| An activity that displays an expandable list of items by binding to a data
source implementing the ExpandableListAdapter, and exposes event handlers
when the user selects an item.
ExpandableListActivity hosts a
{@link android.widget.ExpandableListView ExpandableListView} object that can
be bound to different data sources that provide a two-levels of data (the
top-level is group, and below each group are children). Binding, screen
layout, and row layout are discussed in the following sections.
Screen Layout
ExpandableListActivity has a default layout that consists of a single,
full-screen, centered expandable list. However, if you desire, you can
customize the screen layout by setting your own view layout with
setContentView() in onCreate(). To do this, your own view MUST contain an
ExpandableListView object with the id "@android:id/list" (or
{@link android.R.id#list} if it's in code)
Optionally, your custom view can contain another view object of any type to
display when the list view is empty. This "empty list" notifier must have an
id "android:empty". Note that when an empty view is present, the expandable
list view will be hidden when there is no data to display.
The following code demonstrates an (ugly) custom screen layout. It has a list
with a green background, and an alternate red "no data" message.
<?xml version="1.0" encoding="UTF-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:paddingLeft="8dp"
android:paddingRight="8dp">
<ExpandableListView android:id="@id/android:list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#00FF00"
android:layout_weight="1"
android:drawSelectorOnTop="false"/>
<TextView android:id="@id/android:empty"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#FF0000"
android:text="No data"/>
</LinearLayout>
Row Layout
The {@link ExpandableListAdapter} set in the {@link ExpandableListActivity}
via {@link #setListAdapter(ExpandableListAdapter)} provides the {@link View}s
for each row. This adapter has separate methods for providing the group
{@link View}s and child {@link View}s. There are a couple provided
{@link ExpandableListAdapter}s that simplify use of adapters:
{@link SimpleCursorTreeAdapter} and {@link SimpleExpandableListAdapter}.
With these, you can specify the layout of individual rows for groups and
children in the list. These constructor takes a few parameters that specify
layout resources for groups and children. It also has additional parameters
that let you specify which data field to associate with which object in the
row layout resource. The {@link SimpleCursorTreeAdapter} fetches data from
{@link Cursor}s and the {@link SimpleExpandableListAdapter} fetches data
from {@link List}s of {@link Map}s.
Android provides some standard row layout resources. These are in the
{@link android.R.layout} class, and have names such as simple_list_item_1,
simple_list_item_2, and two_line_list_item. The following layout XML is the
source for the resource two_line_list_item, which displays two data
fields,one above the other, for each list row.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView android:id="@+id/text1"
android:textSize="16sp"
android:textStyle="bold"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
<TextView android:id="@+id/text2"
android:textSize="16sp"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
You must identify the data bound to each TextView object in this layout. The
syntax for this is discussed in the next section.
Binding to Data
You bind the ExpandableListActivity's ExpandableListView object to data using
a class that implements the
{@link android.widget.ExpandableListAdapter ExpandableListAdapter} interface.
Android provides two standard list adapters:
{@link android.widget.SimpleExpandableListAdapter SimpleExpandableListAdapter}
for static data (Maps), and
{@link android.widget.SimpleCursorTreeAdapter SimpleCursorTreeAdapter} for
Cursor query results.
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