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POWhen using Objection, implementation of custom protocol crashes with unrecognized selector
 

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  1. POWhen using Objection, implementation of custom protocol crashes with unrecognized selector
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    <p>I am defining a custom protocol:</p> <pre><code>@protocol NGSAuthProvider &lt;NSObject&gt; - (BOOL)isReady; - (BOOL)isSessionValid; - (void)login; - (void)logout; - (NSString *)accessToken; - (BOOL)handleOpenURL:(NSURL *)url; @end </code></pre> <p>I want to have different providers. So one is a Facebook provider:</p> <pre><code>@interface NGSFacebookAuthProvider : NSObject &lt;NGSAuthProvider&gt; @end @interface NGSFacebookAuthProvider () &lt;FBSessionDelegate&gt; @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 </code></pre> <p>I setup <a href="https://github.com/atomicobject/objection">Objection</a> to bind from my class to the protocol.</p> <pre><code>@interface NGSObjectionModule : ObjectionModule @end @implementation NGSObjectionModule - (void)configure { self bind:[NGSFacebookAuthProvider class] toProtocol:@protocol(NGSAuthProvider)]; } @end </code></pre> <p>I setup the Global Injector:</p> <pre><code>@implementation NGSAppDelegate - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { ObjectionModule *module = [[NGSObjectionModule alloc] init]; ObjectionInjector *injector = [Objection createInjector:module]; [module release]; [Objection setGlobalInjector:injector]; } </code></pre> <p>I am using this in my RootViewController like this:</p> <pre><code>@interface RootViewController : UITableViewController @end @interface RootViewController () @property(nonatomic, retain) id&lt;NGSAuthProvider&gt; 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 </code></pre> <p>When I run this, I get the following error:</p> <pre><code>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 </code></pre> <p>So my class implements the protocol. It successfully is assigned to <code>id&lt;NGSAuthProvider&gt;</code>. I tried contructing <code>[[NGSFacebookAuthProvider alloc] init]</code> explicitly instead of using <a href="https://github.com/atomicobject/objection">Objection</a> and it still crashed.</p> <p>I tried looping through the selectors using <code>objc/runtime.h</code> methods to see which selectors are there but the only thing it finds is <code>initialize</code>:</p> <pre><code>- (void)logSelectors:(id)obj { int i=0; unsigned int mc = 0; Method * mlist = class_copyMethodList(object_getClass([obj class]), &amp;mc); NSLog(@"%d methods", mc); for(i=0;i&lt;mc;i++) NSLog(@"Method no #%d: %s", i, sel_getName(method_getName(mlist[i]))); free(mlist); } </code></pre> <p>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 <code>UIViewController</code>-based delegates without issue.</p> <p>I am stumped as to why Obj-C runtime can't find my methods! If I change <code>id&lt;NGSAuthProvider&gt;</code> to <code>NGSFacebookAuthProvider</code> and construct it explicitly then it all works.</p> <p>SOLUTION:</p> <p>The problem was I misunderstood how to bind to a protocol. One way that works is:</p> <pre><code>@implementation NGSObjectionModule - (void)configure { [self bind:[[[NGSFacebookAuthProvider alloc] init] autorelease] toProtocol:@protocol(NGSAuthProvider)]; } @end </code></pre> <p>What I would like to do is bind a class to a protocol, but Objection probably wouldn't know the initializer to call?</p>
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