将NSDictionary值（id？）转换为NSString或NSNumber以进行比较

Question

pls help me with my trouble: I can't compare to value to know successful result was or not. I fetch json-object as NSDictionaty:

    NSDictionary *returnDictionary = [NSJSONSerialization JSONObjectWithData:responseObject                                                                                                                                       options:0 error:nil];

And after that I get value for key: code

    [returnDictionary objectForKey:@"code"];

If returning value is equal 1 so that's OK, but problem is that I don't know the type value of key "code". I tried to compare id, NSString, NSNumber but all were fail. What type of object should I compare ?

Answer 1

Did you use the comparison operator ( == ) to compare your objects?

If so, you didn't compare the values of your objects but their memory addresses.
If the object returned by [returnDictionary objectForKey:@"code"] is of type NSString you should use NSString's isEqualToString: If it returns a NSNumber instance, you could compare the intValue of that object to 1.

[[returnDictionary objectForKey:@"code"] isEqualToString:@"1"]  

or

[[returnDictionary objectForKey:@"code"] intValue] == 1

Answer 2

You can use

[[returnDictionary objectForKey:@"code"] isKindOfClass:[NSString class]]

to check the class of the object pulled from the dictionary.

Hope it helps!

Answer 3

If you expect the output to be an integer, you can call intValue .

[[returnDictionary objectForKey:@"code"] intValue] == 1

Also, you can log the type of the returned object by + class; method.

NSLog(@"%@", [[returnDictionary objectForKey:@"code"] class]);

Answer 4

put in a breakpoint and print out the classname...

type into the debugger: po [[returnDictionary objectForKey:@"code"]className]

that will give you the class, something like _NSCFString will be a string etc...

Answer 5

id is something of a "cheat" in Objective-C, though one that is officially "blessed". Generally, where a method returns id you can directly use that value to invoke a method on the returned type, without having to first cast to the appropriate type -- the compiler knows to suppress "can't find that method name" type warnings/errors when the call is on an id .

Of course, if you don't know the class of the object, you don't know whose methods to call. As Pablo suggests you can use isKindOfClass to test, if you have a suspicion. Alternatively, you can log the class name of an object with NSLog(@"The class is %s", object_getClassName(someId)); or one or two other ways.