java.lang.Object | |||||
↳ | android.content.Context | ||||
↳ | android.content.ContextWrapper | ||||
↳ | android.view.ContextThemeWrapper | ||||
↳ | android.app.Activity | ||||
↳ | android.app.ListActivity |
Known Direct Subclasses
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An activity that displays a list of items by binding to a data source such as an array or Cursor, and exposes event handlers when the user selects an item.
ListActivity hosts a 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 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="match_parent" android:layout_height="match_parent" android:paddingLeft="8dp" android:paddingRight="8dp"> <ListView android:id="@id/android:list" android:layout_width="match_parent" android:layout_height="match_parent" android:background="#00FF00" android:layout_weight="1" android:drawSelectorOnTop="false"/> <TextView android:id="@id/android:empty" android:layout_width="match_parent" android:layout_height="match_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
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="match_parent" android:layout_height="wrap_content" android:orientation="vertical"> <TextView android:id="@+id/text1" android:textSize="16sp" android:textStyle="bold" android:layout_width="match_parent" android:layout_height="wrap_content"/> <TextView android:id="@+id/text2" android:textSize="16sp" android:layout_width="match_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 ListAdapter
interface.
Android provides two standard list adapters:
SimpleAdapter
for static data (Maps),
and 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 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 = this.getContentResolver().query(People.CONTENT_URI, null, null, null, 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[] {android.R.id.text1, android.R.id.text2}); // Parallel array of which template objects to bind to those columns.
// Bind to our new adapter.
setListAdapter(adapter);
}
}
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From class
android.app.Activity
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From class
android.content.Context
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From class
android.app.Activity
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Public Constructors | |||||||||||
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Public Methods | |||||||||||
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Get the ListAdapter associated with this activity's ListView.
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Get the activity's list view widget.
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Get the cursor row ID of the currently selected list item.
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Get the position of the currently selected list item.
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Updates the screen state (current list and other views) when the
content changes.
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Provide the cursor for the list view.
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Set the currently selected list item to the specified
position with the adapter's data
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Protected Methods | |||||||||||
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Perform any final cleanup before an activity is destroyed.
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This method will be called when an item in the list is selected.
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Ensures the list view has been created before Activity restores all
of the view states.
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From class
android.app.Activity
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From class
android.view.ContextThemeWrapper
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From class
android.content.ContextWrapper
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From class
android.content.Context
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From class
java.lang.Object
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From interface
android.content.ComponentCallbacks
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From interface
android.view.KeyEvent.Callback
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From interface
android.view.LayoutInflater.Factory
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From interface
android.view.LayoutInflater.Factory2
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From interface
android.view.View.OnCreateContextMenuListener
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From interface
android.view.Window.Callback
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Get the ListAdapter associated with this activity's ListView.
Get the cursor row ID of the currently selected list item.
Get the position of the currently selected list item.
Updates the screen state (current list and other views) when the content changes.
Provide the cursor for the list view.
Set the currently selected list item to the specified position with the adapter's data
Perform any final cleanup before an activity is destroyed. This can
happen either because the activity is finishing (someone called
finish()
on it, or because the system is temporarily destroying
this instance of the activity to save space. You can distinguish
between these two scenarios with the isFinishing()
method.
Note: do not count on this method being called as a place for
saving data! For example, if an activity is editing data in a content
provider, those edits should be committed in either onPause()
or
onSaveInstanceState(Bundle)
, not here. This method is usually implemented to
free resources like threads that are associated with an activity, so
that a destroyed activity does not leave such things around while the
rest of its application is still running. There are situations where
the system will simply kill the activity's hosting process without
calling this method (or any others) in it, so it should not be used to
do things that are intended to remain around after the process goes
away.
Derived classes must call through to the super class's implementation of this method. If they do not, an exception will be thrown.
This method will be called when an item in the list is selected. Subclasses should override. Subclasses can call getListView().getItemAtPosition(position) if they need to access the data associated with the selected item.
l | The ListView where the click happened |
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v | The view that was clicked within the ListView |
position | The position of the view in the list |
id | The row id of the item that was clicked |
Ensures the list view has been created before Activity restores all of the view states.
state | the data most recently supplied in onSaveInstanceState(Bundle) . |
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