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up vote 0 down vote favorite

From a private library, I'm using a block function like this, but don't know how actually they are created. How they will returned back to my class and execute the block ?

ImAnotherClass *sameObj = [[ImAnotherClass alloc] init];

[sameObj testFunctionWithBlock:^(BOOL success, NSError *error) 
{
    if(!error)
    NSLog(@"you'll only read this, once test function was done!");
}];

[sameObj release];

Here, the notable thing is, a testfunction can take good time (in minutes) to complete its execution, but it will perfectly print the line in block ! even my function gets executed already.

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2 Answers 2

up vote 2 down vote accepted 
//your class .h
 + (void) doSomething:(NSString *) string
                   successCallback:(void (^)(id successValue)) successCallback
         errorCallback:(void (^)( NSString *errorMsg)) errorCallback;


//your class.m
+ (void) doSomething:(NSString *) string
                   successCallback:(void (^)(id successValue)) successCallback
         errorCallback:(void (^)( NSString *errorMsg)) errorCallback {

   //do your work here
   //set your bool for error

    if(error) {
        errorCallback(<error value>);
    } else {


        successCallback(<value on success>);
    }
}

make object of your calss and use you dont need sleep it will not let control pass till the block is executed

 [objYourClass  doSomething:(NSString *) string
                           successCallback:(void (^)(id successValue)) successCallback{
    //get your success value

    }
                 errorCallback:(void (^)( NSString *errorMsg)) errorCallback{
//get your error value
    }];
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This will successfully block control from moving ahead –  amar Dec 1 '12 at 8:17
    
I have passed string you can pass any thing –  amar Dec 1 '12 at 8:20
up vote 0 down vote

If you’re wondering how the function is implemented inside, it could look like this:

- (void) doSomethingWithCompletion: (dispatch_block_t) completion
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        sleep(10); // wait for ten seconds
        if (completion) {
            dispatch_async(dispatch_get_main_queue(), completion);
        }
    });
}
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