List selectors for Objective-C object

Question

I have an object, and I want to list all the selectors to which it responds. It feels like this should be perfectly possible, but I'm having trouble finding the APIs.

Answer 1

This is a solution based on the runtime C functions:

class_copyMethodList returns a list of class methods given a Class object obtainable from an object.

#import <objc/runtime.h>

[..]

SomeClass * t = [[SomeClass alloc] init];

int i=0;
unsigned int mc = 0;
Method * mlist = class_copyMethodList(object_getClass(t), &mc);
NSLog(@"%d methods", mc);
for(i=0;i<mc;i++)
    NSLog(@"Method no #%d: %s", i, sel_getName(method_getName(mlist[i])));

/* note mlist needs to be freed */

Answer 2

I think usually you'll want to do that in the console, instead of cluttering your code with debug code. This is how you can do that while debugging in lldb:

(Assuming an object t)

p int $num = 0;
expr Method *$m = (Method *)class_copyMethodList((Class)object_getClass(t), &$num);
expr for(int i=0;i<$num;i++) { (void)NSLog(@"%s",(char *)sel_getName((SEL)method_getName($m[i]))); }

Answer 3

This is also possible with Swift:

let obj = NSObject()

var mc: UInt32 = 0
let mcPointer = withUnsafeMutablePointer(&mc, { $0 })
let mlist = class_copyMethodList(object_getClass(obj), mcPointer)

print("\(mc) methods")

for i in 0...Int(mc) {
    print(String(format: "Method #%d: %s", arguments: [i, sel_getName(method_getName(mlist[i]))]))
}

Output:

251 methods
Method #0: hashValue
Method #1: postNotificationWithDescription:
Method #2: okToNotifyFromThisThread
Method #3: fromNotifySafeThreadPerformSelector:withObject:
Method #4: allowSafePerformSelector
Method #5: disallowSafePerformSelector
...
Method #247: isProxy
Method #248: isMemberOfClass:
Method #249: superclass
Method #250: isFault
Method #251: <null selector>

Tested with the 6s simulator running iOS 9.2, Xcode Version 7.2 (7C68).

Answer 4

Something like this should work (just put it in the object you're curious about). For example if you have an object that's a delegate and want to know what 'hooks' are available this will print out messages to give you that clue:

-(BOOL) respondsToSelector:(SEL)aSelector {
    printf("Selector: %s\n", [NSStringFromSelector(aSelector) UTF8String]);
    return [super respondsToSelector:aSelector];
}

Note that I discovered this in the iPhone Developer's Cookbook so I can't take credit! For example output I get from a UIViewController that implements the protocols <UITableViewDelegate, UITableViewDataSource>:

Selector: tableView:numberOfRowsInSection:
Selector: tableView:cellForRowAtIndexPath:
Selector: numberOfSectionsInTableView:
Selector: tableView:titleForHeaderInSection:
Selector: tableView:titleForFooterInSection:
Selector: tableView:commitEditingStyle:forRowAtIndexPath:
Selector: sectionIndexTitlesForTableView:
Selector: tableView:sectionForSectionIndexTitle:atIndex:
...
...
etc.,etc.

Answer 5

Taking inspiration from JAL's answer, in Swift you can do:

extension NSObject {
    var __methods: [Selector] {
        var methodCount: UInt32 = 0
        guard
            let methodList = class_copyMethodList(type(of: self), &methodCount),
            methodCount != 0
        else { return [] }
        return (0 ..< Int(methodCount))
            .flatMap({ method_getName(methodList[$0]) })
    }
}

Answer 6

ARC realization

SomeClass *someClass = [[SomeClass alloc] init];    

//List of all methods
unsigned int amountMethod = 0;
Method *methods = class_copyMethodList(someClass, &amountMethod);

for (unsigned int i = 0; i < amountMethod; i++) {
    Method method = methods[i];

    printf("\t method named:'%s' \n", sel_getName(method_getName(method)));
}

free(methods);