When using Objection, implementation of custom protocol crashes with unrecognized selector - objective-c

Question

I am defining a custom protocol:
#protocol NGSAuthProvider <NSObject>
- (BOOL)isReady;
- (BOOL)isSessionValid;
- (void)login;
- (void)logout;
- (NSString *)accessToken;
- (BOOL)handleOpenURL:(NSURL *)url;
#end
I want to have different providers. So one is a Facebook provider:
#interface NGSFacebookAuthProvider : NSObject <NGSAuthProvider>
#end
#interface NGSFacebookAuthProvider () <FBSessionDelegate>
#property BOOL ready;
#property(nonatomic, retain) Facebook *facebook;
#property(nonatomic, retain) NSArray *permissions;
#end
#implementation NGSFacebookAuthProvider
//Implementation of fbLogin, fbLogout and the methods in NGSAuthProvider that forward calls to self.facebook
- (NSString *)accessToken
{
return [self.facebook accessToken];
}
#end
I setup Objection to bind from my class to the protocol.
#interface NGSObjectionModule : ObjectionModule
#end
#implementation NGSObjectionModule
- (void)configure
{
self bind:[NGSFacebookAuthProvider class] toProtocol:#protocol(NGSAuthProvider)];
}
#end
I setup the Global Injector:
#implementation NGSAppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
ObjectionModule *module = [[NGSObjectionModule alloc] init];
ObjectionInjector *injector = [Objection createInjector:module];
[module release];
[Objection setGlobalInjector:injector];
}
I am using this in my RootViewController like this:
#interface RootViewController : UITableViewController
#end
#interface RootViewController ()
#property(nonatomic, retain) id<NGSAuthProvider> authProvider;
#end
#implementation RootViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.authProvider = [[Objection globalInjector] getObject:#protocol(NGSAuthProvider)];
}
- (void)processConfig {
NSString *token = [self.authProvider accessToken];
// use the access token
}
#end
When I run this, I get the following error:
2011-07-26 21:46:10.544 ngs[6133:b603] +[NGSFacebookAuthProvider accessToken]: unrecognized selector sent to class 0x30c7c
2011-07-26 21:46:10.546 ngs[6133:b603] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+[NGSFacebookAuthProvider accessToken]: unrecognized selector sent to class 0x30c7c'
*** Call stack at first throw:
(
0 CoreFoundation 0x00e825a9 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x00fd6313 objc_exception_throw + 44
2 CoreFoundation 0x00e8417b +[NSObject(NSObject) doesNotRecognizeSelector:] + 187
3 CoreFoundation 0x00df3966 ___forwarding___ + 966
4 CoreFoundation 0x00df3522 _CF_forwarding_prep_0 + 50
5 ngs 0x0000324b -[RootViewController processConfig] + 731
6 ngs 0x000041a2 __33-[RootViewController viewDidLoad]_block_invoke_0 + 50
So my class implements the protocol. It successfully is assigned to id<NGSAuthProvider>. I tried contructing [[NGSFacebookAuthProvider alloc] init] explicitly instead of using Objection and it still crashed.
I tried looping through the selectors using objc/runtime.h methods to see which selectors are there but the only thing it finds is initialize:
- (void)logSelectors:(id)obj
{
int i=0;
unsigned int mc = 0;
Method * mlist = class_copyMethodList(object_getClass([obj class]), &mc);
NSLog(#"%d methods", mc);
for(i=0;i<mc;i++)
NSLog(#"Method no #%d: %s", i, sel_getName(method_getName(mlist[i])));
free(mlist);
}
This has to be something simple that I am missing. I use protocols defined by Cocoa and don't have this issue. I have defined custom protocols for UIViewController-based delegates without issue.
I am stumped as to why Obj-C runtime can't find my methods! If I change id<NGSAuthProvider> to NGSFacebookAuthProvider and construct it explicitly then it all works.
SOLUTION:
The problem was I misunderstood how to bind to a protocol. One way that works is:
#implementation NGSObjectionModule
- (void)configure
{
[self bind:[[[NGSFacebookAuthProvider alloc] init] autorelease] toProtocol:#protocol(NGSAuthProvider)];
}
#end
What I would like to do is bind a class to a protocol, but Objection probably wouldn't know the initializer to call?

Answer 1

The issue is you're trying to use the static class method (denoted because you've got a +) instead of a method run on an instance of your object (which is what you've written it as, with a -)

Answer 2

Chris,
You could use Objection's meta class bindings that allows you to bind a meta class to a protocol and invoke class methods against the meta class instance.
For example,
[self bindMetaClass:[NGSFacebookAuthProvider class] toProtocol:#protocol(NGSAuthProvider)];
But only if you want to use class methods. Otherwise you can use the protocol bindings against a share instance.

Answer 3

I also faced the same issue as I was using
[self bind:[MyClass class] toProtocol:#protocol(MyProtocol)];
The right way for it to work is
[self bindClass:[MyClass class] toProtocol:#protocol(MyProtocol)];