我是Android开发的新手。这里我将我的数据库从SQLite数据库浏览器复制到我的系统数据库。但是，当我尝试打开新创建的数据库时...我收到错误.. 这是我的代码
DBAdapter.java
public class DBAdapter extends SQLiteOpenHelper
{
private static String DB_PATH = "/data/data/com.xyz.app.demo/databases/";
private static String DB_NAME = "QuestionsDB";
private static final int DATABASE_VERSION = 1;
private SQLiteDatabase myDataBase;
private final Context myContext;
public DBAdapter(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
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;
}
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) {
}
public Cursor getAllTitles()
{
return myDataBase.query("Qus", new String[] {
"_id",
"quesion",
"XCol",
"Ycol",
"option",
"intern",
"answer",
"weight"},
null,
null,
null,
null,
null);
}
还有 questionform.java
public class questionform extends Activity{
public void onCreate(Bundle icicle)
{
super.onCreate(icicle);
setContentView(R.layout.qus_screen);
final DBAdapter db = new DBAdapter(this);
db.openDataBase();
Cursor c = db.getAllTitles();
if (c.moveToFirst())
{
do
{
DisplayTitle(c);
} while (c.moveToNext());
}
db.close();
}
private void DisplayTitle(Cursor c)
{
Toast.makeText(questionform.this,c.getString(1),Toast.LENGTH_LONG).show();
}
}
更新
questionform.java的新代码：
public void onCreate(Bundle icicle)
{
super.onCreate(icicle);
setContentView(R.layout.qus_screen);
final DBAdapter db = new DBAdapter(this);
try {
db.createDataBase();
} catch (IOException e) {
// TODO Auto-generated catch block
}
db.openDataBase();
Cursor c = db.getAllTitles();
if (c.moveToFirst())
{
do
{
DisplayTitle(c);
} while (c.moveToNext());
}
db.close();
}
答案 0 :(得分：0)
按如下方式拨打两次
final DBAdapter db ;
try{
db = new DBAdapter(this);
db.openDataBase();
}catch(Exception e)
{ db = new DBAdapter(this);
db.openDataBase();
}
答案 1 :(得分：0)
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.annotation.SuppressLint;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseAssets extends SQLiteOpenHelper {
String DB_PATH = null;
private static String DB_NAME = "androidDb.db";
public static final String TABLE_USERS = "Tbl_Users";
public static final String TABLE_Product = "Tbl_Product";
// TABLE_CONTENT
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
*/
@SuppressLint("SdCardPath")
public DatabaseAssets(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
// DB_PATH = "/data/data/" + context.getPackageName() + "/" +
// "databases/";
DB_PATH = "/data/data/" + context.getPackageName() + "/" + "databases/";
}
/**
* 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");
}
}
}
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
| SQLiteDatabase.CREATE_IF_NECESSARY);
} 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.
* */
public 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;
// SQLiteDatabase.NO_LOCALIZED_COLLATORS
myDataBase = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY
| SQLiteDatabase.NO_LOCALIZED_COLLATORS
| SQLiteDatabase.CREATE_IF_NECESSARY);
}
@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) {
}
// return cursor
public Cursor query(String table, String[] columns, String selection,
String[] selectionArgs, String groupBy, String having,
String orderBy) {
return myDataBase.query(TABLE_Product, null, null, null, null, null,
null);
}
}