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>