我想在我的安卓模拟器上安装我的数据库时升级它。 我已将继承自 SQLiteOpenHelper 的 DbHelper 中的 db 版本设置为 +1。
但是,当我的第一个 Activity 加载时,我实例化了我的 DbHelper,我希望 SQLiteOpenHelper 调用 onUpgrade,因为 db 版本现在更新了。但是它永远不会被调用。我想知道我是否缺少某些东西。 DbHelper 用于与新版本进行比较的版本存储在哪里?为什么这不起作用?
我实际上是将数据库从 Assets 文件夹复制到数据文件夹中,而不是重新创建架构。
public class DbHelper extends SQLiteOpenHelper {
private static final String TAG = "DbHelper";
static final String DB_NAME = "caddata.sqlite";
static final int DB_VERSION = 4;
private static String DB_PATH = "";
private Context myContext;
private SQLiteDatabase myDataBase;
public DbHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
this.myContext = context;
DB_PATH = "/data/data/"
+ context.getApplicationContext().getPackageName()
+ "/databases/";
}
public DbHelper open() throws SQLException {
myDataBase = getWritableDatabase();
Log.d(TAG, "DbHelper Opening Version: " + this.myDataBase.getVersion());
return this;
}
@Override
public synchronized void close() {
if (myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
Log.d(TAG, "onCreate called");
try {
createDataBase();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if ( newVersion > oldVersion)
{
Log.d(TAG, "New database version exists for upgrade.");
try {
Log.d(TAG, "Copying database...");
copyDataBase();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (!dbExist) {
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
openDataBaseForRead();
}
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY
| SQLiteDatabase.NO_LOCALIZED_COLLATORS);
Log.d(TAG, "db exists");
} catch (SQLiteException e) {
// database does't exist yet.
Log.d(TAG, "db doesn't exist");
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
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[2048];
int length;
while ((length = myInput.read(buffer)) > 0) {
myOutput.write(buffer, 0, length);
}
// Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
myDataBase.setVersion(DB_VERSION);
}
public void openDataBaseForRead() throws SQLException {
// Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
public void openDataBaseForWrite() throws SQLException {
// Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE | SQLiteDatabase.NO_LOCALIZED_COLLATORS );
}
}
最佳答案
这是来自SQLiteOpenHelper.getWritableDatabase()
的代码 fragment :
int version = db.getVersion();
if (version != mNewVersion) {
db.beginTransaction();
try {
if (version == 0) {
onCreate(db);
} else {
if (version > mNewVersion) {
onDowngrade(db, version, mNewVersion);
} else {
onUpgrade(db, version, mNewVersion);
}
}
db.setVersion(mNewVersion);
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
}
onOpen(db);
如您所见,onCreate()
或 onUpgrade()
在对 getWritableDatabase()
的调用中被调用。
当您需要 SQLiteDatabase
的实例时,您必须使用这些调用。您不应该使用自己的方法,除非它们是围绕 getWritableDatabase
或 getReadableDatabase
方法的包装器。
关于android - 为什么在 Android sqlite 数据库上没有调用 onUpgrade()?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/7647566/