Passing Objects using Segue - objective-c

Question

I have trouble understanding segues and how they work and pass objects. Basically I have a calculator and am trying to graph the objects stored in an array. So far I have an object called brain which is an instance of CalculatorBrain. Now brain has an NSArray property that I use as a stack to store variables. Let's say I add the values 3 and 5 to the array and then want to segue. I have my segue selected to a button called "Graph" so when I click the button it segues. How would I pass brain to the new view controller that I am segueing to? I have a property called setGraphingPoint which is defined in the new view controller which I think should accept the passed object. Also, if I pass brain through a segue will the values 3 and 5 be passed along with it or will it create a new object of CalculatorBrain? Here is what I have so far.
This is defined in the new view controller
#property (nonatomic, strong) CalculatorBrain *graphingPoint;
#synthesize graphingPoint = _graphingPoint;
-(void) setGraphingPoint:(CalculatorBrain*) graphingPoint{
_graphingPoint = graphingPoint;
[self.graphingView setNeedsDisplay];
}
This is called from the old view controller which will have button to segue
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if([segue.identifier isEqualToString:#"Graph"])
[segue.destinationViewController setGraphingPoint:[self.brain program]];

Answer 1

You can use protocols. For instance, you can have your prepareForSegue look like this:
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
id destination = segue.destinationViewController;
if([destination conformsToProtocol:#protocol(GraphPointUsing)])
[destination setGraphingPoint:[self.brain program]];
}
Then you just have to make sure the the ViewController that you are segueing to conformist to GraphPointUsing.
If you do not want to use protocols, but you still want to call methods on GraphPoint you can do this:
//In new ViewController suppose we want to call the method `foo` on `GraphPoint`
[self.graphingPoint foo];
//Or if we want to call a setter we can do
[self.graphingPoint setFoo:5];