public class DatabaseHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "test.db";
private static final int DB_VERSION = 1;
private boolean DB_JUST_CREATED = false;
private Context _context;
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
_context = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
Log.d("WOD", "onCreate firing");
DB_JUST_CREATED = true;
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
@Override
public synchronized SQLiteDatabase getWritableDatabase() {
SQLiteDatabase db = super.getWritableDatabase();
// Copy db from assets folder if db was just created.
if(DB_JUST_CREATED == true) {
Log.d("WOD", "Creating db");
try {
// Open InputStream to assets db.
InputStream inStream = _context.getAssets().open(DB_NAME);
// Open OutputStream to new db.
OutputStream outStream = new FileOutputStream(db.getPath());
//transfer bytes from the input-file to the output-file
byte[] buffer = new byte[1024];
int length;
while ((length = inStream.read(buffer)) > 0)
{
outStream.write(buffer, 0, length);
}
//Close the streams
outStream.flush();
outStream.close();
inStream.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
return db;
}
}
我尝试在几个不同的活动中创建DatabaseHelper对象,每次都是同样的事情, onCreate()被触发,然后它创建一个新的数据库。我检查了DDMS文件资源管理器,果然,数据库在创建后仍保留在那里,即使我强制停止应用程序,因此甚至不应该调用onCreate。这是怎么回事?
答案 0 :(得分:3)
尝试这些对我有用
/**
* 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) {
Log.v("DB", "No DB");
// 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.getResources().openRawResource(
R.raw.diary_database);
// 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();
}
答案 1 :(得分:2)
你不应该真的重写getWritableDatabase
并以这种方式调用超类方法。
在从资产中复制文件后,您需要确保将SQLite数据库用户版本设置为当前版本,以确保在后续调用onCreate
实现时不会调用getWritableDatabase
:
db = _context.openOrCreateDatabase(DB_NAME, 0, null);
db.setVersion(DB_VERSION);