Which approach is better for Delete confirmation when the operation may fail?

Question

I'm developing an Android application where I have entities A and sub-entities B. An A can have multiple Bs associated with it. (There's a database check for referential integrity).

I'm planning to implement a delete Action bar button with a trash icon. Bear in mind that checking for relationships may take time (asynchronously). Which of the following flows (or anything you can think of) would be better?

1. Post-confirm error checking

   a) User clicks the delete button

   b) User is asked if (s)he wants to delete the A (yes/no confirm)

   c) App displays: Sorry, can't delete A, it still has Bs associated to it
   (implying that (s)he has to delete all Bs first, but no shortcut to that)

2. Pre-confirm error checking

   a) User clicks the delete button

   b) App displays: Sorry, can't delete A, it still has Bs associated to it
   (implying that (s)he has to delete all Bs first, but no shortcut to that)

3. Pre-click error checking

   a) User can't click the delete button it's not shown or disabled
   (how would (s)he tell why it's not there?)

4. Post double-confirm

   a) User clicks the delete button

   b) User is asked if (s)he wants to delete (yes/no confirm)

   c) App displays: Sorry, can't delete A, it still has Bs associated to it, do you want to delete these Bs as well?

5. Flexible confirmation

   a) User clicks the delete button
   Optionally: the delete icon changes based on any Bs associated to the current A

   b) User is asked if (s)he wants to delete A and all Bs associated with it (yes/no confirm)
   Optionally: the all Bs associated with it part only shows if there are any.

Answer 1

Suggestion #5 sort of defeats the question.

If it's possible to delete "daughter" (don't know if this is proper lingo) Bs along with "parent" A, why not always suggest that?

On the confirmation dialog, alert that the current action will result in multiple entities (A and Bs) being deleted (list daughter Bs if possible) and confirm to delete the entire branch.

Answer 2

I would have the Delete button open a dialog box (modal window) that has a confirm message (if Delete is enabled) or a 'Sorry but you cannot delete this' message (if Delete is disabled).

Disabling the button is also a good choice, you could communicate why it's disabled with a tooltip on hover. Didn't notice OP is discussing an Android application.

Answer 3

N.B.: I'm assuming this app is backed up by a database on a server. If it's not, please read 'server-side script' as 'separate process' or 'other method' as appropriate.

What you're going to need here is a mixture. I recommend methods 3 and 4 that you already have. I don't know how you're displaying the entities but I'm going to assume it's in a list with select checkboxes next to each entry.

Process

• When a checkbox is selected, you call a method to check for sub-entities. You save the result. Of course, if the user deslects the checkbox you can cancel the check. This means that when you want to know about sub-entities, it's all already there, no further checking is necessary.
• When the delete button is clicked, this calls a server-side script. This pops the confirm dialog, which has a message according to the sub-entity state, as below. This then implements the action selected by the user (usually OK or Cancel but may be 'delete B then A' as below)

Messages

The confirm dialog should be flexible. It should ask the user whether she wants to delete the entity; if it has sub-entities, it should say it can't delete A but does she want to delete Bs then A?

You could still disable the delete button if you do your pre-click checking as described here. However, if you do, on tap it should display a tooltip that explains briefly why it is disabled, such as "The selected entity/entities have still got sub-entities and cannot be deleted.'

Hope this helps.