Question

i have a class RequestHandler that takes the requests for some ViewController and fetches data on the web asynchronously. In order to notify the ViewController, it implements a protocol and the ViewController is set as its delegate.

Now, this ViewController is a TableViewController, and when a row is selected, it pushes a second ViewController on the NavigationStack. This second (child) ViewController needs to use the RequestHandler too. How can i make it a delegate for the same RequestHandler instance? And how can i make sure it won’t mess with the parent TableViewController once i go back to it?

Answer 1

The fact that both view controller would want the same request suggests a design error. The view controllers should display the current state of the Model. They should not directly deal with active network requests.

You should have some group of classes that represent your data. These are called the Model. View controllers should only care about the model while the view is onscreen. So a reasonable pattern looks like this:

• ViewController registers for notifications of changes in the Model
• ViewController updates view with current data from Model.
• ViewController requests an update.
• RequestManager (singleton) creates a new RequestHandler to process it.
• When RequestHandler finishes, it tells RequestManager and is released.
• RequestManager updates Model with new data
• Model alerts registered observers that it has changed.
• ViewController updates view with current data from Model.

Now it doesn’t matter if the user is on this view, or has moved to another, or moves to another and comes back. In call cases, any time the model changes, the current view is updated.