Convert JSON feed to NSDictionary

问题

Where JSON_CATEGORY_DATA_URL_STRING is my feed URL, which returns fine as:

[
    {
        \"group\":\"For Sale\",
        \"code\":\"SSSS\"
    },
    {
        \"group\":\"For Sale\",
        \"category\":\"Wanted\",
        \"code\":\"SWNT\"
    }
]

I cannot seem to get a nice NSDictionary (or NSArray) out of the following code:

+ (NSDictionary *)downloadJSON
{

NSDictionary *json_string;
NSString *dataURL = [NSString stringWithFormat:@\"%@\", JSON_CATEGORY_DATA_URL_STRING];
NSLog(@\"%@\",dataURL);
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:dataURL]];    
NSData *response = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

json_string = [[[NSString alloc] initWithData:response encoding:NSUTF8StringEncoding]autorelease];
NSDictionary *json_dict = (NSDictionary *)json_string;
NSLog(@\"json_dict\\n%@\",json_dict);
    NSLog(@\"json_string\\n%@\",json_string);

return json_string;
}

I\'ve read many posts on this, but am not getting it.

回答1:

With IOS5 you can use NSJSONSerialization for serializing the JSON.

NSDictionary *dictionary = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];

回答2:

You can't just cast a string as a dictionary and expect it to parse the JSON. You must use a JSON parsing library to take that string and convert it into a dictionary.

回答3:

I made a class that makes this task easier. It uses iOS 5's NSJSONSerialization. Clone it from github here.

回答4:

You need to use JSON parser. here is the edited code

+ (NSDictionary *)downloadJSON
{

NSDictionary *json_string;
NSString *dataURL = [NSString stringWithFormat:@"%@", JSON_CATEGORY_DATA_URL_STRING];
NSLog(@"%@",dataURL);
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:dataURL]];    
NSData *response = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

json_string = [[[NSString alloc] initWithData:response encoding:NSUTF8StringEncoding]autorelease];
//JSONValue is a function that will return the appropriate object like dictionary or array depending on your json string.
NSDictionary *json_dict = [json_string JSONValue];
NSLog(@"json_dict\n%@",json_dict);
    NSLog(@"json_string\n%@",json_string);

return json_dict;
}

this should be the code to get the NSDictionary. but you json string is an array so instead use .

+ (NSArray *)downloadJSON
{

NSDictionary *json_string;
NSString *dataURL = [NSString stringWithFormat:@"%@", JSON_CATEGORY_DATA_URL_STRING];
NSLog(@"%@",dataURL);
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:dataURL]];    
NSData *response = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

json_string = [[[NSString alloc] initWithData:response encoding:NSUTF8StringEncoding]autorelease];
NSArray *json_dict = [json_string JSONValue];
NSLog(@"json_dict\n%@",json_dict);
    NSLog(@"json_string\n%@",json_string);

return json_dict;
}

Edit: you need to use JSON.framework to call JSONValue method.
also you need to return json_dict instead of json_string as json_string is of NSString type and not NSDictionary or NSArray.
and dont autorelease it, as it is your class variable

回答5:

create method to fetchjson data.Pass your url in urlwithstring.

-(void)fetchjsondata
{
     NSString *login= [[NSString stringWithFormat:@"your url string"]stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

    NSLog(@"----%@", login);
    NSURL *url = [NSURL URLWithString:[login stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]];
    //-- Get request and response though URL
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:url];


    [NSURLConnection sendAsynchronousRequest:request
                                       queue:[NSOperationQueue mainQueue]
                           completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
                               dispatch_async(dispatch_get_main_queue(), ^{
                                   if (data) {
                                       dic_property= [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:nil];
                                       NSLog(@"%@", dic_property);
                                       NSLog(@"counts=%d",[[dic_property objectForKey:@"Data"]count]);



                                   }
                                   else {
                                       NSLog(@"network error, %@", [error localizedFailureReason]);
                                   }
                               });

                           }];

}

call fetchjsonmethod in anywhere.

[NSThread detachNewThreadSelector:@selector(fetchdata) toTarget:self withObject:nil];

来源：https://stackoverflow.com/questions/5038371/convert-json-feed-to-nsdictionary