HoneyComb3.0技術系列之ContentLoader

1. 概念：

 

    在HoneyComb3.0中提出了新的異步數據加載特性(ContentLoader)，它可以異步的從後臺獲取數據並更新UI界面。CursorLoader類是專門爲此

 

    特性設計的，他允許程序通過ContentProvider異步的從數據中讀取數據，並將獲取的數據顯示到UI界面中。

 

2. 效果圖：

 

    （1）主操作界面，在Action|Bar中存在兩個"快捷按鈕"，如下圖：

            

 

    （2）單擊"加載按鈕"後從數據庫中動態的加載數據（當前數據庫只添加了一條數據），如下圖：

            

    （3）間隔5秒後繼續從數據庫中讀取數據（數據庫被動態的添加了數據，並調用ContentResovler的notifiyChange()方法，該方法不調5秒後不

 

            會加載數據）：

           

3. 功能實現：

 

    （1）主Activity代碼：package com.focus.content.loader; import android.app.Activity; import android.app.FragmentManager; import android.os.Bundle; /** * * ContentLoader實例的入口Activity類。 * * @author 馬英才 * */ public class ContentLoaderActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); /** * 獲取FragmentManager實例。 */ FragmentManager mFragmentManager = getFragmentManager(); if (mFragmentManager.findFragmentById(android.R.id.content) == null) { /** * 創建ContentLoaderFragment,這是一個ListFragment,用於顯示結果。 */ ContentLoaderFragment mContentLoaderFragment = new ContentLoaderFragment(); /** * 通過FragmentManager向Activity中添加Fragment。 */ mFragmentManager.beginTransaction().add(android.R.id.content, mContentLoaderFragment).commit(); } } }

 

    （2）查詢結果顯示器，ListFragment代碼：package com.focus.content.loader; import android.app.ListFragment; import android.content.ContentResolver; import android.content.ContentValues; import android.os.AsyncTask; import android.os.Bundle; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.widget.SimpleCursorAdapter; /** * * 顯示從數據庫中查詢出的內容的Fragment,它是ListFragment,即：Fragment中包含一個ListView組件。 * * @author 馬英才 * */ public class ContentLoaderFragment extends ListFragment { static final int POPULATE_ID = Menu.FIRST; static final int CLEAR_ID = Menu.FIRST+1; private SimpleCursorAdapter mSimpleCursorAdapter; private AsyncTask<Void, Void, Void> mPopulatingTask; @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); setHasOptionsMenu(true); /** * 渲染Adapter,即：給ListFragment中的ListView設置的Adapter實現。 */ mSimpleCursorAdapter = new SimpleCursorAdapter ( getActivity(), android.R.layout.simple_list_item_1, null, new String[] { ContentLoaderConstant.COLUMN_NAME_DATA }, new int[] { android.R.id.text1 }, 0 ); /** * 給ListFragment中的ListView組件設置Adapter實現。 */ setListAdapter(mSimpleCursorAdapter); /** * 通過LoaderManager初始化ContentLoader,initLoader()方法的等三個參數是LoaderCallbacks實現， * 在Callbacks實現中創建ContentLoader實例，並設置多長時間通過ContentLoader去異步的加載數據，並刷新界面顯示。 */ getLoaderManager().initLoader(0, null, new ContentLoaderCallBack(getActivity(), mSimpleCursorAdapter)); } /** * 向ActionBar中添加"快捷按鈕"。 */ @Override public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) { menu.add(Menu.NONE, POPULATE_ID, 0, "Populate Letter").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM); menu.add(Menu.NONE, CLEAR_ID, 0, "Clear").setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM); } /** * 單擊ActionBar中添加"快捷按鈕"觸發相應事件。 */ @Override public boolean onOptionsItemSelected(MenuItem item) { final ContentResolver cr = getActivity().getContentResolver(); switch (item.getItemId()) { case POPULATE_ID : if (mPopulatingTask != null) { mPopulatingTask.cancel(false); } /** * 異步的通過ContentProvider向數據庫中添加數據。 */ mPopulatingTask = new AsyncTask<Void, Void, Void>() { @Override protected Void doInBackground(Void... params) { for (char c = 'A'; c <= 'K'; c++) { if (isCancelled()) { break; } StringBuilder builder = new StringBuilder("Data "); builder.append(c); ContentValues values = new ContentValues(); values.put(ContentLoaderConstant.COLUMN_NAME_DATA, builder.toString()); cr.insert(ContentLoaderConstant.CONTENT_URI, values); try { Thread.sleep(1000); } catch (InterruptedException e) { } } return null; } }; mPopulatingTask.execute((Void [])null); return true; case CLEAR_ID: if (mPopulatingTask != null) { mPopulatingTask.cancel(false); mPopulatingTask = null; } /** * 異步的通過ContentProvider清除數據庫中的數據。 */ AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() { @Override protected Void doInBackground(Void... params) { cr.delete(ContentLoaderConstant.CONTENT_URI, null, null); return null; } }; task.execute((Void[])null); return true; default: return super.onOptionsItemSelected(item); } } } 

 

    （3）ContentLoader回調方法：package com.focus.content.loader; import android.app.LoaderManager; import android.content.Context; import android.content.CursorLoader; import android.content.Loader; import android.database.Cursor; import android.os.Bundle; import android.widget.SimpleCursorAdapter; /** * * LoaderCallbacks實現，創建CursorLoader,根據設置的更新時間，異步的從後臺數據庫搜索數據，並通過Adapter更新顯示列表。 * * @author 馬英才 * */ public class ContentLoaderCallBack implements LoaderManager.LoaderCallbacks<Cursor> { private Context mContext; private SimpleCursorAdapter mSimpleCursorAdapter; public ContentLoaderCallBack (Context mContext, SimpleCursorAdapter mSimpleCursorAdapter) { this.mContext = mContext; this.mSimpleCursorAdapter = mSimpleCursorAdapter; } /** * 創建CursorLoader(異步數據加載器)，並設置更新時間，這個Loader會根據更新時間從ContentProvider中加載數據。 */ @Override public Loader<Cursor> onCreateLoader(int id, Bundle args) { CursorLoader mCursorLoader = new CursorLoader(mContext, ContentLoaderConstant.CONTENT_URI, ContentLoaderConstant.PROJECTION, null, null, null); mCursorLoader.setUpdateThrottle(5000); return mCursorLoader; } /** * 加載完成刷新界面顯示。 */ @Override public void onLoadFinished(Loader<Cursor> loader, Cursor mCursor) { mSimpleCursorAdapter.swapCursor(mCursor); } /** * 加載完成重置界面顯示。 */ @Override public void onLoaderReset(Loader<Cursor> loader) { mSimpleCursorAdapter.swapCursor(null); } } 

 

    （4）ContentProvider代碼：package com.focus.content.loader; import java.util.HashMap; import android.content.ContentProvider; import android.content.ContentUris; import android.content.ContentValues; import android.content.UriMatcher; import android.database.Cursor; import android.database.DatabaseUtils; import android.database.SQLException; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteQueryBuilder; import android.net.Uri; import android.text.TextUtils; /** * * ContentProvider實現，對數據庫執行增，刪，改，查操作。 * * @author 馬英才。 * */ public class ContentLoaderProvider extends ContentProvider { private final UriMatcher mUriMatcher; private final HashMap<String, String> mNotesProjectionMap; private DataBaseHelper mDataBaseOpenHelper; public ContentLoaderProvider() { mUriMatcher = new UriMatcher(UriMatcher.NO_MATCH); mUriMatcher.addURI(ContentLoaderConstant.AUTHORITY, ContentLoaderConstant.TABLE_NAME, ContentLoaderConstant.FOCUS); mUriMatcher.addURI(ContentLoaderConstant.AUTHORITY, ContentLoaderConstant.TABLE_NAME + "/#", ContentLoaderConstant.FOCUS_ID); mNotesProjectionMap = new HashMap<String, String>(); mNotesProjectionMap.put(ContentLoaderConstant._ID, ContentLoaderConstant._ID); mNotesProjectionMap.put(ContentLoaderConstant.COLUMN_NAME_DATA, ContentLoaderConstant.COLUMN_NAME_DATA); } @Override public boolean onCreate() { mDataBaseOpenHelper = new DataBaseHelper(getContext()); return true; } /** * 向數據庫中插入數據，並notifyChange告訴CursorLoader加載數據，如果不調用notifyChange那麼CursorLoader不會來加載數據 * 即使給CursorLoader設置的取數據的間隔時間，它也不會來取數據，除非調用了notifyChange他纔會來取。 */ @Override public Uri insert(Uri uri, ContentValues initialValues) { if (mUriMatcher.match(uri) != ContentLoaderConstant.FOCUS) { throw new IllegalArgumentException("Unknown URI " + uri); } ContentValues values; if (initialValues != null) { values = new ContentValues(initialValues); } else { values = new ContentValues(); } if (values.containsKey(ContentLoaderConstant.COLUMN_NAME_DATA) == false) { values.put(ContentLoaderConstant.COLUMN_NAME_DATA, ""); } SQLiteDatabase db = mDataBaseOpenHelper.getWritableDatabase(); long rowId = db.insert(ContentLoaderConstant.TABLE_NAME, null, values); if (rowId > 0) { Uri noteUri = ContentUris.withAppendedId(ContentLoaderConstant.CONTENT_ID_URI_BASE, rowId); getContext().getContentResolver().notifyChange(noteUri, null); return noteUri; } throw new SQLException("Failed to insert row into " + uri); } /** * 從數據庫中刪除數據，並notifyChange告訴CursorLoader加載數據。 */ @Override public int delete(Uri uri, String where, String[] whereArgs) { SQLiteDatabase db = mDataBaseOpenHelper.getWritableDatabase(); String finalWhere; int count; switch (mUriMatcher.match(uri)) { case ContentLoaderConstant.FOCUS: count = db.delete(ContentLoaderConstant.TABLE_NAME, where, whereArgs); break; case ContentLoaderConstant.FOCUS_ID: finalWhere = DatabaseUtils.concatenateWhere(ContentLoaderConstant._ID + " = " + ContentUris.parseId(uri), where); count = db.delete(ContentLoaderConstant.TABLE_NAME, finalWhere, whereArgs); break; default: throw new IllegalArgumentException("Unknown URI " + uri); } getContext().getContentResolver().notifyChange(uri, null); return count; } /** * 更新數據庫中的數據，並notifyChange告訴CursorLoader加載數據。 */ @Override public int update(Uri uri, ContentValues values, String where, String[] whereArgs) { SQLiteDatabase db = mDataBaseOpenHelper.getWritableDatabase(); int count; String finalWhere; switch (mUriMatcher.match(uri)) { case ContentLoaderConstant.FOCUS: count = db.update(ContentLoaderConstant.TABLE_NAME, values, where, whereArgs); break; case ContentLoaderConstant.FOCUS_ID: finalWhere = DatabaseUtils.concatenateWhere(ContentLoaderConstant._ID + " = " + ContentUris.parseId(uri), where); count = db.update(ContentLoaderConstant.TABLE_NAME, values, finalWhere, whereArgs); break; default: throw new IllegalArgumentException("Unknown URI " + uri); } getContext().getContentResolver().notifyChange(uri, null); return count; } /** * 從數據庫中查詢數據。 */ @Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { SQLiteQueryBuilder qb = new SQLiteQueryBuilder(); qb.setTables(ContentLoaderConstant.TABLE_NAME); switch (mUriMatcher.match(uri)) { case ContentLoaderConstant.FOCUS : qb.setProjectionMap(mNotesProjectionMap); break; case ContentLoaderConstant.FOCUS_ID : qb.setProjectionMap(mNotesProjectionMap); qb.appendWhere(ContentLoaderConstant._ID + "=?"); selectionArgs = DatabaseUtils.appendSelectionArgs(selectionArgs, new String[] {uri.getLastPathSegment()}); break; default: throw new IllegalArgumentException("Unknown URI " + uri); } if (TextUtils.isEmpty(sortOrder)) { sortOrder = ContentLoaderConstant.DEFAULT_SORT_ORDER; } SQLiteDatabase db = mDataBaseOpenHelper.getReadableDatabase(); Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, sortOrder); c.setNotificationUri(getContext().getContentResolver(), uri); return c; } @Override public String getType(Uri uri) { switch (mUriMatcher.match(uri)) { case ContentLoaderConstant.FOCUS : return ContentLoaderConstant.CONTENT_TYPE; case ContentLoaderConstant.FOCUS_ID : return ContentLoaderConstant.CONTENT_ITEM_TYPE; default : throw new IllegalArgumentException("Unknown URI " + uri); } } } 

 

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

 

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

 

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