Stack-based navigation: keep track of mutations in a child path in all the parents

[appfrosch]

I am playing around with stack-based navigation. I have a sample project where I have the following structure:

What I have

erDiagram
	RootView ||--|| ItemView : "shows selected item of item's list"
	ItemView ||--|| SubItemView : "shows selected **sub**item of item's **subitem's** list"

Loading

The RootView shows a list of items. I drill down to the detail view of an item with a NavigationLink.

The itemView has a title TextField and a list of subitems. Tapping on one of the subitems further drills down in the navigation stack to the detail view of this subitem.

The SubItemView also has a title TextField.

What I want to accomplish

When drilling down to an item and a subitem, I obviously want changes in the item and/or subitem to get registered by its parent and potentially grand-parent, so that when I pop to root and then drill back down, my mutations are retained.

What I am struggling with

I have it working right now, but I guess there must be a much more elegant way … Right now, when a mutation is done in one of the children, I fire up a .delegate(.onChange) action that is observed by root.

In root, I then loop over the path to try and see whether the item or subitem with that ID is part of the stack element and assign the new value.

That means that from the SubItemView, when I fire .delegate(.onChange), I have to loop over all items in root first, trying to find the one item with this exact SubItem that was changed, then assign the mutated SubItem to its parent Item. This ensures that the change is reflected in ItemView. After that, I will need to also mutate the array of Items in the ItemView.

Here's the code where I do exactly that:

case let .path(.element(id: _, action: .detailSubItem(.delegate(.onChange(subItem))))):
  //Save in root view
  state.items.ids.forEach { itemId in
    state.items[id: itemId]?.subItems.ids.forEach { subitemId in
      state.items[id: itemId]?.subItems[id: subitemId] = subItem
    }
  }
  //Save in item detail view (i.e. in each path with the subitems parent item
  state
    .path
    .ids
    .forEach { pathId in
      state.path[id: pathId, case: /Path.State.detailItem]?.item.subItems.ids.forEach { subItemId in
        if state.path[id: pathId, case: /Path.State.detailItem]?.item.subItems[id: subItemId]?.id == subItem.id {
          state.path[id: pathId, case: /Path.State.detailItem]?.item.subItems[id: subItemId] = subItem
        }
      }
    }
  return .none

This feels to be more complicated than it should be, so I am wondering whether I am "holding it wrong" TM Apple …

So I wonder …

… whether there is a better approach for doing what I want to do …

You can find the whole code as a gist here.

I am looking forward to your suggestions, thanks for considering helping me out here … :-)

[appfrosch]

I guess I will have to use StackElementID in some form or capacity.

I can see how this will work for the direct parent of the SubItemView:

state.path[id: subItemStackId, case: /Path.State.detailSubItem]?.subItem = subItem

But I cannot do something like this to mutate the RootView as well …

if let index = state.path[id: subItemStackId - 1, case: /Path.State.detailItem]?.item.subItems.firstIndex(where: { $0.id == subItem.id}) {
            state.path[id: subItemStackId - 1, case: /Path.State.detailItem]?.item.subItems[index] = subItem
          }

… cause it result in an error:

Binary operator '-' cannot be applied to operands of type 'StackElementID' and 'Int'

I think I am close, but how can I get access to the previous StackElementID?