How can i fetch value from Json response in Objective -C

Question

I have a problem with fetching data from Json response.

Here is an example data structure :

(
     {
        AT = \"\";
        DId = 0;
            


        

Answer 1

You can use KVC to access the nested properties in the JSON. You need to know about KVC and dot syntax and Collection operators

Frameworks that map JSON to objects, such as RestKit rely heavily on KVC.

Following your sample, you could get a list of all PdCatList objects:

//sample data
NSArray *json = @[
                  @{@"PLId" : @33997,
                    @"PdCatList" : @{@"PLId": @33998,
                                     @"PPCId" : @1,
                                    @"pdList" : @{
                                      @"PCId" : @119777
                                      }}
                        },
                  @{@"PLId" : @33999,
                    @"PdCatList" : @{@"PLId": @4444,
                                     @"PPCId" : @0,
                                     @"pdList" : @{
                                             @"PCId" : @7777
                                             }}}
                    ];

//KVC
NSArray *pdCatLists = [json valueForKeyPath:@"@unionOfObjects.PdCatList"];

With this you can, for example, make a very basic object mapping (which does not take care of relationships)

In PdCatList.h

@interface PdCatList : NSObject
@property (readonly, strong, nonatomic) NSNumber *PLId;
@property (readonly, strong, nonatomic) NSNumber *PPCId;
+ (instancetype)listWithDictionary:(NSDictionary *)aDictionary;
@end

In PdCatList.m

@implementation PdCatList
- (void)setValue:(id)value forUndefinedKey:(NSString *)key
{
    @try {
        [super setValue:value forUndefinedKey:key];
    }
    @catch (NSException *exception) {
        NSLog(@"error setting undefined key: %@, exception: %@", key, exception);
    };
}
+ (id)listWithDictionary:(NSDictionary *)aDictionary
{
    PdCatList *result = [[self alloc] init];
    [result setValuesForKeysWithDictionary:aDictionary];
    return result;
}
@end

After getting the json object

NSArray *pdCatLists = [json valueForKeyPath:@"@unionOfObjects.PdCatList"];

[pdCatLists enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    PdCatList *each = [PdCatList listWithDictionary:obj];
}];

However, If what you want is just to flatten the json, you must use recursion and create a category similar to the following.

In NSJSONSerialization+FlattenedJSON.h

@interface NSJSONSerialization (FlattenedJSON)
+ (void)FlattenedJSONObjectWithData:(NSData *)data completionSuccessBlock:(void(^)(id aJson))onSuccess failure:(void(^)(NSError *anError))onFailure;
@end

In NSJSONSerialization+FlattenedJSON.m

#import "NSJSONSerialization+FlattenedJSON.h"

@implementation NSJSONSerialization (FlattenedJSON)
+ (void)FlattenedJSONObjectWithData:(NSData *)data completionSuccessBlock:(void (^)(id))onSuccess failure:(void (^)(NSError *))onFailure
{
    NSError *error;
    id object = [self JSONObjectWithData:data
                     options:kNilOptions
                       error:&error];
    if (error)
    {
        onFailure(error);
    }
    else
    {
        NSMutableArray *result = [NSMutableArray array];
        [self flatten:object
              inArray:result];
        onSuccess([result copy]);
    }
}
+ (void)flatten:(id)anObject inArray:(NSMutableArray *)anArray
{
    if ([anObject isKindOfClass:NSDictionary.class])
    {
        [((NSDictionary *)anObject) enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
            [self flatten:obj inArray:anArray];
        }];
    }
    else if ([anObject isKindOfClass:NSArray.class])
    {
        [((NSArray *)anObject) enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
            [self flatten:obj inArray:anArray];
        }];
    }
    else
    {
        [anArray addObject:anObject];
    }
}
@end