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 ([MyDictionary objectForKey:MyKey]) {
      // "Key Exist"
} 

Answer 2

if ([mydict objectForKey:@"mykey"]) {
    // key exists.
}
else
{
    // ...
}

Answer 3

When using JSON dictionaries:

#define isNull(value) value == nil || [value isKindOfClass:[NSNull class]]

if( isNull( dict[@"my_key"] ) )
{
    // do stuff
}

Answer 4

if ([[dictionary allKeys] containsObject:key]) {
    // contains key
}

or

if ([dictionary objectForKey:key]) {
    // contains object
}

Answer 5

Because nil cannot be stored in Foundation data structures NSNull is sometimes to represent a nil. Because NSNull is a singleton object you can check to see if NSNull is the value stored in dictionary by using direct pointer comparison:

if ((NSNull *)[user objectForKey:@"myKey"] == [NSNull null]) { }

Answer 6

I'd suggest you store the result of the lookup in a temp variable, test if the temp variable is nil and then use it. That way you don't look the same object up twice:

id obj = [dict objectForKey:@"blah"];

if (obj) {
   // use obj
} else {
   // Do something else
}