ContentProvider实现数据共享
ContentProvider在android中的作用是对外共享数据，也就是说你可以通过ContentProvider把应用中的数据共享给其他应用访问，其他应用可以通过ContentProvider对你应用中的数据进行添删改查。关于数据共享，我们知道，通过设定文件的操作模式为Content.MODE_WORLD_READABLE或Context.MODE_WORLD_WRITEABLE同样也可以对外共享数据。那么，这里ContentProvider对外共享数据相对文件共享有什么样的优势了。是这样的，如果采用文件操作模式对外共享数据，数据的访问方式会因数据存储的方式而不同，导致数据的访问方式无法统一，如:采用xml文件对外共享数据，需要进行xml解析才能读取数据；采用sharepreferences共享数据，需要使用sharepreferences API读取数据。
使用ContentProvider对外共享数据的好处是统一了数据的访问方式。
当应用需要通过ContentProvider对外共享数据时，第一步需要继承ContentProvider并重写下面方法。
public class PersonContentProvider extends ContentProvider{
public boolean onCreate();
public Uri insert(Uri uri, String selection, String[] selectionArgs);
public int delete(Uri uri, String selection , String[] selectionArgs);
public int update(Uri uri, ContentValues, String selection, String[] selectionArgs);
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder);
public String getType(Uri uri);
}
第二步需要在AndroidManifest.xml使用
这里我给出一个对sqlite数据库实现ContentProvider对外共享数据的范例。
A应用:名称为db(主要代码)
package com.example.db;
import com.example.service.DbOpenHelper;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
public class PersonProvider extends ContentProvider {
private DbOpenHelper openHelper;
private static final UriMatcher MATCHER = new UriMatcher(UriMatcher.NO_MATCH);
private static final int PERSONS = 1;
private static final int PERSON = 2;
static{
MATCHER.addURI("com.example.providers.personprovider", "person", PERSONS);
//* 根据pesonid来删除记录
MATCHER.addURI("com.example.providers.personprovider", "person/#", PERSON);
}
@Override
public boolean onCreate() {
openHelper = new DbOpenHelper(this.getContext());
return false;
}
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteDatabase sqLiteDatabase = openHelper.getReadableDatabase();
switch (MATCHER.match(uri)) {
case 1:
return sqLiteDatabase.query("person", projection, selection, selectionArgs, null, null, sortOrder);
case 2:
long rowid = ContentUris.parseId(uri);
String where = "personid="+rowid;
if(selection != null && "".equals(selection.trim())){
where = selection+"and"+where;
}
return sqLiteDatabase.query("person", projection, where, selectionArgs, null, null, sortOrder);
}
return null;
}
@Override
public String getType(Uri uri) {
switch (MATCHER.match(uri)) {
case 1:
return "vnd.android.cursor.dir/person";
case 2:
return "vnd.android.cursor.item/person";
}
return null;
}
@Override
public Uri insert(Uri uri, ContentValues values) {
SQLiteDatabase sqLiteDatabase = openHelper.getWritableDatabase();
switch (MATCHER.match(uri)) {
case 1:
long rowid = sqLiteDatabase.insert("person", "name", values);
return ContentUris.withAppendedId(uri, rowid);
default:
break;
}
return null;
}
//* 删除特定personid行的记录
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
SQLiteDatabase sqLiteDatabase = openHelper.getWritableDatabase();
switch (MATCHER.match(uri)) {
case 1:
return sqLiteDatabase.delete("person", selection, selectionArgs);
case 2:
long rowid = ContentUris.parseId(uri);
String where = "personid="+rowid;
if(selection != null && "".equals(selection.trim())){
where = selection+"and"+where;
}
return sqLiteDatabase.delete("person", where, selectionArgs);
}
return 0;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
SQLiteDatabase sqLiteDatabase = openHelper.getWritableDatabase();
switch (MATCHER.match(uri)) {
case 1:
return sqLiteDatabase.update("person", values, selection, selectionArgs);
case 2:
long rowid = ContentUris.parseId(uri);
String where = "personid="+rowid;
if(selection != null && "".equals(selection.trim())){
where = selection+"and"+where;
}
return sqLiteDatabase.update("person", values, where, selectionArgs);
}
return 0;
}
}
UriMatcher类似一个文本过滤器，它是用来匹配Uri.
第一步对其进行初始化:
UriMatcher MATCHER = new UriMatcher(UriMatcher.NO_MATCH);第二步对其进行注册，附加Uri:
MATCHER.addURI("com.example.providers.personprovider", "person", PERSONS);
//* 根据pesonid来删除记录
MATCHER.addURI("com.example.providers.personprovider", "person/#", PERSON);"com.example.providers.personprovider"就是域名，通过他可以相对应的找到特定的ContentProvider
MATCHER.match(uri)会返回一个code,code就是第二步传入的第二个参数
long rowid = ContentUris.parseId(uri);会得到uri后边对应的id.
测试代码:
package com.example.other;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.test.AndroidTestCase;
public class AccessProvider extends AndroidTestCase {
public void testInsert(){
Uri uri = Uri.parse("content://com.example.providers.personprovider/person");
ContentResolver resolver = this.getContext().getContentResolver();
ContentValues values = new ContentValues();
values.put("name", "xiaohua");
values.put("phone", "12121212");
resolver.insert(uri, values);
}
public void testDelete(){
Uri uri = Uri.parse("content://com.example.providers.personprovider/person/2");
ContentResolver resolver = this.getContext().getContentResolver();
resolver.delete(uri, null, null);
}
public void testUpdate(){
Uri uri = Uri.parse("content://com.example.providers.personprovider/person/3");
ContentResolver resolver = this.getContext().getContentResolver();
ContentValues values = new ContentValues();
values.put("name", "hanfei");
values.put("phone", "00000000");
resolver.update(uri, values, null, null);
}
public void testQuery(){
Uri uri = Uri.parse("content://com.example.providers.personprovider/person");
ContentResolver resolver = this.getContext().getContentResolver();
Cursor cursor = resolver.query(uri, new String[]{"name","phone"}, null, null, null);
while(cursor.moveToNext()){
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
System.out.println("name="+name+" "+"phone="+phone);
}
}
}
下载地址:http://download.csdn.net/detail/tan313/8508063