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;
}
}
}