学步园

1. 概念：

    在HoneyComb3.0中提出了新的异步数据加载特性(ContentLoader)，它可以异步的从后台获取数据并更新UI界面。CursorLoader类是专门为此

    特性设计的，他允许程序通过ContentProvider异步的从数据中读取数据，并将获取的数据显示到UI界面中。

2. 效果图：

    （1）主操作界面，在Action|Bar中存在两个"快捷按钮"，如下图：

    （2）单击"加载按钮"后从数据库中动态的加载数据（当前数据库只添加了一条数据），如下图：

    （3）间隔5秒后继续从数据库中读取数据（数据库被动态的添加了数据，并调用ContentResovler的notifiyChange()方法，该方法不调5秒后不

            会加载数据）：

3. 功能实现：

    （1）主Activity代码：package com.focus.content.loader;<br /> import android.app.Activity;<br /> import android.app.FragmentManager;<br /> import android.os.Bundle;<br /> /**<br /> *<br /> * ContentLoader实例的入口Activity类。<br /> *<br /> * @author 马英才<br /> *<br /> */<br /> public class ContentLoaderActivity extends Activity {</p> <p> @Override<br /> public void onCreate(Bundle savedInstanceState) {<br /> super.onCreate(savedInstanceState);<br /> /**<br /> * 获取FragmentManager实例。<br /> */<br /> FragmentManager mFragmentManager = getFragmentManager();<br /> if (mFragmentManager.findFragmentById(android.R.id.content) == null) {<br /> /**<br /> * 创建ContentLoaderFragment,这是一个ListFragment,用于显示結果。<br /> */<br /> ContentLoaderFragment mContentLoaderFragment = new ContentLoaderFragment();</p> <p> /**<br /> * 通过FragmentManager向Activity中添加Fragment。<br /> */<br /> mFragmentManager.beginTransaction().add(android.R.id.content, mContentLoaderFragment).commit();<br /> }<br /> }</p> <p>}

    （2）查询結果显示器，ListFragment代码：package com.focus.content.loader;<br /> import android.app.ListFragment;<br /> import android.content.ContentResolver;<br /> import android.content.ContentValues;<br /> import android.os.AsyncTask;<br /> import android.os.Bundle;<br /> import android.view.Menu;<br /> import android.view.MenuInflater;<br /> import android.view.MenuItem;<br /> import android.widget.SimpleCursorAdapter;<br /> /**<br /> *<br /> * 显示从数据库中查询出的内容的Fragment,它是ListFragment,即：Fragment中包含一个ListView组件。<br /> *<br /> * @author 马英才<br /> *<br /> */<br /> public class ContentLoaderFragment extends ListFragment {<br /> static final int POPULATE_ID = Menu.FIRST;<br /> static final int CLEAR_ID = Menu.FIRST+1;<br /> private SimpleCursorAdapter mSimpleCursorAdapter;<br /> private AsyncTask<Void, Void, Void> mPopulatingTask;<br /> @Override<br /> public void onActivityCreated(Bundle savedInstanceState) {<br /> super.onActivityCreated(savedInstanceState);<br /> setHasOptionsMenu(true);<br /> /**<br /> * 渲染Adapter,即：给ListFragment中的ListView设置的Adapter实现。<br /> */<br /> mSimpleCursorAdapter = new SimpleCursorAdapter<br /> (<br /> getActivity(),<br /> android.R.layout.simple_list_item_1,<br /> null,<br /> new String[] { ContentLoaderConstant.COLUMN_NAME_DATA },<br /> new int[] { android.R.id.text1 },<br /> 0<br /> );</p> <p> /**<br /> * 给ListFragment中的ListView组件设置Adapter实现。<br /> */<br /> setListAdapter(mSimpleCursorAdapter);<br /> /**<br /> * 通过LoaderManager初始化ContentLoader,initLoader()方法的等三个参数是LoaderCallbacks实现，<br /> * 在Callbacks实现中创建ContentLoader实例，并设置多长时间通过ContentLoader去异步的加载数据，并刷新界面显示。<br /> */<br /> getLoaderManager().initLoader(0, null, new ContentLoaderCallBack(getActivity(), mSimpleCursorAdapter));<br /> }<br /> /**<br /> * 向ActionBar中添加"快捷按钮"。<br /> */<br /> @Override<br /> public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {<br /> menu.add(Menu.NONE, POPULATE_ID, 0, "Populate Letter").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);<br /> menu.add(Menu.NONE, CLEAR_ID, 0, "Clear").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM);<br /> }<br /> /**<br /> * 单击ActionBar中添加"快捷按钮"触发相应事件。<br /> */<br /> @Override<br /> public boolean onOptionsItemSelected(MenuItem item) {<br /> final ContentResolver cr = getActivity().getContentResolver();<br /> switch (item.getItemId()) {<br /> case POPULATE_ID :</p> <p> if (mPopulatingTask != null) {<br /> mPopulatingTask.cancel(false);<br /> }</p> <p> /**<br /> * 异步的通过ContentProvider向数据库中添加数据。<br /> */<br /> mPopulatingTask = new AsyncTask<Void, Void, Void>() {</p> <p> @Override<br /> protected Void doInBackground(Void... params) {<br /> for (char c = 'A'; c <= 'K'; c++) {<br /> if (isCancelled()) {<br /> break;<br /> }</p> <p> StringBuilder builder = new StringBuilder("Data ");<br /> builder.append(c);<br /> ContentValues values = new ContentValues();<br /> values.put(ContentLoaderConstant.COLUMN_NAME_DATA, builder.toString());<br /> cr.insert(ContentLoaderConstant.CONTENT_URI, values);</p> <p> try {<br /> Thread.sleep(1000);<br /> } catch (InterruptedException e) {</p> <p> }</p> <p> }<br /> return null;<br /> }<br /> };</p> <p> mPopulatingTask.execute((Void [])null);</p> <p> return true;<br /> case CLEAR_ID:</p> <p> if (mPopulatingTask != null) {<br /> mPopulatingTask.cancel(false);<br /> mPopulatingTask = null;<br /> }<br /> /**<br /> * 异步的通过ContentProvider清除数据库中的数据。<br /> */<br /> AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {<br /> @Override<br /> protected Void doInBackground(Void... params) {<br /> cr.delete(ContentLoaderConstant.CONTENT_URI, null, null);<br /> return null;<br /> }<br /> };</p> <p> task.execute((Void[])null);</p> <p> return true;<br /> default:<br /> return super.onOptionsItemSelected(item);</p> <p> }<br /> }<br /> } 

    （3）ContentLoader回调方法：package com.focus.content.loader;<br /> import android.app.LoaderManager;<br /> import android.content.Context;<br /> import android.content.CursorLoader;<br /> import android.content.Loader;<br /> import android.database.Cursor;<br /> import android.os.Bundle;<br /> import android.widget.SimpleCursorAdapter;<br /> /**<br /> *<br /> * LoaderCallbacks实现，创建CursorLoader,根据设置的更新时间，异步的从后台数据库搜索数据，并通过Adapter更新显示列表。<br /> *<br /> * @author 马英才<br /> *<br /> */<br /> public class ContentLoaderCallBack implements LoaderManager.LoaderCallbacks<Cursor> {<br /> private Context mContext;</p> <p> private SimpleCursorAdapter mSimpleCursorAdapter;</p> <p> public ContentLoaderCallBack (Context mContext, SimpleCursorAdapter mSimpleCursorAdapter) {<br /> this.mContext = mContext;<br /> this.mSimpleCursorAdapter = mSimpleCursorAdapter;<br /> }</p> <p> /**<br /> * 创建CursorLoader(异步数据加载器)，并设置更新时间，这个Loader会根据更新时间从ContentProvider中加载数据。<br /> */<br /> @Override<br /> public Loader<Cursor> onCreateLoader(int id, Bundle args) {<br /> CursorLoader mCursorLoader = new CursorLoader(mContext, ContentLoaderConstant.CONTENT_URI, ContentLoaderConstant.PROJECTION, null, null, null);<br /> mCursorLoader.setUpdateThrottle(5000);<br /> return mCursorLoader;<br /> }<br /> /**<br /> * 加载完成刷新界面显示。<br /> */<br /> @Override<br /> public void onLoadFinished(Loader<Cursor> loader, Cursor mCursor) {<br /> mSimpleCursorAdapter.swapCursor(mCursor);<br /> }<br /> /**<br /> * 加载完成重置界面显示。<br /> */<br /> @Override<br /> public void onLoaderReset(Loader<Cursor> loader) {<br /> mSimpleCursorAdapter.swapCursor(null);<br /> }</p> <p>} 

    （4）ContentProvider代码：package com.focus.content.loader;<br /> import java.util.HashMap;<br /> import android.content.ContentProvider;<br /> import android.content.ContentUris;<br /> import android.content.ContentValues;<br /> import android.content.UriMatcher;<br /> import android.database.Cursor;<br /> import android.database.DatabaseUtils;<br /> import android.database.SQLException;<br /> import android.database.sqlite.SQLiteDatabase;<br /> import android.database.sqlite.SQLiteQueryBuilder;<br /> import android.net.Uri;<br /> import android.text.TextUtils;<br /> /**<br /> *<br /> * ContentProvider实现，对数据库执行增，删，改，查操作。<br /> *<br /> * @author 马英才。<br /> *<br /> */<br /> public class ContentLoaderProvider extends ContentProvider {<br /> private final UriMatcher mUriMatcher;</p> <p> private final HashMap<String, String> mNotesProjectionMap;</p> <p> private DataBaseHelper mDataBaseOpenHelper;</p> <p> public ContentLoaderProvider() {<br /> mUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);<br /> mUriMatcher.addURI(ContentLoaderConstant.AUTHORITY, ContentLoaderConstant.TABLE_NAME, ContentLoaderConstant.FOCUS);<br /> mUriMatcher.addURI(ContentLoaderConstant.AUTHORITY, ContentLoaderConstant.TABLE_NAME + "/#", ContentLoaderConstant.FOCUS_ID);<br /> mNotesProjectionMap = new HashMap<String, String>();<br /> mNotesProjectionMap.put(ContentLoaderConstant._ID, ContentLoaderConstant._ID);<br /> mNotesProjectionMap.put(ContentLoaderConstant.COLUMN_NAME_DATA, ContentLoaderConstant.COLUMN_NAME_DATA);<br /> }<br /> @Override<br /> public boolean onCreate() {<br /> mDataBaseOpenHelper = new DataBaseHelper(getContext());<br /> return true;<br /> }<br /> /**<br /> * 向数据库中插入数据，并notifyChange告诉CursorLoader加载数据，如果不调用notifyChange那么CursorLoader不会来加载数据<br /> * 即使给CursorLoader设置的取数据的间隔时间，它也不会来取数据，除非调用了notifyChange他才会来取。<br /> */<br /> @Override<br /> public Uri insert(Uri uri, ContentValues initialValues) {<br /> if (mUriMatcher.match(uri) != ContentLoaderConstant.FOCUS) {<br /> throw new IllegalArgumentException("Unknown URI " + uri);<br /> }<br /> ContentValues values;<br /> if (initialValues != null) {<br /> values = new ContentValues(initialValues);<br /> } else {<br /> values = new ContentValues();<br /> }<br /> if (values.containsKey(ContentLoaderConstant.COLUMN_NAME_DATA) == false) {<br /> values.put(ContentLoaderConstant.COLUMN_NAME_DATA, "");<br /> }<br /> SQLiteDatabase db = mDataBaseOpenHelper.getWritableDatabase();<br /> long rowId = db.insert(ContentLoaderConstant.TABLE_NAME, null, values);<br /> if (rowId > 0) {<br /> Uri noteUri = ContentUris.withAppendedId(ContentLoaderConstant.CONTENT_ID_URI_BASE, rowId);<br /> getContext().getContentResolver().notifyChange(noteUri, null);<br /> return noteUri;<br /> }<br /> throw new SQLException("Failed to insert row into " + uri);<br /> }<br /> /**<br /> * 从数据库中删除数据，并notifyChange告诉CursorLoader加载数据。<br /> */<br /> @Override<br /> public int delete(Uri uri, String where, String[] whereArgs) {<br /> SQLiteDatabase db = mDataBaseOpenHelper.getWritableDatabase();<br /> String finalWhere;<br /> int count;<br /> switch (mUriMatcher.match(uri)) {<br /> case ContentLoaderConstant.FOCUS:<br /> count = db.delete(ContentLoaderConstant.TABLE_NAME, where, whereArgs);<br /> break;<br /> case ContentLoaderConstant.FOCUS_ID:<br /> finalWhere = DatabaseUtils.concatenateWhere(ContentLoaderConstant._ID + " = " + ContentUris.parseId(uri), where);<br /> count = db.delete(ContentLoaderConstant.TABLE_NAME, finalWhere, whereArgs);<br /> break;<br /> default:<br /> throw new IllegalArgumentException("Unknown URI " + uri);<br /> }<br /> getContext().getContentResolver().notifyChange(uri, null);<br /> return count;<br /> }<br /> /**<br /> * 更新数据库中的数据，并notifyChange告诉CursorLoader加载数据。<br /> */<br /> @Override<br /> public int update(Uri uri, ContentValues values, String where, String[] whereArgs) {<br /> SQLiteDatabase db = mDataBaseOpenHelper.getWritableDatabase();<br /> int count;<br /> String finalWhere;<br /> switch (mUriMatcher.match(uri)) {<br /> case ContentLoaderConstant.FOCUS:<br /> count = db.update(ContentLoaderConstant.TABLE_NAME, values, where, whereArgs);<br /> break;<br /> case ContentLoaderConstant.FOCUS_ID:<br /> finalWhere = DatabaseUtils.concatenateWhere(ContentLoaderConstant._ID + " = " + ContentUris.parseId(uri), where);<br /> count = db.update(ContentLoaderConstant.TABLE_NAME, values, finalWhere, whereArgs);<br /> break;<br /> default:<br /> throw new IllegalArgumentException("Unknown URI " + uri);<br /> }<br /> getContext().getContentResolver().notifyChange(uri, null);<br /> return count;<br /> }<br /> /**<br /> * 从数据库中查询数据。<br /> */<br /> @Override<br /> public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {<br /> SQLiteQueryBuilder qb = new SQLiteQueryBuilder();</p> <p> qb.setTables(ContentLoaderConstant.TABLE_NAME);<br /> switch (mUriMatcher.match(uri)) {<br /> case ContentLoaderConstant.FOCUS :<br /> qb.setProjectionMap(mNotesProjectionMap);<br /> break;<br /> case ContentLoaderConstant.FOCUS_ID :<br /> qb.setProjectionMap(mNotesProjectionMap);<br /> qb.appendWhere(ContentLoaderConstant._ID + "=?");<br /> selectionArgs = DatabaseUtils.appendSelectionArgs(selectionArgs, new String[] {uri.getLastPathSegment()});<br /> break;<br /> default:<br /> throw new IllegalArgumentException("Unknown URI " + uri);<br /> }<br /> if (TextUtils.isEmpty(sortOrder)) {<br /> sortOrder = ContentLoaderConstant.DEFAULT_SORT_ORDER;<br /> }<br /> SQLiteDatabase db = mDataBaseOpenHelper.getReadableDatabase();<br /> Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, sortOrder);<br /> c.setNotificationUri(getContext().getContentResolver(), uri);</p> <p> return c;<br /> }<br /> @Override<br /> public String getType(Uri uri) {<br /> switch (mUriMatcher.match(uri)) {<br /> case ContentLoaderConstant.FOCUS :<br /> return ContentLoaderConstant.CONTENT_TYPE;<br /> case ContentLoaderConstant.FOCUS_ID :<br /> return ContentLoaderConstant.CONTENT_ITEM_TYPE;<br /> default :<br /> throw new IllegalArgumentException("Unknown URI " + uri);<br /> }<br /> }<br /> } 

    （5）DataBaseHelper代码：package com.focus.content.loader;<br /> import android.content.Context;<br /> import android.database.sqlite.SQLiteDatabase;<br /> import android.database.sqlite.SQLiteOpenHelper;<br /> public class DataBaseHelper extends SQLiteOpenHelper {<br /> public DataBaseHelper(Context context) {<br /> super(context, ContentLoaderConstant.DATABASE_NAME, null, ContentLoaderConstant.DATABASE_VERSION);<br /> }</p> <p> @Override<br /> public void onCreate(SQLiteDatabase mSQLiteDatabase) {<br /> mSQLiteDatabase.execSQL("CREATE TABLE "<br /> + ContentLoaderConstant.TABLE_NAME<br /> + " ("<br /> + ContentLoaderConstant._ID<br /> + " INTEGER PRIMARY KEY,"<br /> + ContentLoaderConstant.COLUMN_NAME_DATA<br /> + " TEXT"<br /> + ");");<br /> }<br /> @Override<br /> public void onUpgrade(SQLiteDatabase mSQLiteDatabase, int oldVersion, int newVersion) {<br /> mSQLiteDatabase.execSQL("DROP TABLE IF EXISTS notes");<br /> onCreate(mSQLiteDatabase);<br /> }<br /> } 

    （6）常量文件代码：package com.focus.content.loader;<br /> import android.net.Uri;<br /> public class ContentLoaderConstant {</p> <p> private ContentLoaderConstant() { </p> <p> }<br /> public static final String DATABASE_NAME = "mayingcai.db";</p> <p> public static final int DATABASE_VERSION = 1;<br /> public static final String AUTHORITY = "com.focus.content.loader.Focus";</p> <p> public static final String TABLE_NAME = "focus";<br /> public static final String _ID = "_id";<br /> public static final String COLUMN_NAME_DATA = "content";</p> <p> public static final int FOCUS = 1;</p> <p> public static final int FOCUS_ID = 2;<br /> public static final String DEFAULT_SORT_ORDER = "content COLLATE LOCALIZED ASC";<br /> public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.focus.content.loader.Focus";<br /> public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.focus.content.loader.Focus";</p> <p> public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/" + TABLE_NAME);<br /> public static final Uri CONTENT_ID_URI_BASE = Uri.parse("content://" + AUTHORITY + "/"+ TABLE_NAME +"/");<br /> public static final String[] PROJECTION = new String[] {<br /> _ID,<br /> COLUMN_NAME_DATA,<br /> };</p> <p>} 

    （7）AndroidManifest.xml配置文件：<?xml version="1.0" encoding="utf-8"?><br /> <manifest xmlns:android = "http://schemas.android.com/apk/res/android"<br /> package = "com.focus.content.loader"<br /> android:versionCode = "1"<br /> android:versionName = "1.0"<br /> ></p> <p> <application android:icon = "@drawable/icon" android:label = "@string/app_name"></p> <p> <activity android:name = ".ContentLoaderActivity"<br /> android:label = "@string/app_name"<br /> ><br /> <intent-filter><br /> <action android:name = "android.intent.action.MAIN" /><br /> <category android:name = "android.intent.category.LAUNCHER" /><br /> </intent-filter><br /> </activity><br /> <provider<br /> android:name = ".ContentLoaderProvider"<br /> android:authorities = "com.focus.content.loader.Focus"<br /> /><br /> </application></p> <p> <uses-sdk android:minSdkVersion = "11" /></p> <p></manifest>