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>
转载:http://blog.csdn.net/chaoyu168/article/details/50316885