How to check NSDictionary for key using Objective-C literals
nsdictionary, objective-c
Solution
The new literal syntax makes no difference here. The `dict[@"public"]` code is translated into `[dict objectForKeyedSubscript:@"public"]`, which is documented to be the same as `valueForKey:`, which in turn calls `objectForKey:`.
As for the conditional test, writing `if ([dict objectForKey:@"foo"])` is the same as `if ([dict objectForKey:@"foo"] != nil)`. In other words, `[NSNull null]` counts as true here, so you have to check explicitly if you want a different behaviour. Zero can’t be directly stored in a dictionary, it would have to be wrapped in an `NSNumber`, again being treated as a true value.
See also the Objective-C Literals spec and NSDictionary Class Reference.
Problem
When parsing JSON, I get NSDictionary and go through it one (known) key at a time. When debugging a bug, I started wondering: how should I handle missing key vs value which is zero? Earlier I would have used something like this to check if key exists or not: ``` if ([dict objectForKey:@"public"]) newItem.isPublic = [dict objectForKey:@"public"] ? YES : NO; ``` but now I wrote this using Objective-C object literals. Just started wondering, what does this check actually do: ``` if (dict[@"public"]) newItem.isPublic = dict[@"public"] ? @YES : @NO; ``` Should I check against nil or [NSNull null] or is there some easier, obvious, way?