Android程序中读取使用已有的SQLite数据库

方法一:

先在 Manifest 里添加权限：

<span style="font-size:12px;"><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /><uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /></span>

第一步先判断在指定的路劲是否存在，不存在就创建。第二步将android的资源下的数据库复制到指定路径下面。第三步就是根据指定路径打开或者创建数据库，然后得到操作数据库的对象，得到操作数据库的对象了，自然就可以对数据库中的表进行增删改查等操作了。

<span style="font-size:12px;">SQLiteDatabase db;    private final String DATABASE_PATH = android.os.Environment            .getExternalStorageDirectory().getAbsolutePath() + "/vote";    private String DATABASE_FILENAME = "db_vote.db";// 初始化数据库    private SQLiteDatabase openDatabase() {        try {            String databaseFilename = DATABASE_PATH + "/" + DATABASE_FILENAME;            File dir = new File(DATABASE_PATH);            if (!dir.exists())                dir.mkdir();            if (!(new File(databaseFilename)).exists()) {                InputStream is = getResources().openRawResource(R.raw.db_vote);                FileOutputStream fos = new FileOutputStream(databaseFilename);                byte[] buffer = new byte[8192];                int count = 0;                while ((count = is.read(buffer)) > 0) {                    fos.write(buffer, 0, count);                }                fos.close();                is.close();            }            db = SQLiteDatabase.openOrCreateDatabase(databaseFilename, null);            return db;        } catch (Exception e) {            e.printStackTrace();        }        return null;    }</span>

方法二：
1. 准备SQLite database文件

    假设你已经创建了一个sqlite数据库，我们需要对其进行一些修改。

   （译者注：这里原文是推荐了一个SQLite数据库管理软件，这个我觉得可以随自己的喜好，最Windows下面有多款可视化的SQlite数据库管理软件，可以方便的读取，编辑数据库，例如我用的是sqlitestudio

打开数据库，添加一个新的table “android_metadata"，插入一行数据，具体的SQL如下：

<span style="font-size:12px;">    CREATE TABLE "android_metadata" ("locale" TEXT DEFAULT 'en_US')            INSERT INTO "android_metadata" VALUES ('en_US')  </span>

（译者注：上面两行是表明需要进行的操作，具体可以直接在sqlitesstudio中完成）

    然后你需要对你数据表格的primary id 列重命名为 “_id”，这样Adroid会知道怎么对id列进行绑定，你可以很容易的在SQlite数据库管理软件中进行列编辑。

    这两步之后，你的sqlite数据库文件就准备好了。

  （这里我保留了id列，即没有对其进行重命名，测试证明也是没有问题的）

2. 在你的Android程序中复制，打开以及访问数据库

    现在把你上一步准备好的数据库文件放在“assets”文件夹下面，然后通过继承 SQLiteOpenHelper类来创建一个Database Helper类，

你的DataBaseHelper类大致可以如下：

    <span style="font-size:12px;">public class DataBaseHelper extends SQLiteOpenHelper{                 //The Android's default system path of your application database.          private static String DB_PATH = "/data/data/YOUR_PACKAGE/databases/";                 private static String DB_NAME = "myDBName";                 private SQLiteDatabase myDataBase;                  private final Context myContext;                 /**          * Constructor          * Takes and keeps a reference of the passed context in order to access to the application assets and resources.          * @param context          */          public DataBaseHelper(Context context) {                     super(context, DB_NAME, null, 1);              this.myContext = context;          }                  /**          * Creates a empty database on the system and rewrites it with your own database.          * */          public void createDataBase() throws IOException{                     boolean dbExist = checkDataBase();                     if(dbExist){                  //do nothing - database already exist              }else{                         //By calling this method and empty database will be created into the default system path                     //of your application so we are gonna be able to overwrite that database with our database.                  this.getReadableDatabase();                         try {                             copyDataBase();                         } catch (IOException e) {                             throw new Error("Error copying database");                         }              }                 }                 /**          * Check if the database already exist to avoid re-copying the file each time you open the application.          * @return true if it exists, false if it doesn't          */          private boolean checkDataBase(){                     SQLiteDatabase checkDB = null;                     try{                  String myPath = DB_PATH + DB_NAME;                  checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);                     }catch(SQLiteException e){                         //database does't exist yet.                     }                     if(checkDB != null){                         checkDB.close();                     }                     return checkDB != null ? true : false;          }                 /**          * Copies your database from your local assets-folder to the just created empty database in the          * system folder, from where it can be accessed and handled.          * This is done by transfering bytestream.          * */          private void copyDataBase() throws IOException{                     //Open your local db as the input stream              InputStream myInput = myContext.getAssets().open(DB_NAME);                     // Path to the just created empty db              String outFileName = DB_PATH + DB_NAME;                     //Open the empty db as the output stream              OutputStream myOutput = new FileOutputStream(outFileName);                     //transfer bytes from the inputfile to the outputfile              byte[] buffer = new byte[1024];              int length;              while ((length = myInput.read(buffer))>0){                  myOutput.write(buffer, 0, length);              }                     //Close the streams              myOutput.flush();              myOutput.close();              myInput.close();                 }                 public void openDataBase() throws SQLException{                     //Open the database              String myPath = DB_PATH + DB_NAME;              myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);                 }                 @Override          public synchronized void close() {                         if(myDataBase != null)                      myDataBase.close();                         super.close();                 }                 @Override          public void onCreate(SQLiteDatabase db) {                 }                 @Override          public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {                 }                     // Add your public helper methods to access and get content from the database.             // You could return cursors by doing "return myDataBase.query(....)" so it'd be easy             // to you to create adapters for your views.             }  </span>

就这样。

    现在你可以创建一个新的DataBaseHelper实例，然后调用createDataBase()，然后再调用openDataBase()方法，记住修改DB_PATH字符串中“YOUR_PACKAGE”为你真正的package名称（也就是说com.examplename.myapp）

以下是示范代码：

   <span style="font-size:12px;"> ...                   DataBaseHelper myDbHelper = new DataBaseHelper();             myDbHelper = new DataBaseHelper(this);                   try {                    myDbHelper.createDataBase();                } catch (IOException ioe) {                    throw new Error("Unable to create database");                }                try {                    myDbHelper.openDataBase();                }catch(SQLException sqle){                    throw sqle;                }                   ...  </span>