Objective-C Runtime: best way to check if class conforms to protocol?

Question

I have a Class (but no instance) and need to know if it conforms to a certain protocol. However, Class can be subclassed several times and class_conformsToProtocol() ignores protocols declared on superclasses.

I could just use class_getSuperclass() and recursively check all the classes in the hierarchy upwards until the superclass is nil. However I wonder if that might be inefficient for deeply nested class hierarchies, and maybe there's a nicer way to do that?

In other words, how is the NSObject method conformsToProtocol best implemented using Objective-C runtime methods so that it finds protocols on superclasses?

 [myObject conformsToProtocol:@protocol(MyProtocol)];

If I'm on the right track with recursively going up the class hierarchy just let me know.

Ginger

Answer 1

According to the docs,

[MyClass conformsToProtocol:@protocol(MyProtocol)];

should work.

Pirri

You're right. It was late and no code completion suggestions were made by Xcode. I checked the definition of Class and seeing that it was "typedef struct objc_class *Class" I didn't check the NSObject class reference. – Ginger

Is there any way to do it on an instance instead of a class? My self.delegate implements multiple protocols and I want to check if it conforms to others than it's class. – Metrology

@KonradPiascik Just call it on the instance instead: [someObject conformsToProtocol:@protocol(MyProtocol)]. – Pirri

Answer 2

Or, in case it is a general pointer, like:

Class<MyProtocol> someClassPointer = nil;

you can use:

[someClassPointer.class conformsToProtocol:@protocol(MyProtocol)];

Snodgrass

Answer 3

check if class conforms to protocol?

Two Method

use conformsToProtocol

• syntax
  • [someClassObj conformsToProtocol: objc_getProtocol("YourProtocolName")]
• example

(lldb) po self
<AKAnisetteProvisioningService: 0x105f16870>

(lldb) po Protocol * $akaisdProto = objc_getProtocol("AKAppleIDSigningDaemonProtocol")
(lldb) po $akaisdProto
<Protocol: 0x1dc7d2e90>

(lldb) po [self conformsToProtocol: $akaisdProto]
0x0000000000000001

use class_conformsToProtocol

• syntax
  • class_conformsToProtocol(NSClassFromString(@"YourClassName"), objc_getProtocol("YourProtocolName"))
• example

(lldb) po Class $akapsClass = NSClassFromString(@"AKAnisetteProvisioningService")
(lldb) po $akapsClass
AKAnisetteProvisioningService

(lldb) po Protocol * $akaisdProto = objc_getProtocol("AKAppleIDSigningDaemonProtocol")
(lldb) po $akaisdProto
<Protocol: 0x1dc7d2e90>

(lldb) po class_conformsToProtocol($akapsClass, $akaisdProto)
0x0000000000000001

Banker