CODEWITHSUNDEEP
iosobjective-cif-statementrefactoring
Curt Rand
Curt Rand

Reputation: 1045

Objective C: How to check object type without a lot of if statements

I am trying to set my text string to a URL. The following code works, but I feel like I can refactor it to make it look neater. 

NSString *text = @“”;

id json = [NSJSONSerialization JSONObjectWithData:[data dataUsingEncoding:NSUTF8StringEncoding] options:0 error:nil];

if ([json isKindOfClass:[NSDictionary class]]) {

   id data = json[@“data”];

    if ([data isKindOfClass:[NSDictionary class]]) {
       id value = data[@"value"];

       if ([value isKindOfClass:[NSArray class]]) {
            id url = [value valueForKey:@"url"];

          if ([url isKindOfClass:[NSString class]]) {
             text  = url;
         }
       }
     }
   }

So far it has the whole "mountain of doom" going on and I want to know how can I check if the object type is correct without using so many if statements. Any tips or suggestions are appreciated.

Edit: This is the lite version of my code, but the concept is the same.

Upvotes: 0

Views: 69

Answers (1)

trungduc
trungduc

Reputation: 12144

In my opinion, there are 2 ways to make it look neater and ignore if-else-nesting-hell.

  • Using return.

    NSString *text = @“”;

id json = [NSJSONSerialization JSONObjectWithData:[data dataUsingEncoding:NSUTF8StringEncoding] options:0 error:nil];

if (![json isKindOfClass:[NSDictionary class]]) {
  return;
}
id data = json[@“data”];

if (![data isKindOfClass:[NSDictionary class]]) {
  return;
}
id value = data[@"value"];

if (![value isKindOfClass:[NSArray class]]) {
  return;
}
id url = [value valueForKey:@"url"];

if (![url isKindOfClass:[NSString class]]) {
  return;
}
text  = url;

  • Create a generic method which checks kind of class and return a safe value

    - (id)safeValueFromObject:(id)object forKey:(NSString *)key class:(Class)valueClass {
  if (![object respondsToSelector:@selector(valueForKey:)]) {
    return [[valueClass alloc] init];
  }

  id result = [object valueForKey:key];
  return [result isKindOfClass:valueClass] ? result : [[valueClass alloc] init];
}

    Use

    NSString *text = @"";

id json = [NSJSONSerialization JSONObjectWithData:[data dataUsingEncoding:NSUTF8StringEncoding] options:0 error:nil];
id data = [self safeValueFromObject:json forKey:@"data" class:NSDictionary.class];
id value = [self safeValueFromObject:data forKey:@"value" class:NSArray.class];
id url = [self safeValueFromObject:value forKey:@"url" class:NSString.class];
text  = url;

Upvotes: 3

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