ContentProvider 的使用（1）

                                             ContentProvider 的使用（1）
1）新建Android 项目，成功后，先编写我自己的Employee 类：
/*
* Copyright (C) Mesada Technologies Co., Ltd. 2005-2011.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Mesada Technologies Co., Ltd. ("Confidential Information").
* You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license agreement
* you entered into with Mesada.
*/
package com.mesada.demo;

import android.net.Uri;

/**
* 实体类，封装了相关的一些常量信息.
*
* @author Xiaolong Long
* @date 2011-3-10
* @version 1.0
*/
public class Employee {

public static final String MIME_DIR_PREFIX = "vnd.android.cursor.dir";
public static final String MIME_ITEM_PREFIX = "vnd.android.cursor.item";
public static final String MIME_ITEM = "vnd.mesada.employee";

//MIME:表示单一数据
public static final String MIME_TYPE_SINGLE = MIME_ITEM_PREFIX + "/"
+ MIME_ITEM;
        //MIME:表示多条数据
public static final String MIME_TYPE_MULTIPLE = MIME_DIR_PREFIX + "/"
+ MIME_ITEM;

public static final String AUTHORITY = "com.mesada.demo.provider.employeeprovider";
public static final String PATH_SINGLE = "employee/#";
public static final String PATH_MULTIPLE = "employee";
public static final String STR = "content://" + AUTHORITY + "/"
+ PATH_MULTIPLE;
public static final Uri CONTENT_URI = Uri.parse(STR);

public static final String ID = "_id";
public static final String NAME = "name";
public static final String AGE = "age";
}

2）新建类，继承自ContentProvider,并重写其接口函数，代码如下：
/*
* Copyright (C) Mesada Technologies Co., Ltd. 2005-2011.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Mesada Technologies Co., Ltd. ("Confidential Information").
* You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license agreement
* you entered into with Mesada.
*/
package com.mesada.demo.provider;

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.Context;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteQueryBuilder;
import android.net.Uri;

import com.mesada.demo.Employee;

/**
* A Content Provider about Employee,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
* ContentResolver interface. A content provider is only required if you need to
* share data between multiple applications. For example, the contacts data is
* used by multiple applications and must be stored in a content provider. If
* you don't need to share data amongst multiple applications you can use a
* database directly via SQLiteDatabase.
*
*
* When a request is made via a ContentResolver the system inspects the
* authority of the given URI and passes the request to the content provider
* registered with the authority. The content provider can interpret the rest of
* the URI however it wants. The UriMatcher class is helpful for parsing URIs.
*
*
* @author Xiaolong Long
* @date 2011-3-14
* @version 1.0
*/
public class EmployeeProvider extends ContentProvider {
private static final String DB_NAME = "mesada.db";
private static final String DB_TABLE = "employee";
private static final int DB_VERSION = 1;

private Context mContext;
private SQLiteDatabase mDb;
private DBOpenHelper mDBOpenHelper;
private static final int MULTIPLE_EMPLOYEE = 1;
private static final int SINGLE_EMPLOYEE = 2;
private static final UriMatcher mUriMatcher;

static {
mUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
mUriMatcher.addURI(Employee.AUTHORITY, Employee.PATH_MULTIPLE,
MULTIPLE_EMPLOYEE);
mUriMatcher.addURI(Employee.AUTHORITY, Employee.PATH_SINGLE,
SINGLE_EMPLOYEE);
}

@Override
public String getType(Uri uri) {
// 根据给定的URI，返回相应的 MIME 类型
int code = mUriMatcher.match(uri);
switch (code) {
// 返回表示多个选项的MIME类型
case MULTIPLE_EMPLOYEE:
return Employee.MIME_TYPE_MULTIPLE;
// 返回表示单条记录的MIME类型
case SINGLE_EMPLOYEE:
return Employee.MIME_TYPE_SINGLE;
default:
throw new IllegalArgumentException("Unknown Uri:" + uri);
}
}

@Override
public boolean onCreate() {
mContext = getContext();
mDBOpenHelper = new DBOpenHelper(mContext, DB_NAME, null, DB_VERSION);
try {
mDb = mDBOpenHelper.getWritableDatabase();
} catch (Exception e) {
mDb = mDBOpenHelper.getReadableDatabase();
}
if (mDb != null) {
return true; // 数据提供者被成功载入
} else {
return false; // 数据提供者载入失败
}
}

@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
int count = 0;
int code = mUriMatcher.match(uri);
switch (code) {
case MULTIPLE_EMPLOYEE:
count = mDb.delete(DB_TABLE, selection, selectionArgs);
break;
case SINGLE_EMPLOYEE:
String str = uri.getPathSegments().get(1);
count = mDb
.delete(DB_TABLE, Employee.ID + "=" + str, selectionArgs);
break;
default:
throw new IllegalArgumentException("Unknown Uri:" + uri);
}

// 执行相应操作后，需要通知observer(观察者)，databases产生变化
getContext().getContentResolver().notifyChange(uri, null);
return count;
}

@Override
public Uri insert(Uri uri, ContentValues values) {
long id = mDb.insert(DB_TABLE, null, values);
if (id > 0) {
Uri newUri = ContentUris.withAppendedId(Employee.CONTENT_URI, id);

// 执行相应操作后，需要通知observer(观察者)，databases产生变化
getContext().getContentResolver().notifyChange(newUri, null);
return newUri;
}
throw new SQLException("Failed to insert row into " + uri);
}

@Override
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {

SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
qb.setTables(DB_TABLE);
int code = mUriMatcher.match(uri);
switch (code) {
case SINGLE_EMPLOYEE:
qb.appendWhere(Employee.ID + "=" + uri.getPathSegments().get(1));
break;
default:
break;
}
Cursor cursor = qb.query(mDb, projection, selection, selectionArgs,
null, null, sortOrder);

cursor.setNotificationUri(getContext().getContentResolver(), uri);
return cursor;
}

@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
int count;
int code = mUriMatcher.match(uri);
switch (code) {
case MULTIPLE_EMPLOYEE:
count = mDb.update(DB_TABLE, values, selection, selectionArgs);
break;
case SINGLE_EMPLOYEE:
String segment = uri.getPathSegments().get(1);
count = mDb.update(DB_TABLE, values, Employee.ID + "=" + segment,
selectionArgs);
break;
default:
throw new IllegalArgumentException("Unknow URI:" + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;

}
public class DBOpenHelper extends SQLiteOpenHelper {

private static final String DB_CREATE = "CREATE TABLE " + DB_TABLE
+ " (" + Employee.ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ Employee.NAME + " TEXT NOT NULL, " + Employee.AGE
+ " INTEGER);";

public DBOpenHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
}

@Override
public void onCreate(SQLiteDatabase db) {
try {
db.execSQL(DB_CREATE);
System.err
.println("Verify that the table was created successfully.");
} catch (SQLiteException e) {
e.printStackTrace();
System.err.println("Failed to create table.");
}

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
/*
* 当你的应用要更新升级的时候，同时新版本中数据库表结构或内容有变化，这时upgrade方法会根据你的数据库版本号来判断数据库是否升级，
* 你可以在upgrade方法中执行数据库的变化。
*/
db.execSQL("DROP TABLE IF EXISTS " + DB_TABLE);
onCreate(db);
}
}
}
注：有人问onUpgrade（，，）函数会在什么时候调用，这取决于你的版本号是否已经改变，如 public DBOpenHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
}中，如果version 改变了，就会执行该函数。

3） AndroidMainfest.xml 文件中加上provider 标签：
<?xml version="1.0" encoding="utf-8"?>
<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
package="com.mesada.demo.provider"
android:versionCode="1"
android:versionName="1.0">
<application
android:icon="@drawable/icon"
android:label="@string/app_name">
<provider
android:name=".EmployeeProvider"
android:authorities="com.mesada.demo.provider.employeeprovider" />
</application>
<uses-sdk
android:minSdkVersion="8" />
</manifest>
4）运行该项目后，即可。这样，ContentProvider 的开发工作已经完成，但它只是封闭了对数据操作的功能，如增删改查等。该项目没有相应的界面显示数据，在下一篇文章《ContentProvider 的使用（2）》说明如何调用ContentProvider，并对其进行增删改查的操作。