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POPassing blocks to asynchronous methods
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  1. POPassing blocks to asynchronous methods
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    copied!<p>I'm passing a block to an asynchronous method which executes this block later. My app crashes if I don't copy the block before passing it to someMethod:success:failure:</p> <p>Is there a way to copy the blocks in forwardInvocation: instead of copying it before passing it to someMethod:success:failure: ?</p> <p>The flow is <strong>someMethod:success:failure: -> forwardInvocation: -> httpGet:success:failure</strong></p> <p>httpGet:success:failure: executes the success or the failure block depending on the HTTP status code.</p> <pre><code>// AppDelegate.h @interface AppDelegate : UIResponder &lt;UIApplicationDelegate&gt; @property (strong, nonatomic) id response; @property (strong, nonatomic) NSError *error; @end // AppDelegate.m @implementation AppDelegate - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { // The app crashes if the blocks are not copied here! [[MyController new] someMethod:[^(NSString *response) { self.response = response; NSLog(@"response = %@", response); } copy] failure:[^(NSError *error) { self.error = error; } copy]]; return YES; } @end // MyController.h @protocol MyControllerProtocol &lt;NSObject&gt; @optional - (void)someMethod:(void (^)(NSString *response))success failure:(void (^)(NSError *error))failure; @end @interface MyController : NSObject &lt;MyControllerProtocol&gt; @end // MyController.m #import "MyController.h" #import "HTTPClient.h" @implementation MyController - (void)forwardInvocation:(NSInvocation *)invocation { [invocation retainArguments]; NSUInteger numberOfArguments = [[invocation methodSignature] numberOfArguments]; typedef void(^SuccessBlock)(id object); typedef void(^FailureBlock)(NSError *error); __unsafe_unretained SuccessBlock successBlock1; __unsafe_unretained SuccessBlock failureBlock1; [invocation getArgument:&amp;successBlock1 atIndex:(numberOfArguments - 2)]; // success block is always the second to last argument (penultimate) SuccessBlock successBlock = [successBlock1 copy]; [invocation getArgument:&amp;failureBlock1 atIndex:(numberOfArguments - 1)]; // failure block is always the last argument FailureBlock failureBlock = [failureBlock1 copy]; NSLog(@"successBlock copy = %@", successBlock); NSLog(@"failureBlock copy = %@", failureBlock); // Simulates a HTTP request and calls the success block later! [HTTPClient httpGet:@"somerequest" success:successBlock failure:failureBlock]; } - (NSMethodSignature *)methodSignatureForSelector:(SEL)sel { NSMethodSignature *methodSignature = [super methodSignatureForSelector:sel]; return methodSignature; } @end // HTTPClient.h @interface HTTPClient : NSObject + (void)httpGet:(NSString *)path success:(void (^)(id object))success failure:(void (^)(NSError *error))failure; @end // HTTPClient.m #import "HTTPClient.h" @implementation HTTPClient + (void)httpGet:(NSString *)path success:(void (^)(id object))success failure:(void (^)(NSError *error))failure { // Invoke the method. double delayInSeconds = 2.0; dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC)); dispatch_after(popTime, dispatch_get_main_queue(), ^{ success(@"foo"); }); } @end </code></pre> <p>The complete source code can be found here: <a href="https://github.com/priteshshah1983/BlocksWithNSInvocation" rel="nofollow">https://github.com/priteshshah1983/BlocksWithNSInvocation</a></p> <p>Can you please help?</p>
 

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