Android Cursor自动更新的实现和原理

原文链接：http://www.sxrczx.com/pages/kohoh1992.github.io/cursor-auto-sync/index_1431878338570.html

在Android日常开发中，时常会请求数据到Cursor，然后再通过Cursor获取数据。像SQLiteDatabase和ContentProvider都使用了Cursor。在这些应用中，往往希望当数据发生改变时，Cursor也会自动的更新数据。这篇文章，我就会向你阐述如何通过Android自身的API实现Cursor的自动更新。另外我还将向你阐述这背后的原理。通过这些原理你可以举一反三的实现更为广泛的自动跟新。

文章中的代码

可以在https://github.com/KOHOH1992/CursorSyncDemo中找到文章中出现的代码

该项目共有4个分支。use_provider分支介绍了使用ContentProvider实现Cursor同步更新的方法。use_database分支介绍了不使用ContentProvider实现Cursor同步更新的方法。use_adapter分支介绍了不使用Loader实现Cursor同步更新的方法。

Cursor自动更新的实现

前提

首先假设项目使用了如下的前提

数据存储在SqliteDataBase当中

通对ContentProvider的请求，获取封装了数据的Cursor

使用CursorLoader加载数据

使用AdapterView和CursorAdapter显示数据

定义同步标志

static final Uri SYNC_SIGNAL_URI = Uri.parse("content://com.kohoh.cursorsyncdemo/SYNC_SIGNAL");

在ContentProvider的query中设置NotificationUri

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[]
selectionArgs,String sortOrder) {
SQLiteDatabase database = sqLiteOpenHelper.getReadableDatabase();
Cursor cursor = database.query(ContactContract.CONTACT_TABLE, projection,
selection,selectionArgs, null, null, sortOrder);
//设置NotificationUri
cursor.setNotificationUri(contentResolver, ContactContract.SYNC_SIGNAL_URI);
return cursor;
}

在ContentProvider的insert，update，delete中触发NotificationUri

@Override
public Uri insert(Uri uri, ContentValues values) {
SQLiteDatabase database = sqLiteOpenHelper.getWritableDatabase();
long id = database.insert(ContactContract.CONTACT_TABLE, null, values);

if (id >= 0) {
//触发NotificationUri
contentResolver.notifyChange(ContactContract.SYNC_SIGNAL_URI, null);
}

return uri.withAppendedPath(ContactContract.CONTACT_URI, String.valueOf(id));
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
SQLiteDatabase database = sqLiteOpenHelper.getWritableDatabase();
int result = database.update(ContactContract.CONTACT_TABLE, values,
selection, selectionArgs);

if (result > 0) {
//触发NotificationUri
contentResolver.notifyChange(ContactContract.SYNC_SIGNAL_URI, null);
}

return result;
}
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
SQLiteDatabase database = sqLiteOpenHelper.getWritableDatabase();
int result = database.delete(ContactContract.CONTACT_TABLE, selection,
selectionArgs);

if (result > 0) {
//触发NotificationUri
contentResolver.notifyChange(ContactContract.SYNC_SIGNAL_URI, null);
}

return result;
}

CursorLoader

ForceLoadContentObserver mObserver;

public Cursor loadInBackground() {
...
try {
//不过多解释，耗时的查询操作
Cursor cursor = getContext().getContentResolver().query(mUri, mProjection, mSelection,
mSelectionArgs, mSortOrder, mCancellationSignal);
if (cursor != null) {
try {
// Ensure the cursor window is filled.
cursor.getCount();
//给Cursor设置观察者；ContentProvider通知Cursor的观察者数据发生了改变，
//Cursor通知CursorLoader的观察者数据发生了改变，CursorLoader通过ContentProvider重新加载新的数据
cursor.registerContentObserver(mObserver);
//cursor.setNotificationUri(getContext().getContentResolver(), otificationUri);//给Cursor设置要观察的URI
} catch (RuntimeException ex) {
cursor.close();
throw ex;
}
}
return cursor;
}
}

Cursor的实现原理

Android的Cursor自动更新是通过观察者模式实现的，整个过程如下图所示



通过ContentPorvider和ContentResolver使得数据发生了改变

ContentProvider通知Cursor的观察者数据发生了改变

Cursor通知CursorLoader的观察者数据发生了改变

CursorLoader通过ContentProvider加载新的数据

ContentPovider向DataBase请求新的数据

CursorLoader调用CursorAdapter#changeCursor,用封装了新数据的Cursor替换旧的Cursor

CursorAdapter告知AdapterView的观察者有新的数据

AdapterView重新加载并显示数据

在Android的android.database包下，有一个ContentObserver。Android正是通过他来实现观察者模式的。当数据改变之后，观察者会将数据改变的消息通知相应的对象，进而做出反馈。在代码中，当数据改变之后，我会调用ContentResolver#notifyChange，发出ContactContract.SYNC_SIGNAL_URI信号，通知数据发生了改变。而在此之前，从ContentProvider#query中获得的Cursor已经通过Cursor#setNotificationUri对ContactContract.SYNC_SIGNAL_URI信号进行了监视。当该信号出现，Cursor就会将信息改变的消息告诉CursorLoader的观察者（在此之前CursorLoader已经对该Cursor设立了观察者）。CursorLoader会开始重新开始加载数据。当数据加载成功，CursorLoader会通过CursorAdapter#changeCursor设置封装了新数据的Cursor。而后CursorAdapter又会通知AdapterView的观察者数据发生了改变（在此之前AdapterView已经对CursorAdapter设立了观察者）。最后AdapterView就会重新加载并显示新的数据。



在整个过程当中，我要做的就是在改变数据时发出信号，对封装数据的Cursor设置需要监视的信号。具体的说就是在query中调用Cursor#setNotificationUri，在insert、update、delete中调用ContentResolver#notifyChange。这里需要补充的是Cursor和ContentResolver的信号机制同样是通过观察者模式实现的。

其他的实现方式

这里要介绍的其他的实现方式，依旧是通过观察者模式实现的。区别在于是否使用ContentProvider和CursorLoader

不使用ContentProvider

在开发过程中，如果数据不用于应用之间的共享，使用ContentProvider似乎有一些多余。然而Android提供的CursorLoader的API必须通过ContentProvider才能实现数据加载和数据同步更新。但是你任然可以在不使用ContentProvider的情况下实现Cursor的自动更新。你需要做的只是在你的Loader中加入下面的代码

// 实例化一个全局的ForceLoadContentObserver
ForceLoadContentObserver mObserver = new ForceLoadContentObserver();
@Override
public Cursor loadInBackground() {
SQLiteDatabase database = mSqLiteOpenHelper.getReadableDatabase();
Cursor cursor = database.query(mTable, mColumns, mSelection, mSelectionArgs,
mGroupBy,mHaving, mOrderBy);
if (cursor != null) {
cursor.getCount();
// 对Cursor设立观察者
cursor.registerContentObserver(mObserver);
// 设置Cursor的观察信号
cursor.setNotificationUri(getContext().getContentResolver(),
mNotificationUri);
}
return cursor;
}

ForceLoadContentObserver是Loader的内部类。当观察到数据发生变化之后，该类会调用Loader#forceLoad，进而开始重新加载数据。另外你也可以直接使用我项目中的DatabaseLoader。该类是我参照CursorLoader编写的一个工具，通过它你可以绕过ContentProvider，直接请求Database。

不使用Loader

如果你不想要使用Loader（我非常不赞成你这么做），你可以通过如下的代码实现Cursor的同步更新。

// 使用CursorAdapter.FLAG_AUTO_REQUERY标志
adapter = new SimpleCursorAdapter(this, R.layout.contact_item, null, from, to,
CursorAdapter.FLAG_AUTO_REQUERY);
private void loadData() {
SQLiteOpenHelper sqliteOpenHelper = ContactContract.getSqliteOpenHelper(this);
SQLiteDatabase database = sqliteOpenHelper.getReadableDatabase();
String[] columns = {ContactContract._ID, ContactContract.NAME,
ContactContract.PHONE};
Cursor cursor = database.query(ContactContract.CONTACT_TABLE, columns, null,
null, null,null, null);
//设置NotificationUri
cursor.setNotificationUri(this.getContentResolver(),
ContactContract.SYNC_SIGNAL_URI);
adapter.changeCursor(cursor);
}

这里的关键在于，在实例化CursorAdapter时使用了CursorAdapter.FLAGAUTOREQUERY标志。当使用该标志后，每当收到数据更新的消息，CursorAdapter就会自己调用CursorAdapter#requery重新加载数据。然而整个加载过程会再UI线程中发生，这很有可能会使得程序运行部流畅。正是因为这个原因该方法以及被Android设置为Deprecated了。因此如果有可能，我还是推荐你使用Loader。

ContactContract.java

package com.kohoh.cursorsyncdemo;

import android.content.ContentValues;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;
import android.provider.BaseColumns;

import com.google.common.base.Preconditions;
import com.google.common.base.Strings;

/**
* Created by kohoh on 14-11-3.
*/
public class ContactContract implements BaseColumns {

static final int DATABSE_VERSION = 1;
static final String DATABASE_NAME = "contact.db";

static final String CONTACT_TABLE = "contact";
static final String NAME = "name";
static final String PHONE = "phone";

static final String AUTHORITY = "com.kohoh.cursorsyncdemo";
static final Uri BASE_URI = Uri.parse("content://" + AUTHORITY);
static final Uri CONTACT_URI = Uri.withAppendedPath(BASE_URI, "contact");
static final Uri SYNC_SIGNAL_URI = Uri.withAppendedPath(BASE_URI, "SYNC_SIGNAL_URI");

static public ContactDatabaseHelper getSqliteOpenHelper(Context context) {
return new ContactDatabaseHelper(context);
}

static class ContactDatabaseHelper extends SQLiteOpenHelper {
public ContactDatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABSE_VERSION);
}

static public long addContact(SQLiteDatabase database, String name, int phone) {
Preconditions.checkNotNull(database);
Preconditions.checkNotNull(phone);
Preconditions.checkArgument(!Strings.isNullOrEmpty(name));

ContentValues contentValues = new ContentValues();
contentValues.put(NAME, name);
contentValues.put(PHONE, phone);

return database.insert(CONTACT_TABLE, null, contentValues);
}

static public void deleteContact(Context context, long id) {
Preconditions.checkNotNull(context);
Preconditions.checkArgument(id >= 0);

ContactContract.ContactDatabaseHelper databaseHelper = ContactContract.
getSqliteOpenHelper(context);
SQLiteDatabase databasea = databaseHelper.getWritableDatabase();
String where = ContactContract._ID + " = ?";
String[] whereArgs = {String.valueOf(id)};
databasea.delete(ContactContract.CONTACT_TABLE, where, whereArgs);
context.getContentResolver().notifyChange(ContactContract.SYNC_SIGNAL_URI, null);
}

@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE " + CONTACT_TABLE + "( " +
_ID + " INTEGER PRIMARY KEY," +
NAME + " TEXT," +
PHONE + " INTERGER)");

addContact(db, "aaa", 111);
addContact(db, "bbb", 222);
addContact(db, "ccc", 333);
addContact(db, "ddd", 444);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}
}
}

ContactProvider.java

package com.kohoh.cursorsyncdemo;

import android.content.ContentProvider;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;

/**
* Created by kohoh on 14-11-3.
*/
public class ContactProvider extends ContentProvider {
private SQLiteOpenHelper sqLiteOpenHelper;
private ContentResolver contentResolver;
private UriMatcher uriMatcher;

final private int DIR = 0;
final private int ITEM = 1;

@Override
public boolean onCreate() {
sqLiteOpenHelper = ContactContract.getSqliteOpenHelper(getContext());
contentResolver = getContext().getContentResolver();
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(ContactContract.AUTHORITY, "contact", DIR);
uriMatcher.addURI(ContactContract.AUTHORITY, "contact/#", ITEM);
return true;
}

@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
String sortOrder) {
if (uriMatcher.match(uri) == ITEM) {
return null;
}

SQLiteDatabase database = sqLiteOpenHelper.getReadableDatabase();
Cursor cursor = database.query(ContactContract.CONTACT_TABLE, projection, selection,
selectionArgs, null, null, sortOrder);
cursor.setNotificationUri(contentResolver, ContactContract.SYNC_SIGNAL_URI);
return cursor;
}

@Override
public String getType(Uri uri) {
switch (uriMatcher.match(uri)) {
case ITEM:
return "vnd.android.cursor.item/vnd.con.kohoh.cursorsyncdemo";
case DIR:
return "vnd.android.cursor.dir/vnd.con.kohoh.cursorsyncdemo";
default:
return null;
}
}

@Override
public Uri insert(Uri uri, ContentValues values) {
if (uriMatcher.match(uri) == ITEM) {
return null;
}

SQLiteDatabase database = sqLiteOpenHelper.getWritableDatabase();
long id = database.insert(ContactContract.CONTACT_TABLE, null, values);

if (id >= 0) {
contentResolver.notifyChange(ContactContract.SYNC_SIGNAL_URI, null);
}

return uri.withAppendedPath(ContactContract.CONTACT_URI, String.valueOf(id));
}

@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
if (uriMatcher.match(uri) == ITEM) {
return 0;
}

SQLiteDatabase database = sqLiteOpenHelper.getWritableDatabase();
int result = database.delete(ContactContract.CONTACT_TABLE, selection, selectionArgs);

if (result > 0) {
contentResolver.notifyChange(ContactContract.SYNC_SIGNAL_URI, null);
}

return result;
}

@Override
public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
if (uriMatcher.match(uri) == ITEM) {
return 0;
}

SQLiteDatabase database = sqLiteOpenHelper.getWritableDatabase();
int result = database.update(ContactContract.CONTACT_TABLE, values, selection, selectionArgs);

if (result > 0) {
contentResolver.notifyChange(ContactContract.SYNC_SIGNAL_URI, null);
}

return result;
}
}

DatabaseLoader.java

package com.kohoh.cursorsyncdemo;

import android.content.AsyncTaskLoader;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.net.Uri;

/**
* Created by kohoh on 14-11-3.
*/
public class DatabaseLoader extends AsyncTaskLoader<Cursor> {
final ForceLoadContentObserver mObserver;

Uri mNotificationUri;
String mTable;
String[] mColumns;
String mSelection;
String[] mSelectionArgs;
String mGroupBy;
String mHaving;
String mOrderBy;
SQLiteOpenHelper mSqLiteOpenHelper;

Cursor mCursor;

public DatabaseLoader(Context context) {
super(context);
this.mObserver = new ForceLoadContentObserver();
}

public DatabaseLoader(Context context, SQLiteOpenHelper sqLiteOpenHelper, Uri mNotificationUri,
String mTable, String[] mColumns, String mSelection, String[] mSelectionArgs,
String mGroupBy, String mHaving, String mOrderBy) {
super(context);
this.mNotificationUri = mNotificationUri;
this.mTable = mTable;
this.mColumns = mColumns;
this.mSelection = mSelection;
this.mSelectionArgs = mSelectionArgs;
this.mGroupBy = mGroupBy;
this.mHaving = mHaving;
this.mOrderBy = mOrderBy;
this.mSqLiteOpenHelper = sqLiteOpenHelper;
this.mObserver = new ForceLoadContentObserver();
}

@Override
public Cursor loadInBackground() {
SQLiteDatabase database = mSqLiteOpenHelper.getReadableDatabase();
Cursor cursor = database.query(mTable, mColumns, mSelection, mSelectionArgs, mGroupBy,
mHaving, mOrderBy);
if (cursor != null) {
cursor.getCount();
cursor.registerContentObserver(mObserver);
cursor.setNotificationUri(getContext().getContentResolver(), mNotificationUri);
}
return cursor;
}

@Override
public void deliverResult(Cursor cursor) {
if (isReset()) {
if (cursor != null) {
cursor.close();
}
return;
}
Cursor oldCursor = mCursor;
mCursor = cursor;

if (isStarted()) {
super.deliverResult(cursor);
}

if (oldCursor != null && oldCursor != cursor && !oldCursor.isClosed()) {
oldCursor.close();
}
}

@Override
protected void onStartLoading() {
if (mCursor != null) {
deliverResult(mCursor);
}
if (takeContentChanged() || mCursor == null) {
forceLoad();
}
}

@Override
protected void onStopLoading() {
// Attempt to cancel the current load task if possible.
cancelLoad();
}

@Override
public void onCanceled(Cursor cursor) {
if (cursor != null && !cursor.isClosed()) {
cursor.close();
}
}

@Override
protected void onReset() {
super.onReset();

onStopLoading();

if (mCursor != null && !mCursor.isClosed()) {
mCursor.close();
}
mCursor = null;
}

public SQLiteOpenHelper getSqLiteOpenHelper() {
return mSqLiteOpenHelper;
}

public void setSqLiteOpenHelper(SQLiteOpenHelper mSqLiteOpenHelper) {
this.mSqLiteOpenHelper = mSqLiteOpenHelper;
}

public Uri getNotificationUri() {
return mNotificationUri;
}

public void setNotificationUri(Uri mNotificationUri) {
this.mNotificationUri = mNotificationUri;
}

public String getTable() {
return mTable;
}

public void setTable(String mTable) {
this.mTable = mTable;
}

public String[] getColumns() {
return mColumns;
}

public void setColumns(String[] mColumns) {
this.mColumns = mColumns;
}

public String getSelection() {
return mSelection;
}

public void setSelection(String mSelection) {
this.mSelection = mSelection;
}

public String[] getSelectionArgs() {
return mSelectionArgs;
}

public void setSelectionArgs(String[] mSelectionArgs) {
this.mSelectionArgs = mSelectionArgs;
}

public String getGroupBy() {
return mGroupBy;
}

public void setGroupBy(String mGroupBy) {
this.mGroupBy = mGroupBy;
}

public String getHaving() {
return mHaving;
}

public void setHaving(String mHaving) {
this.mHaving = mHaving;
}

public String getOrderBy() {
return mOrderBy;
}

public void setOrderBy(String mOrderBy) {
this.mOrderBy = mOrderBy;
}
}

use provider

package com.kohoh.cursorsyncdemo;

import android.app.Activity;
import android.app.LoaderManager;
import android.content.CursorLoader;
import android.content.Loader;
import android.database.Cursor;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

public class CursorSyncDemo extends Activity implements LoaderManager.LoaderCallbacks<Cursor> {

private ListView listView;
private SimpleCursorAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_cursor_sync_demo);

String[] from = {ContactContract.NAME, ContactContract.PHONE};
int[] to = {R.id.name, R.id.phone};

listView = (ListView) findViewById(R.id.lv);
adapter = new SimpleCursorAdapter(this, R.layout.contact_item, null, from, to,
CursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);
listView.setAdapter(adapter);

getLoaderManager().initLoader(0, null, this);

registerForContextMenu(listView);
}

@Override
public boolean onContextItemSelected(MenuItem item) {

switch (item.getItemId()) {
case R.id.delete:
AdapterView.AdapterContextMenuInfo menuInfo = (AdapterView.AdapterContextMenuInfo)
item.getMenuInfo();

ContactContract.ContactDatabaseHelper.deleteContact(this, menuInfo.id);
return true;
default:
return super.onContextItemSelected(item);
}
}

@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.contact_item_menu, menu);
}

@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
String[] projection = {ContactContract._ID, ContactContract.NAME, ContactContract.PHONE};
return new CursorLoader(this, ContactContract.CONTACT_URI, projection, null, null, null);
}

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
adapter.changeCursor(data);
}

@Override
public void onLoaderReset(Loader<Cursor> loader) {

}
}

use database

package com.kohoh.cursorsyncdemo;

import android.app.Activity;
import android.app.LoaderManager;
import android.content.Loader;
import android.database.Cursor;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

public class CursorSyncDemo extends Activity implements LoaderManager.LoaderCallbacks<Cursor> {

private ListView listView;
private SimpleCursorAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_cursor_sync_demo);

String[] from = {ContactContract.NAME, ContactContract.PHONE};
int[] to = {R.id.name, R.id.phone};

listView = (ListView) findViewById(R.id.lv);
adapter = new SimpleCursorAdapter(this, R.layout.contact_item, null, from, to,
CursorAdapter.FLAG_REGISTER_CONTENT_OBSERVER);
listView.setAdapter(adapter);
getLoaderManager().initLoader(0, null, this);

registerForContextMenu(listView);
}

@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
String[] columns = {ContactContract._ID, ContactContract.NAME, ContactContract.PHONE};

return new DatabaseLoader(this,
ContactContract.getSqliteOpenHelper(this),
ContactContract.SYNC_SIGNAL_URI,
ContactContract.CONTACT_TABLE,
columns,
null,
null,
null,
null,
null);
}

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
adapter.changeCursor(data);
}

@Override
public void onLoaderReset(Loader<Cursor> loader) {

}

@Override
public boolean onContextItemSelected(MenuItem item) {

switch (item.getItemId()) {
case R.id.delete:
AdapterView.AdapterContextMenuInfo menuInfo = (AdapterView.AdapterContextMenuInfo)
item.getMenuInfo();

ContactContract.ContactDatabaseHelper.deleteContact(this, menuInfo.id);
return true;
default:
return super.onContextItemSelected(item);
}
}

@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.contact_item_menu, menu);
}
}

use adapter

package com.kohoh.cursorsyncdemo;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

public class CursorSyncDemo extends Activity {

private ListView listView;
private SimpleCursorAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_cursor_sync_demo);

String[] from = {ContactContract.NAME, ContactContract.PHONE};
int[] to = {R.id.name, R.id.phone};

listView = (ListView) findViewById(R.id.lv);
adapter = new SimpleCursorAdapter(this, R.layout.contact_item, null, from, to,
CursorAdapter.FLAG_AUTO_REQUERY);
listView.setAdapter(adapter);

loadData();

registerForContextMenu(listView);
}

private void loadData() {
SQLiteOpenHelper sqliteOpenHelper = ContactContract.getSqliteOpenHelper(this);
SQLiteDatabase database = sqliteOpenHelper.getReadableDatabase();
String[] columns = {ContactContract._ID, ContactContract.NAME, ContactContract.PHONE};
Cursor cursor = database.query(ContactContract.CONTACT_TABLE, columns, null, null, null,
null, null);
cursor.setNotificationUri(this.getContentResolver(), ContactContract.SYNC_SIGNAL_URI);
adapter.changeCursor(cursor);
}

@Override
public boolean onContextItemSelected(MenuItem item) {

switch (item.getItemId()) {
case R.id.delete:
AdapterView.AdapterContextMenuInfo menuInfo = (AdapterView.AdapterContextMenuInfo)
item.getMenuInfo();

ContactContract.ContactDatabaseHelper.deleteContact(this, menuInfo.id);
return true;
default:
return super.onContextItemSelected(item);
}
}

@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.contact_item_menu, menu);
}
}