The following is the first few sections of a chapter from The Busy Coder's Guide to Android Development, plus headings for the remaining major sections, to give you an idea about the content of the chapter.

Widget Catalog: ExpandableListView

Android does not have a “tree” widget, allowing users to navigate an arbitrary hierarchy of stuff. In large part, that is because such trees are difficult to navigate on small touchscreens with comparatively large fingers.

Android does have ExpandableListView, a subclass of ListView that supports a two-layer hierarchy: groups and children. Groups can be expanded to show their children or collapsed to hide them, and you can get control on various events for the groups or the children.

Key Usage Tips

Android offers an ExpandableListActivity as a counterpart to its ListActivity. However, it does not offer an ExpandableListFragment. This is not a major issue, as you can work with an ExpandableListView inside a regular Fragment yourself, just as you would for most other widgets not named ListView.

Rather than use a ListAdapter with ExpandableListView, you will use an ExpandableListAdapter, where you can control separate details for groups and children. These include:

In many cases, though, the complexity of managing groups and children will steer you down the path of extending BaseExpandableListAdapter and handling all of the view construction yourself. There are many methods that you will need to implement:

There are four major events that you will be able to respond to with respect to the user’s interaction with an ExpandableListView:

If you use setOnGroupClickListener() to be notified about clicks on a group, be sure to return false from your implementation of the onGroupClick() method required by the OnGroupClickListener interface. If you return true, you consume the click event, which prevents ExpandableListView from using that event to expand or collapse the group.

A Sample Usage

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Visual Representation

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