Passing data/confirmation between views

[Yko]

Hey guys,

What is the "right" way (from a good software architect point of view) to pass data between view controllers. Here is an example:

I have a UINavigationBar with HomeViewController as the root. From the HomeViewController, it can lead to two other view controllers CartViewController and AddItemViewController. The user has to do some stuff in the AddItemViewController (get product info, confirmation, etc...) and then *data* is passed and displayed to the CartViewController to be displayed in CartView.

My question is, should the AddItemViewController pass the data directly to CartViewController or should be pass the data back to the root view controller (ie: let the root view controller handle/manage all the data) and then pass it to the other view controllers.

I hope my question makes some sense.

Thanks!

[tychop]

You could use CoreData.
Or you could add some sort of service singleton object in the appdelegate and put DTO's in there. From a VC you van easily get to the appdelegate

[Yko]

Originally Posted by tychop

You could use CoreData.
Or you could add some sort of service singleton object in the appdelegate and put DTO's in there. From a VC you van easily get to the appdelegate

Sorry for the newbness. I can read up on CoreData and have used singleton before but what is DTO and VC?

Thanks.

[Jompe71]

Originally Posted by Yko

Sorry for the newbness. I can read up on CoreData and have used singleton before but what is DTO and VC?

Thanks.

DTO, Data Transfer Object.

I've had similar thoughts as you have and came to the conclusion in my apps to do like a reversed MVC.
By this I mean that I use a singleton to handle all data loading and "storage", pretty much like tychop states.

So every time a view needs data it queries the singleton for it and that singleton is responsible for loading missing data or supplying data (like from a shoppingcart) whenever requested.
So this patterns is opposite from "broadcasting" data to N views where you in your controller do not know which view will need what data.

A metaphor would be like in a web application you load data from the backend to fulfill the need of page <alphabet>.jsp when the browser only requests a.jsp.

Bottom line is that if a view adds data to the storage/singleton class like the user adds more items the the shopping cart you do not pass that data to the check out view. The check out view asks for the data from the same singleton class when it is shown.

Hope I explain my thoughts well enough...

[Yko]

Originally Posted by Jompe71

DTO, Data Transfer Object.

I've had similar thoughts as you have and came to the conclusion in my apps to do like a reversed MVC.
By this I mean that I use a singleton to handle all data loading and "storage", pretty much like tychop states.

So every time a view needs data it queries the singleton for it and that singleton is responsible for loading missing data or supplying data (like from a shoppingcart) whenever requested.
So this patterns is opposite from "broadcasting" data to N views where you in your controller do not know which view will need what data.

A metaphor would be like in a web application you load data from the backend to fulfill the need of page <alphabet>.jsp when the browser only requests a.jsp.

Bottom line is that if a view adds data to the storage/singleton class like the user adds more items the the shopping cart you do not pass that data to the check out view. The check out view asks for the data from the same singleton class when it is shown.

Hope I explain my thoughts well enough...

Your explanation is very well. Thank you very much and I guess that is what the MVC model is all about. At first, I read in a book that usually the root view controller handles all the data and passes data to the view controllers that needed it but I may have misinterpret that. Now, I think the root view controller is responsible for handling all the controllers and there is a data model which as you mentioned is the singleton class. Then, the root view controller's responsibility is to mainly refer that data model to the different view controllers and each view controller interacts directly to the data model.

It might not be a perfect view at the moment but I think it is better than what I had before. Thanks again

Yko

[Yko]

My other question from this discussion is that I though Singleton is bad. When I first try to pass data between different views, I was told to google singleton and I did but was told that it broke the MVC when you let everything be global...

[tychop]

Originally Posted by Yko

My other question from this discussion is that I though Singleton is bad. When I first try to pass data between different views, I was told to google singleton and I did but was told that it broke the MVC when you let everything be global...

I think it's not always bad practice. I use it to create a service class which act like a broker to my data. The service & VC (View Controller) should not know how to r/w data. That's the job of the persistence layer which I call from my service class. The persistence layer then can be swapped out easily if you decide to use a different kind of storage. (Separation of concerns).
Since I only need 1 service object, I think a singleton is just fine.