Android Cursor自动更新的实现和原理

系统管理员 2022-07-12 21:07 849阅读 0赞

原文链接：[http://www.sxrczx.com/pages/kohoh1992.github.io/cursor-auto-sync/index\_1431878338570.html][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][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

![CursorLoader][]

*  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。

![CursorLoader][CursorLoader 1]

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);
        }
    }

![Android视频教程][Android]

[http_www.sxrczx.com_pages_kohoh1992.github.io_cursor-auto-sync_index_1431878338570.html]: http://www.sxrczx.com/pages/kohoh1992.github.io/cursor-auto-sync/index_1431878338570.html
[https_github.com_KOHOH1992_CursorSyncDemo]: https://github.com/KOHOH1992/CursorSyncDemo
[CursorLoader]: /images/20220713/c7d124b9f7b44279905d540f4dc22928.png
[CursorLoader 1]: /images/20220713/813a3984e3354258874d82cfddb50a1f.png
[Android]: /images/20220713/4a49751a15bc42a797a8dd6b5e6f7cc3.png