android：Android中用文件初始化sqlite數據庫（zz）

     不少時候在應用安裝初始化時，須要建立本地數據庫，同時爲數據庫添加數據，以後再從數據庫中讀取數據。

這裏有2個思路

    1.先在本地建立一個能支持android使用的sqlite數據庫文件,啓動時,用現成的sqlite的二進制文件進行直接copy到Android系統的數據庫路徑

    2.能夠考慮在第一次啓動時,執行數據庫初始化的sql文件.

 

1.在本地準備android能使用的sqlite數據庫文件

使用sqlite數據庫管理工具,看我的愛好(SQLite Database Browser ,Navicat Premium,)

打開數據庫,建立"android_metadata"數據表

CREATE TABLE "android_metadata" ("_id"  INTEGER PRIMARY KEY AUTOINCREMENT,"locale" TEXT DEFAULT 'en_US');//建立表
INSERT INTO "android_metadata" VALUES (1,'en_US');//插入值

 建立其餘應用須要的表..此處省略.

 

2.複製文件到應用中.

把第一步建立的數據庫文件複製到應用中的assets文件夾, asserts文件夾的路徑以下：

 

而後建立DateBaseHelper extends SQLiteOpenHelper的類文件.

代碼以下:

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.
}

 

3.如今咱們能夠建立DateBaseHelper的實現操做了.

createDataBase() //建立

openDataBase()//打開只讀數據庫

記得要更改"YOUR_PACKAGE"爲你的應用的包名

如:com.examplename.myapp

大概代碼以下:

...
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;
}
...   
      
      來源： http://zhangfan822.iteye.com/blog/1883829