Synchronous calling web API service for a generic method - restkit

Question

I am using RestKit version 0.20.3 to make a generic method that is used in many other places. The problem is the returned value from that method is always nil because the "return location;" statement is executed BEFORE the Success call back function over the [objectManager getObjectsAtPath ...] method (see below codes).
I want the "return location;" statement must WAIT for the block variable "location" is filled with data from the Success call back function inside the [objectManager getObjectsAtPath ...] method. How can I do this?
Thank you for your help.
My generic method looks like:
-(KNSunGoogleLatitudeLongitudeGeometryLocation*)getSynchronouslyLatitudeLongitudeWithAddress:(NSString*)address
{
__block KNSunGoogleLatitudeLongitudeGeometryLocation* location = [[KNSunGoogleLatitudeLongitudeGeometryLocation alloc] init];
NSURL *baseURL = [NSURL URLWithString:#"http://maps.googleapis.com/maps/api"];
AFHTTPClient * client = [AFHTTPClient clientWithBaseURL:baseURL];
[client setDefaultHeader:#"Accept" value:RKMIMETypeJSON];
RKObjectManager *objectManager = [[RKObjectManager alloc] initWithHTTPClient:client];
//1. KNSunGoogleLatitudeLongitudeGeometryLocation
RKObjectMapping *locationMapping = [RKObjectMapping mappingForClass:[KNSunGoogleLatitudeLongitudeGeometryLocation class]];
[locationMapping addAttributeMappingsFromArray:#[#"lat", #"lng"]];
//2. KNSunGoogleLatitudeLongitudeGeometry
RKObjectMapping *geometryMapping = [RKObjectMapping mappingForClass:[KNSunGoogleLatitudeLongitudeGeometry class]];
//3. KNSunGoogleLatitudeLongitude
RKObjectMapping *latLongMapping = [RKObjectMapping mappingForClass:[KNSunGoogleLatitudeLongitude class]];
//4. property/relationship mapping
[geometryMapping addPropertyMapping:[RKRelationshipMapping
relationshipMappingFromKeyPath:#"location"
toKeyPath:#"location"
withMapping:locationMapping]];
[latLongMapping addPropertyMapping:[RKRelationshipMapping
relationshipMappingFromKeyPath:#"geometry"
toKeyPath:#"geometry"
withMapping:geometryMapping]];
// 6. response
RKResponseDescriptor * responseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:latLongMapping
method:RKRequestMethodGET
pathPattern:nil
keyPath:#"results"
statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
// 7
[objectManager addResponseDescriptor:responseDescriptor];
NSDictionary *queryParams;
queryParams = [NSDictionary dictionaryWithObjectsAndKeys:address, #"address", #"false", #"sensor", nil];
// 6
[objectManager getObjectsAtPath:#"http://maps.googleapis.com/maps/api/geocode/json"
parameters:queryParams
success:^(RKObjectRequestOperation * operaton, RKMappingResult *mappingResult)
{
//-----------
NSArray* results = [mappingResult array];
KNSunGoogleLatitudeLongitude* result0 = [results objectAtIndex:0];
KNSunGoogleLatitudeLongitudeGeometry* geometry = result0.geometry;
location= geometry.location;
NSLog(#"lat=%#, long=%#", location.lat, location.lng);
}
failure:^(RKObjectRequestOperation * operaton, NSError * error)
{
NSLog (#"failure: operation: %# \n\nerror: %#", operaton, error);
}];
return location; // note: ALWAYS RETURNs nil
}

Answer 1

You need to change what you want because it's a bad design. You should not block the requestor while the request is in progress. Instead you should pass a block to your general method that is executed from the block you pass to RestKit. This allows you to properly respect the asynchronous nature of the request.
If you did want to proceed with blocking, you could use look at using a semaphore. But, you would need to manage this yourself. And you wouldn't be able to trigger the request on the main thread - ever. These are significant hurdles to general usage and will probably cause you issues in the future.