iphone - Why can't I return an object from my block?

Question

I'm trying to return a NSMutableArray from my block in my method, but when I add the line return [responseString JSONValue];, I get some compiler warnings.

- (NSMutableArray*)getTodayData:(NSDate*)today
{
        ASIFormDataRequest *request = [[[ASIFormDataRequest alloc] initWithURL:url] autorelease];
        [request setPostValue:[dateFormat stringFromDate:today] forKey:@"target_date"];
        NSError *error = [request error];

        [request setCompletionBlock:^{
            NSString *responseString;
            if (!error) {
                responseString = [request responseString];
                return [responseString JSONValue];
            } else {
                NSLog(@"error: %@", error);
            }
        }];
        [request setFailedBlock:^{
            NSString *responseString;
            if (!error) {
                responseString = [request responseString];
            } else {
                NSLog(@"error: %@", error);
            }
        }];
        [request startAsynchronous];
}

Answer 1

What are you expecting returning an object to do? Presumably the completion block that you hand to ASIFormDataRequest is declared as void (^)() (or dispatch_block or some other typedef which evaluates to void (^)()). Given this, the code calling the block isn't expecting a return value. It would be like implementing a method declared - (void)foo and trying to return an object from that; it just doesn't make sense.

Edit: After re-reading your code, I expect what you're really trying to do is returning a value from -getTodayData:. However you're executing an asynchronous request. The method -getTodayData: has already returned long before your block is executed.