How to handle backstack referencing deleted items

Question

I'm trying to figure out how to properly handle navigating back through a fragment back stack that might point to deleted items. I would guess this is a pretty common case, but I have not found a solution for it.

    |-----------------------|--------------------------------------------------|--------------------|
    |         Action        |                    Back stack                    |      Location      |
    |-----------------------|--------------------------------------------------|--------------------|
    | View list             |                                                  | List               |
    | Go to Details(A)      | List                                             | Details(A)         |
    | Go up                 | List -> Details(A)                               | List               |
    | Go to Details(B)      | List -> Details(A) -> List                       | Details(B)         |
    | Go up                 | List -> Details(A) -> List -> Details(B)         | List               |
    | Go to Details(A)      | List -> Details(A) -> List -> Details(B) -> List | Details(A)         |
    | Delete A (pops stack) | List -> Details(A) -> List -> Details(B)         | List               |
    | Go back               | List -> Details(A) -> List                       | Details(B)         |
    | Go back               | List -> Details(A)                               | List               |
    | Go back               | List                                             | Details(A) PROBLEM |
    |-----------------------|--------------------------------------------------|--------------------|

The same problem of course occurs without involving item B, it's just to point out that the problematic item might be a bit up the stack:

    |-----------------------|----------------------------|--------------------|
    |         Action        |         Back stack         |      Location      |
    |-----------------------|----------------------------|--------------------|
    | View list             |                            | List               |
    | Go to Details(A)      | List                       | Details(A)         |
    | Go up                 | List -> Details(A)         | List               |
    | Go to Details(A)      | List -> Details(A) -> List | Details(A)         |
    | Delete A (pops stack) | List -> Details(A)         | List               |
    | Go back               | List                       | Details(A) PROBLEM |
    |-----------------------|----------------------------|--------------------|

It would make sense to remove references to deleted items from the back stack when deleting the item, but as far as I understand that's not really how the back stack works.

One workaround that seems to work is to pop the stack when creating the fragment for the missing item, but it would be nicer to not try to create the fragment for the missing item in the first place:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup viewGroup,
        Bundle savedInstanceState) {
    if(item == null) {
        getFragmentManager().popBackStack();
        return null;
    }
    ...
}

I add most fragments like this:

getSupportFragmentManager().beginTransaction()
    .replace(R.id.container, TheFragment.newInstance(type))
    .addToBackStack(null)
    .commit();

Edit

Never allowing back to navigate down the hierarchy avoids the problem in this particular case, but the general problem I would like to solve is this:

Say the items have a 'next' option and that there is also a 'Manage Items' view that can be reached while navigating the items.

Going back from 'Manage Items' I would expect to jump back to the previous visited item.

So I navigate A -> B -> Manage Items.

From 'Manage Items' I delete item A and press back, popping to the fragment for item B, which is fine. Pressing back again will load up the fragment pointing to the deleted item A, causing trouble when I try to load the now deleted data from DB.

The only workaround I have at the moment is to detect the problem in onCreateView when recreating the fragment for the missing item, and 'escape' using popBackStack()

Answer 1

Do you really need to maintain the back stack when you return to your list? I would have expected the back stack to be cleared at that point, similar to how a back key on the Android home screen doesn't take you to the previous app that was running on the device.

You could accomplish this by clearing the back stack in your list fragment's onResume. If the list is always the starting point, you can just use:

FragmentManager fm = getFragmentManager();
while (fm.popBackStackImmediate()) {
}

If you sometimes need to preserve the back stack before you get to the list, then you can use one of the other varieties of popBackStackImmediate that specifies an ID or name to return to.