);

but when I try to get the names of the keys the app crashes:

NSArray * keys = [results allKeys];
NSLog(@"keys: %@",keys); ...}

error message:

[__NSArrayM allKeys]: unrecognized selector sent to instance 0x5a16b30 2011-08-30 22:52:26.171 Twitter Search[1906:207] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSArrayM allKeys]: unrecognized selector sent to instance 0x5a16b30'

Why is allKeys not working?

How do I get the names for my keys so I can start working with the objects?

edit

Im using the http://code.google.com/p/json-framework Stig Brautaset json framework

Answer 1

The URL that you obtained that JSON string from gave you an array, not an object ie it looked something like:

[ { "foo1" : "bar1" }, { "foo2" : "bar2" },... ]

Note the brackets [ ] . In that situation, your JSON parser gave you an NSArray as the top level (Objective-C) object. You need some logic like:

id results = [responseString JSONValue];
if ([results isKindOfClass: [NSArray class]])
{
    // probably iterate through whtever is in it
}
else if ([results isKindOfClass: [NSDictionary class]])
{
    // dictionary at the top level.  Hooray!
}
else
{
    // something went horribly wrong, deal with it.
}

Answer 2

What you have here is the results is not an NSDictionary but rather a NSArray. NSArray doesn't have the allKeys selector causing the crash. If you'd post more info on the JSON Framework you are using, we could help source the issue better

Answer 3

发布日志说这个调用[responseString JSONValue]返回NSArray 。