Android Layout-List View

This article translated from: http://developer.android.com/guide/topics/ui/layout/listview.html

Listview is a view group used to display the scrolling project list. It adapts to an adapter to automatically Insert list items. The adapter pulls content from queries such as arrays or databases and converts the results of each project into a view that can be placed in the list.

For how to use an adapter to automatically insert a view, see use an adapter to create a layout.

Use the loader

To avoid blocking the main thread of your application during query, using cursorloader asynchronous tasks to query cursor is a standard method. When cursorloader receives the cursor result, loadercallbacks receives a callback for the onloadfinished () method. This is where you use the new cursor to update your adapter, and then the List View displays the result.

Although cursorloader APIs are introduced for the first time in android3.0 (API level 11), these APIs are also valid in the supported class libraries. Therefore, in devices that support running android1.6 or above, your application can also be used.

For information on using loader to asynchronously load data, see the loaders guide.

Example

The following example uses listactivity. By default, it is an activity that contains only one listview layout element. It queries the contacts provider to obtain the list of names and phone numbers.

To use cursorloader to automatically load data to the list view, this activity implements the loadercallbacks interface.

Public class listviewloader extends listactivity

Implements loadermanager. loadercallbacks <cursor> {

// This is the adapter being used to display the list's data

Simplecursoradapter madapter;

// These are the contacts rows that we will retrieve

Static final string [] projection = new string [] {contactscontract. Data. _ id,

Contactscontract. Data. display_name };

// This is the select criteria

Static final string selection = "(" +

Contactscontract. Data. display_name + "notnull) and (" +

Contactscontract. Data. display_name + "! = ''))";

@ Override

Protected void oncreate (bundle savedinstancestate ){

Super. oncreate (savedinstancestate );

// Create a progress bar to display while the list Loads

Progressbar = new progressbar (this );

Progressbar. setlayoutparams (New layoutparams (layoutparams. wrap_content,

Layoutparams. wrap_content, gravity. Center ));

Progressbar. setindeterminate (true );

Getlistview (). setemptyview (progressbar );

// Must add the progress bar to the root of the layout

Viewgroup root = (viewgroup) findviewbyid (Android. R. Id. content );

Root. addview (progressbar );

// For the cursor adapter, specify which Columns go into which views

String [] fromcolumns = {contactscontract. Data. display_name };

Int [] toviews = {Android. R. Id. text1}; // The textview in simple_list_item_1

// Create an empty adapter we will use to display the loaded data.

// We pass NULL for the cursor, then update it in onloadfinished ()

Madapter = new simplecursoradapter (this,

Android. R. layout. simple_list_item_1, null,

Fromcolumns, toviews, 0 );

Setlistadapter (madapter );

// Prepare the loader. either re-connect with an existing one,

// Or start a new one.

Getloadermanager (). initloader (0, null, this );

}

// Called when a new loader needs to be created

Public loader <cursor> oncreateloader (int id, bundle ARGs ){

// Now create and return a cursorloader that will take care

// Creating a cursor for the data being displayed.

Return new cursorloader (this, contactscontract. Data. content_uri,

Projection, selection, null, null );

}

// Called when a previusly created loader has finished loading

Public void onloadfinished (loader <cursor> loader, cursor data ){

// Swap the new cursor in. (The framework will take care of closing

// Old cursor once we return .)

Madapter. swapcursor (data );

}

// Called when a previusly created loader is reset, making the data unavailable

Public void onloaderreset (loader <cursor> loader ){

// This is called when the last cursor provided to onloadfinished ()

// Above is about to be closed. We need to make sure we are no

// Longer using it.

Madapter. swapcursor (null );

}

@ Override

Public void onlistitemclick (listview L, view V, int position, long ID ){

// Do something when a list item is clicked

}

}

Note:In this example, You need to query the contacts provider. to execute this code, your application must apply for the read_contacts permission in the configuration file:

<uses-permission android:name="android.permission.READ_CONTACTS" />