ContentProvider内容提供者(一)
| 作为四大组件之一的ContentProvider,其作用是对外共享数据，相对文件和数据库存储来说，它的好处是统一了数据访问方式。 先来看看基本的介绍： Class Overview Content providers are one of the primary building blocks of Android applications, providing content to applications. They encapsulate data and provide it to applications through the single When a request is made via a The primary methods that need to be implemented are:
Data access methods (such as Requests to 这里有个Uri匹配类：UriMatcher，它的基本介绍如下： Class OverviewUtility class to aid in matching URIs in content providers. To use this class, build up a tree of private static final int PEOPLE = 1; private static final int PEOPLE_ID = 2; private static final int PEOPLE_PHONES = 3; private static final int PEOPLE_PHONES_ID = 4; private static final int PEOPLE_CONTACTMETHODS = 7; private static final int PEOPLE_CONTACTMETHODS_ID = 8; private static final int DELETED_PEOPLE = 20; private static final int PHONES = 9; private static final int PHONES_ID = 10; private static final int PHONES_FILTER = 14; private static final int CONTACTMETHODS = 18; private static final int CONTACTMETHODS_ID = 19; private static final int CALLS = 11; private static final int CALLS_ID = 12; private static final int CALLS_FILTER = 15; private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH); static { sURIMatcher.addURI("contacts", "people", PEOPLE); sURIMatcher.addURI("contacts", "people/#", PEOPLE_ID); sURIMatcher.addURI("contacts", "people/#/phones", PEOPLE_PHONES); sURIMatcher.addURI("contacts", "people/#/phones/#", PEOPLE_PHONES_ID); sURIMatcher.addURI("contacts", "people/#/contact_methods", PEOPLE_CONTACTMETHODS); sURIMatcher.addURI("contacts", "people/#/contact_methods/#", PEOPLE_CONTACTMETHODS_ID); sURIMatcher.addURI("contacts", "deleted_people", DELETED_PEOPLE); sURIMatcher.addURI("contacts", "phones", PHONES); sURIMatcher.addURI("contacts", "phones/filter/*", PHONES_FILTER); sURIMatcher.addURI("contacts", "phones/#", PHONES_ID); sURIMatcher.addURI("contacts", "contact_methods", CONTACTMETHODS); sURIMatcher.addURI("contacts", "contact_methods/#", CONTACTMETHODS_ID); sURIMatcher.addURI("call_log", "calls", CALLS); sURIMatcher.addURI("call_log", "calls/filter/*", CALLS_FILTER); sURIMatcher.addURI("call_log", "calls/#", CALLS_ID); } Then when you need to match against a URI, call public String getType(Uri url) { int match = sURIMatcher.match(url); switch (match) { case PEOPLE: return "vnd.android.cursor.dir/person"; case PEOPLE_ID: return "vnd.android.cursor.item/person"; ... snip ... return "vnd.android.cursor.dir/snail-mail"; case PEOPLE_ADDRESS_ID: return "vnd.android.cursor.item/snail-mail"; default: return null; } } instead of: public String getType(Uri url) { List pathSegments = url.getPathSegments(); if (pathSegments.size() >= 2) { if ("people".equals(pathSegments.get(1))) { if (pathSegments.size() == 2) { return "vnd.android.cursor.dir/person"; } else if (pathSegments.size() == 3) { return "vnd.android.cursor.item/person"; ... snip ... return "vnd.android.cursor.dir/snail-mail"; } else if (pathSegments.size() == 3) { return "vnd.android.cursor.item/snail-mail"; } } } return null; }
其他应用可以通过ContentResolver的实例来访问内容提供者的数据，它的基本介绍：
Class OverviewThis class provides applications access to the content model. 通过它的insert()、delete()、update()、query()来对内容提供者数据进行添删改查操作。
下面通过一个实例来看一下如何使用ContentProvider进行数据共享 我们需要建立两个project：Android_ContentProvider和Android_ContentProvider_Test，分别作为内容提供者和对数据访问者。 在前者中，我们定义一个自己的PersonProvider,提供对person表的数据操作，在后者中，我们通过Junit Test 的test方法来完成数据操作测试。 Android_ContentProvider的目录结构：
这里的布局文件和Ui等没有意义，我们重点看一下DBOpenHelper和PersonProvider两个类，分别是数据库工具类和自定义内容提供者， DBOpenHelper.java代码如下：
package com.wujay.provider.service;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class DBOpenHelper extends SQLiteOpenHelper{
/**
* 构造函数
* @param context
*/
public DBOpenHelper(Context context) {
super(context, "wujay.db", null, 2);
}
/*
* 初始化
*/
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("create table person(personId integer primary key autoincrement, name varchar(20)," +
"phone varchar(12) null,amount varchar(20) null)");
}
/*
* 更新操作
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("alter table person add amount integer null");
}
}
在这个类中实现数据库的创建以及更新操作。 PersonProvider.java代码如下：
package com.wujay.provider.db;
import com.wujay.provider.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 dbOpenHelper;
private static final UriMatcher MATCHER = new UriMatcher(UriMatcher.NO_MATCH);
private static int PERSONS = 1; //对所有数据操作
private static int PERSON = 2; //操作指定的数据
/*
* 静态代码块
*/
static{
MATCHER.addURI("com.wujay.providers.personprovider", "person", PERSONS);
MATCHER.addURI("com.wujay.providers.personprovider", "person/#", PERSON);
}
/*
* 初始化
*/
@Override
public boolean onCreate() {
dbOpenHelper = new DBOpenHelper(getContext());
return false;
}
/*
* 根据条件查询
*/
@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
int num = 0;
switch (MATCHER.match(uri)) {
case 1:
return db.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 += " and "+selection;
}
return db.query("person", projection, where, selectionArgs, null, null, sortOrder);
default:
throw new IllegalArgumentException("this is a unknown URI:"+uri);
}
}
/*
* 用于返回当前Uri所代表的数据的MIME类型
*/
@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";
default:
throw new IllegalArgumentException("this is a unknown URI:"+uri);
}
}
/*
* 插入数据
*/
@Override
public Uri insert(Uri uri, ContentValues values) {
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
switch (MATCHER.match(uri)) {
case 1:
long rowId = db.insert("person", "name", values);
Uri insertUri = ContentUris.withAppendedId(uri, rowId);
break;
default:
throw new IllegalArgumentException("this is a unknown URI:"+uri);
}
return null;
}
/*
* 删除数据
*/
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
int num = 0;
switch (MATCHER.match(uri)) {
case 1:
num = db.delete("person", selection, selectionArgs);
break;
case 2:
long rowId = ContentUris.parseId(uri);
String where = "personId=" + rowId;
if(selection!=null && "".equals(selection.trim())){
where += " and "+selection;
}
num = db.delete("person", where, selectionArgs);
break;
default:
throw new IllegalArgumentException("this is a unknown URI:"+uri);
}
return num;
}
/*
* 修改数据
*/
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
int num = 0;
switch (MATCHER.match(uri)) {
case 1:
num = db.update("person", values, selection, selectionArgs);
break;
case 2:
long rowId = ContentUris.parseId(uri);
String where = "personId=" + rowId;
if(selection!=null && "".equals(selection.trim())){
where += " and "+selection;
}
num = db.update("person", values, where, selectionArgs);
break;
default:
throw new IllegalArgumentException("this is a unknown URI:"+uri);
}
return num;
}
}
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