android 四大重要的组件之ContentProvider

Android开发中四个重要的组件：

1、Activiyt

2、Broadcast Intent Receiver

3、Service

4、Content Provider

一个ContentProvider类实现了一组标准的方法接口，从而能够让其他的应用保存或读取此ContentProvider的各种数据类型。

下面列举一些常用的接口：

1、query(Uri uri,String[] projection,String selection,String[]selectionArgs,String sortOrder):通过Uri进行查询，返回一个Cursor.

2、insert(Uri uri,ContentValues values):将一组数据插入到Uri指定的地方。

3、update(Uri uri,ContentValues values,String where,String[]selectionArgs):更新Uri指定位置的数据。

4、delete（Uriuri,String where,String[] selectionArgs）:删除指定Uri并且符合一定条件的数据。

ContentResolver

外界程序通过ContentResolver接口可以访问ContentProvider提供的数据，在Activity当中通过getContentResolver（）可以得到当前应用ContentResolver实例。其提供的接口与ContentProvider提供的接口对应：

1、query(Uri uri,String[] projection,String selection,String[]selectionArgs,String sortOrder):通过Uri进行查询，返回一个Cursor.

2、insert(Uri uri,ContentValues values):将一组数据插入到Uri指定的地方。

3、update(Uri uri,ContentValues values,String where,String[]selectionArgs):更新Uri指定位置的数据。

4、delete（Uriuri,String where,String[] selectionArgs）:删除指定Uri并且符合一定条件的数据。

实例：

1.要为当前应用程序的私有数据定义URI，就需要专门定义个继承自ContentProvider的类，然后实现各个不同的操作所调用的方法。

1、PersonProvider

package cn.class3g.db;

import cn.class3g.service.DatabaseHelper;

importandroid.content.ContentProvider;

import android.content.ContentUris;

importandroid.content.ContentValues;

importandroid.content.UriMatcher;

importandroid.database.Cursor;

importandroid.database.sqlite.SQLiteDatabase;

import android.net.Uri;

public class PersonProvider extendsContentProvider {

privatestatic UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);

privatestatic final int PERSONS = 1;

privatestatic final int PERSON = 2;

privateDatabaseHelper dbHelper;

static{

matcher.addURI("cn.class3g.providers.personprovider", "person",PERSONS);

matcher.addURI("cn.class3g.providers.personprovider","person/#",

PERSON);

}

publicboolean onCreate() {

dbHelper= new DatabaseHelper(this.getContext());

returntrue;

}

//content://cn.itcast.provides.personprovider/person

public Uri insert(Uri uri, ContentValuesvalues) {

SQLiteDatabasedb = dbHelper.getWritableDatabase();

longrowId;

switch(matcher.match(uri)) {

casePERSONS: //向表中添加新纪录并返回其行号

rowId= db.insert("person", "personid", values);

returnContentUris.withAppendedId(uri, rowId);

default:

thrownew IllegalArgumentException("Unknow Uri:" + uri);

}

publicCursor query(Uri uri, String[] projection, String selection,

String[]selectionArgs, String sortOrder) {

SQLiteDatabasedb = dbHelper.getReadableDatabase();

switch(matcher.match(uri)) {

casePERSONS:

returndb.query("person", projection, selection, selectionArgs, null, null,sortOrder);

casePERSON:

longpersonid = ContentUris.parseId(uri);

Stringwhere = "personid="+ personid;

if(selection!=null&& !"".equals(selection)){

where= where + " and "+ selection;

}

returndb.query("person", projection, where, selectionArgs, null, null,sortOrder);

default:

thrownew IllegalArgumentException("Unknown Uri:"+ uri);

}

//content://cn.itcast.provides.personprovider/person 更新表中的所有记录

//content://cn.itcast.provides.personprovider/person/10 更新表中指定id的记录

publicint update(Uri uri, ContentValues values, String selection,

String[]selectionArgs) {

SQLiteDatabasedb = dbHelper.getWritableDatabase();

intnum;

switch(matcher.match(uri)){

casePERSONS: //更新指定记录

num= db.update("person", values, selection, selectionArgs);

break;

casePERSON:

longpersonid = ContentUris.parseId(uri);

Stringwhere = "personid=" + personid;

if(selection!= null){

where+= " and " + selection;

}

num= db.update("person", values, where, selectionArgs);

break;

default:

thrownew IllegalArgumentException("Unknow Uri"+uri);

}

returnnum;

}

publicint delete(Uri uri, String selection, String[] selectionArgs) {

SQLiteDatabasedb = dbHelper.getWritableDatabase();

intnum = 0;

switch(matcher.match(uri)) {

casePERSONS:

num= db.delete("person", selection, selectionArgs);

break;

casePERSON:

longpersonid = ContentUris.parseId(uri);

Stringwhere = "personid="+ personid;

if(selection!=null&& !"".equals(selection)){

where= where + " and "+ selection;

}

num= db.delete("person", where, selectionArgs);

break;

default:

thrownew IllegalArgumentException("Unknown Uri:"+ uri);

}

returnnum;

}

publicString getType(Uri uri) {

switch(matcher.match(uri)) {

casePERSONS:

return"vnd.android.cursor.dir/person";

casePERSON:

return"vnd.android.cursor.item/person";

default:

thrownew IllegalArgumentException("Unknown Uri:"+ uri);

}

2.在AndroidManifest中配置

<provider

android:authorities="cn.class3g.providers.personprovider"

android:name="PersonProvider" >

</provider>

3.建立测试工程编写测试代码

public class AccessContentProviderTestextends AndroidTestCase {

publicvoid testSave() throws Throwable{

ContentResolverresolver = this.getContext().getContentResolver();

UriinsertUri = Uri.parse("content://cn.class3g.providers.personprovider/person");

ContentValuesvalues = new ContentValues();

values.put("name","laozhang");

values.put("age","50");

Uriuri = resolver.insert(insertUri, values);

Log.i("TAG",uri.toString());

}

publicvoid testQuery() throws Throwable{

ContentResolverresolver = this.getContext().getContentResolver();

Uriuri = Uri.parse("content://cn.class3g.providers.personprovider/person");

Cursorcursor = resolver.query(uri, null, null, null, "personid asc");

while(cursor.moveToNext()){

intpersonid = cursor.getInt(cursor.getColumnIndex("personid"));

Stringname = cursor.getString(cursor.getColumnIndex("name"));

Log.i("TAG","personid="+ personid + ",name="+ name);

}

cursor.close();

}

publicvoid testUpdate() throws Throwable{

ContentResolvercontentResolver =

this.getContext().getContentResolver();

UriupdateUri = Uri.parse("content://cn.class3g.providers.personprovider/person/5");

ContentValuesvalues = new ContentValues();

values.put("name","袁世凯");

contentResolver.update(updateUri,values, null, null);

}

publicvoid testDelete() throws Throwable{

ContentResolvercontentResolver = this.getContext().getContentResolver();

Uriuri = Uri.parse("content://cn.class3g.providers.personprovider/person/5");

contentResolver.delete(uri,null, null);

}

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