How to check if an NSDictionary or NSMutableDictionary contains a key?

Question

I need to check if an dict has a key or not. How?

Answer 1

if ( [dictionary[@"data"][@"action"] isKindOfClass:NSNull.class ] ){
   //do something if doesn't exist
}

This is for nested dictionary structure

Answer 2

Using Swift, it would be:

if myDic[KEY] != nil {
    // key exists
}

Answer 3

objectForKey will return nil if a key doesn't exist.

Answer 4

For checking existence of key in NSDictionary:

if([dictionary objectForKey:@"Replace your key here"] != nil)
    NSLog(@"Key Exists");
else
    NSLog(@"Key not Exists");

Answer 5

I like Fernandes' answer even though you ask for the obj twice.

This should also do (more or less the same as Martin's A).

id obj;

if ((obj=[dict objectForKey:@"blah"])) {
   // use obj
} else {
   // Do something else like creating the obj and add the kv pair to the dict
}

Martin's and this answer both work on iPad2 iOS 5.0.1 9A405

Answer 6

Yes. This kind of errors are very common and lead to app crash. So I use to add NSDictionary in each project as below:

//.h file code :

@interface NSDictionary (AppDictionary)

- (id)objectForKeyNotNull : (id)key;

@end

//.m file code is as below

#import "NSDictionary+WKDictionary.h"

@implementation NSDictionary (WKDictionary)

 - (id)objectForKeyNotNull:(id)key {

    id object = [self objectForKey:key];
    if (object == [NSNull null])
     return nil;

    return object;
 }

@end

In code you can use as below:

NSStrting *testString = [dict objectForKeyNotNull:@"blah"];