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);
         }
     }