Android开发教程之ContentProvider数据存储
一、ContentProvider保存数据介绍
一个程序可以通过实现一个ContentProvider的抽象接口将自己的数据完全暴露出去,而且ContentProvider是以类似数据库中表的方式将数据暴露的。那么外界获取其提供的数据,也就应该与从数据库中获取数据的操作基本一样,只不过是采用URL来表示外界需要访问的“数据库”。
ContentProvider提供了一种多应用间数据共享的方式。
ContentProvider是个实现了一组用于提供其他应用程序存取数据的标准方法的类。应用程序可以在ContentProvider中执行如下操作:查询数据、修改数据、添加数据、删除数据。
标准的ContentProvider:Android提供了一些已经在系统中实现的标准ContentProvider,比如联系人信息,图片库等等,可以用这些ContentProvider来访问设备上存储的联系人信息、图片等等。
在ContentProvider中使用的查询字符串有别于标准的SQL查询,很多诸如select、add、delete、modify等操作都使用一种特殊的URL进行,这种URL由3部分组成,“content://”,代表数据的路径和一个可选的表示数据的ID。
content://media/internal/images这个URL将返回设备上存储的所有图片
content://contacts/people/这个URL将返回设备上的所有联系人信息
content://contacts/people/45这个URL返回单个结果(联系人信息中ID为45的联系人记录)
如果想要存储字节型数据,比如位图文件等,那保存该数据的数据列其实是一个表示实际保存保存文件的URL字符串,客户端通过它来读取对应的文件数据,处理这种数据类型的ContentProvider需要实现一个名为_data的字段,_data字段列出了该文件在Android文件系统上的精确路径。这个字段不仅是供客户端使用,而且也可以供ContentResolver使用。客户端可以调用ContentResolver.openOutputStream()方法来处理该URL指向的文件资源,如果是ContentResolver本身的话,由于其持有的权限比客户端要高,所以它能直接访问该数据文件。
二、使用方法
大多数ContentProvider使用Android文件系统或者SQLite数据库来保持数据,但是也可以以任何方式来存储。本例用SQLite数据库来保持数据。
1.创建一个接口,定义了一个名为CONTENT_URL,并且是publicstaticfinal的Uri类型的类变量,必须为其指定一个唯一的字符串值,最好的方案是类的全称,和数据列的名称。
publicinterfaceIProivderMetaData{ publicstaticfinalStringAUTHORITY="com.zhangmiao.datastoragedemo"; publicstaticfinalStringDB_NAME="book.db"; publicstaticfinalintVERSION=1; publicinterfaceBookTableMetaDataextendsBaseColumns{ publicstaticfinalStringTABLE_NAME="book"; publicstaticfinalUriCONTENT_URI=Uri.parse("content://" +AUTHORITY+"/"+TABLE_NAME); publicstaticfinalStringBOOK_ID="_id"; publicstaticfinalStringBOOK_NAME="name"; publicstaticfinalStringBOOK_PUBLISHER="publisher"; publicstaticfinalStringSORT_ORDER="_iddesc"; publicstaticfinalStringCONTENT_LIST="vnd.android.cursor.dir/vnd.bookprovider.book"; publicstaticfinalStringCONTENT_ITEM="vnd.android.cursor.item/vnd.bookprovider.book"; } }
2.实现SQLiteOpenHelper
publicclassContentProviderDBHelperextendsSQLiteOpenHelperimplementsIProivderMetaData{ privatestaticfinalStringTAG="ContentProviderDBHelper"; publicContentProviderDBHelper(Contextcontext){ super(context,DB_NAME,null,VERSION); } @Override publicvoidonCreate(SQLiteDatabasedb){ ... } @Override publicvoidonUpgrade(SQLiteDatabasedb,intoldVersion,intnewVersion){ ... } }
3.创建一个继承了ContentProvider父类的类
publicclassContentProviderDBHelperextendsSQLiteOpenHelperimplementsIProivderMetaData{ publicContentProviderDBHelper(Contextcontext){ super(context,DB_NAME,null,VERSION); } @Override publicvoidonCreate(SQLiteDatabasedb){ ... } @Override publicvoidonUpgrade(SQLiteDatabasedb,intoldVersion,intnewVersion){ ... } }
4.在AndroidManifest.xml中使用标签来设置调用ContentProvider。
<provider android:authorities="com.zhangmiao.datastoragedemo" android:name=".BookContentProvider"/>
5.增加数据
mContentResolver=getContentResolver(); String[]bookNames=newString[]{"Chinese","Math","English","Sports"}; String[]bookPublishers=newString[]{"XinHua","GongXin","DianZi","YouDian"}; for(inti=0;i<bookNames.length;i++){ ContentValuesvalues=newContentValues(); values.put(IProivderMetaData.BookTableMetaData.BOOK_NAME,bookNames[i]); values.put(IProivderMetaData.BookTableMetaData.BOOK_PUBLISHER,bookPublishers[i]); mContentResolver.insert(IProivderMetaData.BookTableMetaData.CONTENT_URI,values); }
6.删除数据
StringbookId="1"; if(!"".equals(bookId)){ ContentValuesvalues1=newContentValues(); values1.put(IProivderMetaData.BookTableMetaData.BOOK_ID,bookId); mContentResolver.delete(Uri.withAppendedPath( IProivderMetaData.BookTableMetaData.CONTENT_URI, bookId), "_id=?", newString[]{bookId} ); }else{ mContentResolver.delete( IProivderMetaData.BookTableMetaData.CONTENT_URI, null, null ); }
7.查询数据
Cursorcursor=mContentResolver.query(IProivderMetaData.BookTableMetaData.CONTENT_URI, null,null,null,null); Stringtext=""; if(cursor!=null){ while(cursor.moveToNext()){ StringbookIdText= cursor.getString(cursor.getColumnIndex(IProivderMetaData.BookTableMetaData.BOOK_ID)); StringbookNameText= cursor.getString(cursor.getColumnIndex(IProivderMetaData.BookTableMetaData.BOOK_NAME)); StringbookPublisherText= cursor.getString(cursor.getColumnIndex(IProivderMetaData.BookTableMetaData.BOOK_PUBLISHER)); text+="id="+bookIdText+",name="+bookNameText+ ",publisher="+bookPublisherText+"\n"; } cursor.close(); mTableInfo.setText(text); }
8.更新数据
StringbookId1="2"; StringbookName="Art"; StringbookPublisher="TieDao"; ContentValuesvalues2=newContentValues(); values2.put(IProivderMetaData.BookTableMetaData.BOOK_NAME,bookName); values2.put(IProivderMetaData.BookTableMetaData.BOOK_PUBLISHER,bookPublisher); if("".equals(bookId1)){ mContentResolver.update(IProivderMetaData.BookTableMetaData.CONTENT_URI, values2,null,null); }else{ mContentResolver.update(Uri.withAppendedPath(IProivderMetaData.BookTableMetaData.CONTENT_URI,bookId1), values2,"_id=?",newString[]{bookId1} ); }
三、小案例
1.添加strings.xml文件
<stringname="content_provider">ContentProvider</string> <stringname="add_data">增加数据</string> <stringname="delete_data">删除数据</string> <stringname="update_data">更改数据</string> <stringname="query_data">查询数据</string>
2.修改activity_main.xml文件
<?xmlversion="1.0"encoding="utf-8"?> <android.support.design.widget.CoordinatorLayoutxmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true" tools:context="com.zhangmiao.datastoragedemo.MainActivity"> <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_horizontal" android:text="@string/content_provider"/> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginBottom="@dimen/fab_margin" android:layout_marginTop="@dimen/fab_margin" android:orientation="horizontal"> <Button android:id="@+id/provider_add" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="@string/add_data"/> <Button android:id="@+id/provider_delete" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="@string/delete_data"/> <Button android:id="@+id/provider_update" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="@string/update_data"/> <Button android:id="@+id/provider_query" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="@string/query_data"/> </LinearLayout> <TextView android:id="@+id/table_info" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="@string/app_name"/> </LinearLayout> </android.support.design.widget.CoordinatorLayout>
3.添加IProviderMetaData接口
packagecom.zhangmiao.datastoragedemo; importandroid.net.Uri; importandroid.provider.BaseColumns; /** *Createdbyzhangmiaoon2016/12/20. */ publicinterfaceIProviderMetaData{ publicstaticfinalStringAUTHORITY="com.zhangmiao.datastoragedemo"; publicstaticfinalStringDB_NAME="book.db"; publicstaticfinalintVERSION=1; publicinterfaceBookTableMetaDataextendsBaseColumns{ publicstaticfinalStringTABLE_NAME="book"; publicstaticfinalUriCONTENT_URI=Uri.parse("content://" +AUTHORITY+"/"+TABLE_NAME); publicstaticfinalStringBOOK_ID="_id"; publicstaticfinalStringBOOK_NAME="name"; publicstaticfinalStringBOOK_PUBLISHER="publisher"; publicstaticfinalStringSORT_ORDER="_iddesc"; publicstaticfinalStringCONTENT_LIST="vnd.android.cursor.dir/vnd.bookprovider.book"; publicstaticfinalStringCONTENT_ITEM="vnd.android.cursor.item/vnd.bookprovider.book"; } }
4.添加ContentProviderDBHelper类
packagecom.zhangmiao.datastoragedemo; importandroid.content.Context; importandroid.database.sqlite.SQLiteDatabase; importandroid.database.sqlite.SQLiteOpenHelper; importandroid.util.Log; /** *Createdbyzhangmiaoon2016/12/20. */ publicclassContentProviderDBHelperextendsSQLiteOpenHelperimplementsIProviderMetaData{ privatestaticfinalStringTAG="ContentProviderDBHelper"; publicContentProviderDBHelper(Contextcontext){ super(context,DB_NAME,null,VERSION); } @Override publicvoidonCreate(SQLiteDatabasedb){ StringTABLESQL="CREATETABLEIFNOTEXISTS" +BookTableMetaData.TABLE_NAME+"(" +BookTableMetaData.BOOK_ID+"INTEGERPRIMARYKEYAUTOINCREMENT," +BookTableMetaData.BOOK_NAME+"VARCHAR," +BookTableMetaData.BOOK_PUBLISHER+"VARCHAR)"; db.execSQL(TABLESQL); } @Override publicvoidonUpgrade(SQLiteDatabasedb,intoldVersion,intnewVersion){ Log.w(TAG,"Upgradingdatabasefromversion"+oldVersion+"to" +newVersion+",whichwilldestroyallolddata"); db.execSQL("DROPTABLEIFEXISTS"+DB_NAME); onCreate(db); } }
5.添加BookContentProvider类
packagecom.zhangmiao.datastoragedemo; importandroid.content.ContentProvider; importandroid.content.ContentUris; importandroid.content.ContentValues; importandroid.content.UriMatcher; importandroid.database.Cursor; importandroid.database.sqlite.SQLiteDatabase; importandroid.net.Uri; importandroid.support.annotation.Nullable; importandroid.util.Log; /** *Createdbyzhangmiaoon2016/12/21. */ publicclassBookContentProviderextendsContentProvider{ privatestaticfinalStringTAG="BookContentProvider"; privatestaticUriMatcheruriMatcher=null; privatestaticfinalintBOOKS=1; privatestaticfinalintBOOK=2; privateContentProviderDBHelperdbHelper; privateSQLiteDatabasedb; static{ uriMatcher=newUriMatcher(UriMatcher.NO_MATCH); uriMatcher.addURI(IProviderMetaData.AUTHORITY, IProviderMetaData.BookTableMetaData.TABLE_NAME,BOOKS); uriMatcher.addURI(IProviderMetaData.AUTHORITY, IProviderMetaData.BookTableMetaData.TABLE_NAME+"/#", BOOK); } @Override publicbooleanonCreate(){ dbHelper=newContentProviderDBHelper(getContext()); return(dbHelper==null)?false:true; } @Nullable @Override publicStringgetType(Uriuri){ switch(uriMatcher.match(uri)){ caseBOOKS: returnIProviderMetaData.BookTableMetaData.CONTENT_LIST; caseBOOK: returnIProviderMetaData.BookTableMetaData.CONTENT_ITEM; default: thrownewIllegalArgumentException("ThisisaunKnowUri" +uri.toString()); } } @Nullable @Override publicUriinsert(Uriuri,ContentValuesvalues){ switch(uriMatcher.match(uri)){ caseBOOKS: db=dbHelper.getWritableDatabase(); longrowId=db.insert( IProviderMetaData.BookTableMetaData.TABLE_NAME, IProviderMetaData.BookTableMetaData.BOOK_ID, values); UriinsertUri=Uri.withAppendedPath(uri,"/"+rowId); Log.i(TAG,"insertUri:"+insertUri.toString()); getContext().getContentResolver().notifyChange(uri,null); returninsertUri; caseBOOK: default: thrownewIllegalArgumentException("ThisisaunKnowUri" +uri.toString()); } } @Nullable @Override publicCursorquery(Uriuri,String[]projection,Stringselection,String[]selectionArgs,StringsortOrder){ db=dbHelper.getReadableDatabase(); switch(uriMatcher.match(uri)){ caseBOOKS: returndb.query(IProviderMetaData.BookTableMetaData.TABLE_NAME, projection,selection,selectionArgs,null,null, sortOrder); caseBOOK: longid=ContentUris.parseId(uri); Stringwhere="_id="+id; if(selection!=null&&!"".equals(selection)){ where=selection+"and"+where; } returndb.query(IProviderMetaData.BookTableMetaData.TABLE_NAME, projection,where,selectionArgs,null,null,sortOrder); default: thrownewIllegalArgumentException("ThisisaunKnowUri" +uri.toString()); } } @Override publicintdelete(Uriuri,Stringselection,String[]selectionArgs){ db=dbHelper.getWritableDatabase(); switch(uriMatcher.match(uri)){ caseBOOKS: returndb.delete(IProviderMetaData.BookTableMetaData.TABLE_NAME, selection,selectionArgs); caseBOOK: longid=ContentUris.parseId(uri); Stringwhere="_id="+id; if(selection!=null&&!"".equals(selection)){ where=selection+"and"+where; } returndb.delete(IProviderMetaData.BookTableMetaData.TABLE_NAME, selection,selectionArgs); default: thrownewIllegalArgumentException("ThisisaunKnowUri" +uri.toString()); } } @Override publicintupdate(Uriuri,ContentValuesvalues,Stringselection,String[]selectionArgs){ db=dbHelper.getWritableDatabase(); switch(uriMatcher.match(uri)){ caseBOOKS: returndb.update(IProviderMetaData.BookTableMetaData.TABLE_NAME, values,null,null); caseBOOK: longid=ContentUris.parseId(uri); Stringwhere="_id="+id; if(selection!=null&&!"".equals(selection)){ where=selection+"and"+where; } returndb.update(IProviderMetaData.BookTableMetaData.TABLE_NAME, values,selection,selectionArgs); default: thrownewIllegalArgumentException("ThisisaunKnowUri" +uri.toString()); } } }
6.修改AndroidManifest.xml文件
<provider android:authorities="com.zhangmiao.datastoragedemo" android:name=".BookContentProvider"/>
7.修改MainActivity
packagecom.zhangmiao.datastoragedemo; importandroid.content.ContentResolver; importandroid.content.ContentValues; importandroid.database.Cursor; importandroid.net.*; importandroid.os.Bundle; importandroid.support.v7.app.AppCompatActivity; importandroid.util.Log; importandroid.view.View; importandroid.widget.Button; importandroid.widget.TextView;importjava.util.ArrayList; importjava.util.List; publicclassMainActivityextendsAppCompatActivityimplementsView.OnClickListener{privateContentResolvermContentResolver; privateBookContentProvidermBookContentProvider;privateTextViewmTableInfo; @Override protectedvoidonCreate(BundlesavedInstanceState){ Log.v("MainActivity","onCreate"); super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); ButtoncpAdd=(Button)findViewById(R.id.provider_add); ButtoncpDelete=(Button)findViewById(R.id.provider_delete); ButtoncpUpdate=(Button)findViewById(R.id.provider_update); ButtoncpQuery=(Button)findViewById(R.id.provider_query); mTableInfo=(TextView)findViewById(R.id.table_info); cpAdd.setOnClickListener(this); cpDelete.setOnClickListener(this); cpQuery.setOnClickListener(this); cpUpdate.setOnClickListener(this); } @Override publicvoidonClick(Viewv){ switch(v.getId()){caseR.id.provider_add: mContentResolver=getContentResolver(); String[]bookNames=newString[]{"Chinese","Math","English","Sports"}; String[]bookPublishers=newString[]{"XinHua","GongXin","DianZi","YouDian"}; for(inti=0;i<bookNames.length;i++){ ContentValuesvalues=newContentValues(); values.put(IProviderMetaData.BookTableMetaData.BOOK_NAME,bookNames[i]); values.put(IProviderMetaData.BookTableMetaData.BOOK_PUBLISHER,bookPublishers[i]); mContentResolver.insert(IProviderMetaData.BookTableMetaData.CONTENT_URI,values); } break; caseR.id.provider_delete: StringbookId="1"; if(!"".equals(bookId)){ ContentValuesvalues1=newContentValues(); values1.put(IProviderMetaData.BookTableMetaData.BOOK_ID, bookId); mContentResolver.delete( Uri.withAppendedPath( IProviderMetaData.BookTableMetaData.CONTENT_URI, bookId ),"_id=?", newString[]{bookId} ); }else{ mContentResolver.delete( IProviderMetaData.BookTableMetaData.CONTENT_URI, null, null ); } break; caseR.id.provider_query: Cursorcursor=mContentResolver.query(IProviderMetaData.BookTableMetaData.CONTENT_URI,null,null,null,null); Stringtext=""; if(cursor!=null){ while(cursor.moveToNext()){ StringbookIdText= cursor.getString(cursor.getColumnIndex(IProviderMetaData.BookTableMetaData.BOOK_ID)); StringbookNameText= cursor.getString(cursor.getColumnIndex(IProviderMetaData.BookTableMetaData.BOOK_NAME)); StringbookPublisherText= cursor.getString(cursor.getColumnIndex(IProviderMetaData.BookTableMetaData.BOOK_PUBLISHER)); text+="id="+bookIdText+",name="+bookNameText+",publisher="+bookPublisherText+"\n"; } cursor.close(); mTableInfo.setText(text); } break; caseR.id.provider_update: StringbookId1="2"; StringbookName="Art"; StringbookPublisher="TieDao"; ContentValuesvalues2=newContentValues(); values2.put(IProviderMetaData.BookTableMetaData.BOOK_NAME, bookName); values2.put(IProviderMetaData.BookTableMetaData.BOOK_PUBLISHER, bookPublisher); if("".equals(bookId1)){ mContentResolver.update( IProviderMetaData.BookTableMetaData.CONTENT_URI, values2,null,null); }else{ mContentResolver.update( Uri.withAppendedPath( IProviderMetaData.BookTableMetaData.CONTENT_URI,bookId1), values2,"_id=?",newString[]{bookId1}); } break;default: Log.v("MainActivity","default"); break; } } }