CODEWITHSUNDEEP
iphoneobjective-casynchronousgrand-central-dispatchnsoperation
tacos_tacos_tacos
tacos_tacos_tacos

Reputation: 10585

In Objective-C, return something that has to wait before its done

Consider following code involving SpecialRequest, which has member result that is not populated right away:

- (NSArray *)getXboxSizedArray {
   SpecialRequest *request = [SpecialRequest request];
   request.someParam = 11; //and so forth...
   [request start];
}

And say there is a callback for requestFinished:

- (void)requestFinished:(SpecialRequest *)request {
   //hooray!
}

I want to return the value of request.result, but of course only after the request has completed (which I would know from -(void)requestFinished. How do I do this?

Edit: Note that I have tried putting a return statement inside a block, and failed miserably.

Edit 1: Here is an example of bad and non working code if you are interested:

- (NSString *)getAllDogFoodBrand {
    __unsafe_unretained __block ASIHTTPRequest *request = [[ASIHTTPRequest alloc] initWithURL:[NSURL URLWithString:@"some_url"]];
    request.delegate = self;
    [request setCompletionBlock:^{
        [self.delegate objectControllerDidFinishRequestWithStatus:request.responseStatusMessage];
        //return request.responseString; <-- this line makes compiler :(
    }];
    [request startAsynchronous];
}

Upvotes: 1

Views: 278

Answers (2)

Wolfgang Schreurs
Wolfgang Schreurs

Reputation: 11834

Another approach could be to create a wrapper class for your request with a method that accepts a block parameter. The block parameter could be stored in an instance variable (generally a copy property) and after the request has finished the completion block stored in the instance variable can be called from the -requestFinished: callback method. This is in my opinion a neater approach compared to using delegates.

Upvotes: 1

Nekto
Nekto

Reputation: 17877

You can use for that purposes combination of delegate and protocol. For example, here you could find a small tutorial: The Basics of Protocols and Delegates

Also you could use KVC with KVO. Check here about that approaches here: Key-Value Observing Programming Guide

Upvotes: 0

Related Questions