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>