Question

I’m currently working on a project in which I need something like the following:

- MainGroup 1 (Expandable)
  - SubGroup 1 (Expandable)
    - SubSubGroup 1 (Expandable)
      - Child View
      - Child View
      - ...
    - SubSubGroup 2 (Expandable)
      - Child View
      - Child View
      - ...
  - SubGroup 2 (Expandable)
    - SubSubGroup 3 (Expandable)
      - Child View
      - ...
    - SubSubGroup 4 (Expandable)
      - Child View
      - ...
  - SubGroup 3 (Expandable)
    - Child View
    - ...
- MainGroup 2 (Expandable)
  - ...

At most it would be an ExpandableListView inside an ExpandableListView inside an ExpandableListView – so 3 layers of ExpandableListView:

• MainGroup would only hold other ExpandableListView.
• SubGroup would hold other ExpandableListView except for the last two, which will allways just be ChildViews. (I’m thinking those two could just be substituted with the one for SubSubGroup)
• SubSubGroup would allways hold ChildViews.

My problem is that I think I fail to understand the basic principles of how the ExpandableListView layouts it’s children. I’ve looked at examples like this, but can’t get my head around the functionality.

I’ve tried simply adding an ExpandableListView as a child in another – but something doesn’t work as only the first item of the inner ExpandableListView is visible if you expand one of the outer groups. I can however by setting the height of the outer groups container manually make it big enough to show all items in the inner ExpandableListView. To be optimal, calculation of height should of course be done on the fly.

So, to get to some more solid questions:

• Can someone give me an explanation of the ExpandableListView “lifecycle” (by this I mean instantation, re-use of views, expand/collapse listeners) including:
  • How and when is an ExpandableListView notified that a child is expanded/collapsed?
  • How does the ExpandableListView know how much space to make for all children to fit into a group container?
• How much benefit is there in using the ExpandableListView to create the above, compared to just mixing together my own solution using some LinearLayouts and some OnClickListeners?

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Edit

For my last question I might note that there can be anywhere from 1 to 20+ MainGroups.

Answer 1

First of all, let me recommend you GrepCode site. It has sources of Android SDK classes. Thanks for them, I’ve found out base principles of AdapterViews (I gave you a link to ExpandableListView, but it’s better if you research not only it, but its class-parents as well).

Now, your questions and my answers:

How and when is an ExpandableListView notified that a child is
expanded/collapsed?

See method handleItemClick(View v, int position, long id)

How does the ExpandableListView know how much space to make for all
children to fit into a group container?

I didn’t research this question well, but as far as I know, it’s made by the method requestLayout(). Also we found out that one scrollable View cannot be embedded into another scrollable View. (It’s wide-known mistake: to put ListView into ScrollView or ListView into ExpandableListView).

How much benefit is there in using the ExpandableListView to create
the above, compared to just mixing together my own solution using some
LinearLayouts and some OnClickListeners?

AdapterViews are faster. But your construction is too complex even for ExpandableListView. You may use 2 solutions.

1. Guru-solution: if you’re professional of designing your own
   Views/ViewGroups from the scratch (I mean, you understand methods
   requestLayout(), dispatchDraw() and so on), then write your own
   GrandExpandableListAdapter with 3 levels.
2. Medium-solution: use ExpandableListAdapter for first 2 levels and use LinearLayouts for
   3rd level.