使用SQLiteOpenHelper管理SD卡中的数据库

本人在网上找了好多大牛的资料，研究了几天终于调试出来了。以下是笔记；

SQLiteOpenHelper是Android框架为我们提供的一个非常好的数据库打开、升级与关闭的工具类。但是这个工具类会自动把db文件创建到“ /data/data/com.*.*(package name)/” 目录下，这么做可能是与Android文件系统的设计思路有关。

但是在实战过程中，我们可能有各种原因需要自定义db文件路径（例如db文件较大放到sd卡更安全等等），相信很多人都遇到了这个需求，网上也有很多解决方法，这些方法大多是抛弃Android框架为我们提供的SQLiteOpenHelper类，自己重头写一个DbHelper类完成自定义路径的数据库打开关闭等。这么做虽然可以解决问题，但并不是一个最好的方法，因为自己写的DbHelper可靠性和功能自然难和google巨匠相提并论。

所以可以采用这样一种方法，通过继承和添加代码，并复用SQLiteOpenHelper的代码，来解决自定义db路径的问题。

首先我们来分析一下SQLiteOpenHelper的源代码。getReadableDatabase()和getWritableDatabase()在内部都是调用getDatabaseLocked()。getDatabaseLocked()的源代码很容易理解，分析得知：

• 如果以只读方式打开，是通过mContext.getDatabasePath(mName)来获取db文件的路径并使用SQLiteDatabase.openDatabase()直接打开数据库；
• 如果以读写方式打开，是通过mContext.openOrCreateDatabase(mName, mEnableWriteAheadLogging ? Context.MODE_ENABLE_WRITE_AHEAD_LOGGING : 0, mFactory, mErrorHandler)打开或创建数据库。

所以我们需要改变mContext的行为。Android框架提供了一个ContextWrapper类，是Context的一个代理，可以通过继承的方式拉改变Context的行为，所以我们继承ContextWrapper，复写它的openOrcreatDatabase()方法，然后实例化SQLiteOpenHelper时，传我们复写的Context进去就可以了。

代码如下：

package com.slc.qhfpsj.DAO;

import android.content.Context;
import android.content.ContextWrapper;
import android.database.DatabaseErrorHandler;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

import java.io.File;

/**
 * Created by Administrator on 2015/11/22.
 * Coder:Mengjinluohua
 * version:1.0
 */
public class DatabaseContext extends ContextWrapper {
    public DatabaseContext(Context base) {
        super(base);
    }

    /**
     * 获得数据库路径，如果不存在，则创建对象对象
     *
     * @param    name
     *
     */
    @Override
    public File getDatabasePath(String name) {
//        return super.getDatabasePath(name);
        //判断是否存在sd卡
        boolean sdExist = android.os.Environment.MEDIA_MOUNTED.equals(android.os.Environment.getExternalStorageState());
        if (!sdExist) {//如果不存在,
            Log.e("SD卡管理：", "SD卡不存在，请加载SD卡");
            return null;
        } else {//如果存在
            //获取sd卡路径
//            String dbDir= FileUtils.getFlashBPath();
            String dbDir = android.os.Environment.getExternalStorageDirectory().getAbsolutePath();//sd卡路径
            dbDir += "/DB";//数据库所在目录  在这里修改SD卡下文件的保存路径
//            String dbPath = dbDir + "/" + name;//数据库路径
            File dbfile = getFilePath(dbDir, name);
            return dbfile;

        }
    }


    private File getFilePath(String dbDir, String name) {
        File file = null;
        makeRootDirectory(dbDir);
        try {
            file = new File(dbDir+ "/" + name);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return file;


    }

    private void makeRootDirectory(String dbPath) {
        File file = null;
        try {
            file = new File(dbPath);
            if (!file.exists()) {
                file.mkdir();
            }
        } catch (Exception e) {

        }
    }



    @Override
    public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory) {
        SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), null);
        return result;
    }
    @Override
    public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory,
                                               DatabaseErrorHandler errorHandler) {
        SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), null);
        return result;
    }

}

然后我们在继承SQLiteOpenHelper时这么写就可以了：

package com.slc.qhfpsj.DAO;

import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

/**
 * Created by Administrator on 2015/11/23.
 * Coder:Mengjinluohua
 * version:1.0
 */
public class SdCardDBHelper extends SQLiteOpenHelper {

    public static final String TAG = "SdCardDBHelper";
    /**
     * 数据库名称
     **/
    public static String DATABASE_NAME = "sddb.db";

    /**
     * 数据库版本
     **/
    public static int DATABASE_VERSION = 2;

    /**
     * 构造函数
     *
     * @param    context 上下文环境
     **/
    public SdCardDBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        Log.e(TAG, "开始创建数据库表");
        try{
            //创建用户表(user)
            db.execSQL("create table PovertyFamilyMumberListInfoTab (_id integer primary key autoincrement,name varchar(20)," +
                    "ID varchar(30),sex varchar（10）,relationship varchar(20),people varchar(10),educationDegree varchar(30),studentCondition varchar(30)," +
                    "healthCondition varchar(30),workAbility varchar(30),workCondition varchar(30),workTime varchar(30),isJoinVillageMedical integer(10)," +
                    "isJoinCityOrTownMedical integer(10))");
            Log.e(TAG, "创建离线所需数据库表成功");

        }
        catch(SQLException se){
            se.printStackTrace();
            Log.e(TAG, "创建离线所需数据库表失败");


        }

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

这样使用：建立一个 DAO类 操作数据库

public class Jbqk_listinfoDAO {

    private final SdCardDBHelper sdCardDBHelper;

    public Jbqk_listinfoDAO(Context context) {
        DatabaseContext databaseContext = new DatabaseContext(context);
        sdCardDBHelper = new SdCardDBHelper(databaseContext);
    }
 
    public boolean add(String name, String sex, String ID, String relationship, String people, String educationDegree, String studentCondition,
                       String healthCondition,
                       String workAbility, String workCondition, String workTime, String isJoinVillageMedical, String isJoinCityOrTownMedical) {

        SQLiteDatabase db = sdCardDBHelper.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put("ID", ID);
        contentValues.put("name", name);
        contentValues.put("sex", sex);
        contentValues.put("relationship", relationship);
        contentValues.put("people", people);
        contentValues.put("educationDegree", educationDegree);
        contentValues.put("studentCondition", studentCondition);
        contentValues.put("healthCondition", healthCondition);
        contentValues.put("workAbility", workAbility);
        contentValues.put("workCondition", workCondition);
        contentValues.put("workTime", workTime);
        contentValues.put("isJoinVillageMedical", isJoinVillageMedical);
        contentValues.put("isJoinCityOrTownMedical", isJoinCityOrTownMedical);

        long rowid = db.insert("PovertyFamilyMumberListInfoTab", null, contentValues);

        if (rowid == -1) {
            return false;
        } else {
            return true;
        }


    }
}

 测试代码：

 public void testAdd() {
        DatabaseContext databaseContext = new DatabaseContext(mcontext);
        Jbqk_listinfoDAO Dao = new Jbqk_listinfoDAO(databaseContext);


        for (int i = 0; i < Cheeses.name.length; i++) {
            String name = Cheeses.name[i];
            String ID = Cheeses.ID[i];
            String sex = Cheeses.sex[i];
            String relationship = Cheeses.relationship[i];
            String people = Cheeses.people[i];
            String educationDegree = Cheeses.educationDegree[i];
            String studentCondition = Cheeses.studentCondition[i];
            String healthCondition = Cheeses.healthCondition[i];
            String workAbility = Cheeses.workAbility[i];
            String workCondition = Cheeses.workCondition[i];
            String workTime = Cheeses.workTime[i];
            String isJoinVillageMedical = Cheeses.isJoinVillageMedical[i];
            String isJoinCityOrTownMedical = Cheeses.isJoinCityOrTownMedical[i];

            boolean add = Dao.add(name, sex, ID, relationship, people, educationDegree, studentCondition, healthCondition,
                    workAbility, workCondition, workTime, isJoinVillageMedical, isJoinCityOrTownMedical);
        }
    }