ListActivity

ListActivity hosts a {@link android.widget.ListView ListView} object that can be bound to different data sources, typically either an array or a Cursor holding query results. Binding, screen layout, and row layout are discussed in the following sections.

Screen Layout

ListActivity has a default layout that consists of a single, full-screen list in the center of the screen. 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 a ListView 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 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">

<ListView 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 id="@id/android:empty"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#FF0000"
android:text="No data"/>
</LinearLayout>

Row Layout

You can specify the layout of individual rows in the list. You do this by specifying a layout resource in the ListAdapter object hosted by the activity (the ListAdapter binds the ListView to the data; more on this later).

A ListAdapter constructor takes a parameter that specifies a layout resource for each row. It also has two additional parameters that let you specify which data field to associate with which object in the row layout resource. These two parameters are typically parallel arrays.

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 ListActivity's ListView object to data using a class that implements the {@link android.widget.ListAdapter ListAdapter} interface. Android provides two standard list adapters: {@link android.widget.SimpleAdapter SimpleAdapter} for static data (Maps), and {@link android.widget.SimpleCursorAdapter SimpleCursorAdapter} for Cursor query results.

The following code from a custom ListActivity demonstrates querying the Contacts provider for all contacts, then binding the Name and Company fields to a two line row layout in the activity's ListView.

public class MyListAdapter extends ListActivity {

@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);

// We'll define a custom screen layout here (the one shown above), but
// typically, you could just use the standard ListActivity layout.
setContentView(R.layout.custom_list_activity_view);

// Query for all people contacts using the {@link android.provider.Contacts.People} convenience class.
// Put a managed wrapper around the retrieved cursor so we don't have to worry about
// requerying or closing it as the activity changes state.
mCursor = People.query(this.getContentResolver(), null);
startManagingCursor(mCursor);

// Now create a new list adapter bound to the cursor.
// SimpleListAdapter is designed for binding to a Cursor.
ListAdapter adapter = new SimpleCursorAdapter(
this, // Context.
android.R.layout.two_line_list_item, // Specify the row template to use (here, two columns bound to the two retrieved cursor
rows).
mCursor, // Pass in the cursor to bind to.
new String[] {People.NAME, People.COMPANY}, // Array of cursor columns to bind to.
new int[]); // Parallel array of which template objects to bind to those columns.

// Bind to our new adapter.
setListAdapter(adapter);
}
}