How TyphoonScopeObjectGraph works

Question

Let say, I have the code below

self.customObj = self.assembly.customObj() as? NSObject
let temp3 = self.assembly.customObj() as NSObject

If I use TyphoonScopeObjectGraph for customObj, it should return the same instance. But when I debug, the customObj properties are not the same as shown:

As far as I understand, customObj and temp3 should be the same instance. But as you see in the image, customObj and temp3 have the same ObjectiveC.NSObject address but all of its properties (_shortFormatter, _longFormatter) have different address. What happen? How we can get the same instance for customObj and temp3. An example is very helpful. Thanks.

You can get the project source code from here

Answer 1

In the example above if you want self.customObj and temp3 to be the same instance, then you need either TyphoonScopeSingleton or TyphoonScopeWeakSingleton.

The way TyphoonScopeObjectGraph works is that during resolution if two instances declare that they depend on another component called context, then the same shared instance of context will be returned. However these are not retained by Typhoon. So you can load a whole object graph (eg a view controller, along with dependencies) and then discard it when done, rather than use singletons, as you might otherwise. TyphoonScopeObjectGraph is also useful for having circular dependencies, such a a controller and view, that has a delegate property pointing back to the controller.

It helps to explain with an example: Let's say we have:

@interface MyViewController : UIViewController

@property(nonatomic, strong, readonly) InjectedClass(ShoppingCart) cart;
@property(nonatomic, strong) InjectedClass(MyView) view;

@end

@interface MyView : UIViewController

@property(nonatomic, strong, readonly) InjectedClass(ShoppingCart) cart;

@end

//ShoppingCart has object-graph scope
@interface ShoppingCart
@end

Now if we ask Typhoon to give us an instance of of MyViewController, then a controller will be returned where both MyViewController and MyView will have the same instance of ShoppingCart

• If TyphoonScopePrototype was used, then each would have a different instance of ShoppingCart
• If TyphoonScopeSingleton was used, then each would have the same instance of shopping cart, but there'd be no way to release the memory.

. . so you see TyphoonScopeObjectGraph loads an object graph with shared instances, but allows that whole object graph to be discarded after the use-case.