Felipe Sabino Felipe Sabino - 2 months ago 7
Objective-C Question

Check if object is Class type

I have a method that receives a

NSArray
of
Class
objects and I need to check if they all are
Class
type generated with the code bellow:

NSMutableArray *arr = [[NSMutableArray alloc] init];

[arr addObject:[NSObject class]];
[arr addObject:[NSValue class]];
[arr addObject:[NSNumber class]];
[arr addObject:[NSPredicate class]];
[arr addObject:@"not a class object"];


The problem is that
Class
is not an objective-c class, it is a struc, so I can not use just

for (int i; i<[arr count]; i++) {
Class obj = [arr objectAtIndex:i];

if([obj isKindOfClass: [Class class]]) {
//do sth
}
}


So, I need to I check if the
obj
variable is a
Class
type, I suppose it will be in
C
directly, but how can I do that?

It will be a plus if the answer also provide a way to check if the item in the array is a
NSObject
, as the items in the example code, the
NSPredicate
would also be
true
for the
NSObject
check

Joe Joe
Answer

To determine if an "object" is a class or an instance you need to check if it is a meta class in a two stage process. First call object_getClass then check if it is a meta class using class_isMetaClass. You will need to #import <objc/runtime.h>.

NSObject *object = [[NSObject alloc] init];
Class class = [NSObject class];

BOOL yup = class_isMetaClass(object_getClass(class));
BOOL nope = class_isMetaClass(object_getClass(object));

Both Class and *id have the same struct layout (Class isa), therefore can pose as objects and can both receive messages making it hard to determine which is which. This seems to be the only way I was able to get consistent results.

EDIT:

Here is your original example with the check:

NSMutableArray *arr = [[NSMutableArray alloc] init];

[arr addObject:[NSObject class]];
[arr addObject:[NSValue class]];
[arr addObject:[NSNumber class]];
[arr addObject:[NSPredicate class]];
[arr addObject:@"not a class object"];

for (int i; i<[arr count]; i++) {
    id obj = [arr objectAtIndex:i];

    if(class_isMetaClass(object_getClass(obj)))
    {
        //do sth
        NSLog(@"Class: %@", obj);
    }
    else
    {
        NSLog(@"Instance: %@", obj);
    }
}

[arr release];

And the output:

Class: NSObject
Class: NSValue
Class: NSNumber
Class: NSPredicate
Instance: not a class object

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