我正在创建一个使用现有sqlite数据库的Dictionary应用程序。我已将数据库放在assets文件夹中，并且我在第一次启动应用程序时使用以下代码复制数据库。 （我从this帖子中借用了这个想法）
DatabaseHelper.java
public class DatabaseHelper {
private static String DB_PATH = "";
private static String DB_NAME = "abc.sqlite";
private SQLiteDatabase myDatabase;
private Context myContext;
public DatabaseHelper(Context context) {
myContext = context;
if (android.os.Build.VERSION.SDK_INT >= 17)
DB_PATH = context.getApplicationInfo().dataDir + "/databases/";
else
DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
Log.d("path", DB_PATH);
}
public void copyDatabase() {
InputStream myInput;
OutputStream outStream;
try {
myInput = myContext.getAssets().open(DB_NAME);
String file = DB_PATH + DB_NAME;
outStream = new FileOutputStream(file);
byte[] buffer = new byte[1024];
int length = 0;
while ((length = myInput.read(buffer)) >= 0) {
outStream.write(buffer, 0, length);
}
outStream.flush();
myInput.close();
outStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
然后我将上述copyDatabase()方法称为MainActivity。这是代码。
public class MainActivity extends Activity {
DatabaseHelper myDbHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layout);
myDbHelper = new DatabaseHelper(getApplicationContext());
myDbHelper.copyDatabase();
}
}
但问题是Android不会复制数据库。我使用了Log工具，我发现while循环永远不会运行。 这段代码有什么问题。 感谢。
答案 0 :(得分：2)
更改你的while循环如下：
除了您的条件>=大于或等于将其更改为仅>大于
while ((length = myInput.read(buffer)) > 0) {
outStream.write(buffer, 0, length);
}
尝试下面的代码，这对你来说就像魅力一样。
public class DataBaseHelper extends SQLiteOpenHelper {
private Context mycontext;
private String DB_PATH;
private static String DB_NAME = "abc.sqlite";
public SQLiteDatabase myDataBase;
public DataBaseHelper(Context context) throws IOException {
super(context,DB_NAME,null,1);
this.mycontext=context;
boolean dbexist = checkdatabase();
if (dbexist) {
opendatabase();
} else {
System.out.println("Database doesn't exist");
createdatabase();
}
}
public void createdatabase() throws IOException {
boolean dbexist = checkdatabase();
if(!dbexist) {
this.getReadableDatabase();
try {
copydatabase();
} catch(IOException e) {
throw new Error("Error copying database");
}
}
}
private boolean checkdatabase() {
boolean checkdb = false;
try {
String myPath = DB_PATH + DB_NAME;
File dbfile = new File(myPath);
checkdb = dbfile.exists();
} catch(SQLiteException e) {
System.out.println("Database doesn't exist");
}
return checkdb;
}
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 byte to inputfile to 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_READWRITE);
}
public synchronized void close() {
if(myDataBase != null) {
myDataBase.close();
}
super.close();
}
}
在您的MainActivity中，您现在需要创建其他人将自行管理的DatabaseHelper课程的实例。
public class MainActivity extends Activity {
DatabaseHelper myDbHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layout);
myDbHelper = new DatabaseHelper(MainActivity.this);
}
}
答案 1 :(得分：1)
从
更改此内容while ((length = myInput.read(buffer)) >= 0) {
outStream.write(buffer, 0, length);
}
到
while ((length = myInput.read(buffer)) >0) {
outStream.write(buffer, 0, length);
}
最好在oncreate（）方法上复制数据库，因为在你的课程中你做到了。您必须在活动中调用数据库类对象并从中获取数据。首先要创建名为 DBConnect
的类public class DBConnect extends SQLiteOpenHelper {
public int GetCursor;
// ****************** Declare all the global variable
// ****************************//
private Context myContext;
public String DB_PATH = "data/data/com.xyz/databases/"; // path
// of
// your
// datbase
public static String DB_NAME = "xyz.sqlite";// your database name
static String ASSETS_DB_FOLDER = "db";
private SQLiteDatabase db;
public DBConnect(Context context, String db_name) {
super(context, db_name, null, 2);
if (db != null && db.isOpen())
close();
this.myContext = context;
DB_NAME = db_name;
try {
createDataBase();
openDataBase();
} catch (IOException e) {
// System.out.println("Exception in creation of database : "+
// e.getMessage());
e.printStackTrace();
}
}
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
// System.out.println("Database Exist");
} else {
this.getReadableDatabase();
try {
copyDatabase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
private void copyDatabase() throws IOException {
InputStream input = myContext.getAssets().open(DB_NAME);
String outputFileName = DB_PATH + DB_NAME;
OutputStream output = new FileOutputStream(outputFileName);
byte[] buffer = new byte[1024];
int length;
while ((length = input.read(buffer)) > 0) {
output.write(buffer, 0, length);
}
// Close the streams
output.flush();
output.close();
input.close();
// System.out.println(DB_NAME + "Database Copied !");
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
public void openDataBase() throws SQLException {
// Open the database
String myPath = DB_PATH + DB_NAME;
db = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
}
public boolean isOpen() {
if (db != null)
return db.isOpen();
return false;
}
@Override
public synchronized void close() {
if (db != null)
db.close();
super.close();
}
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
// System.out.println("My Pathe is:- " + myPath);
// System.out.println("Open");
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
// System.out.println("checkDB value:" + checkDB);
// System.out.println("My Pathe is:- " + myPath);
} catch (Exception e) {
// database does't exist yet.
}
if (checkDB != null) {
// System.out.println("Closed");
checkDB.close();
// System.out.println("My db is:- " + checkDB.isOpen());
}
return checkDB != null ? true : false;
}
public Cursor execCursorQuery(String sql) {
Cursor cursor = null;
try {
cursor = db.rawQuery(sql, null);
GetCursor = cursor.getCount();
Log.i("Inside execCursorQuery try", sql);
} catch (Exception e) {
Log.i("Inside execCursorQuery exception", e.getMessage());
}
return cursor;
}
public void execNonQuery(String sql) {
try {
db.execSQL(sql);
// Log.d("SQL", sql);
} catch (Exception e) {
// Log.e("Err", e.getMessage());
} finally {
// closeDb();
}
}
在您的活动中，您应该通过以下方式调用它：
public class MainActivity extends Activity {
DBConnect db;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.layout);
db= new DBConnect(MainActivity.this,"databasename");
}
}
答案 2 :(得分：0)
将此代码用于从资产文件夹复制数据库
public class DataBaseHelper extends SQLiteOpenHelper
{
private static String TAG = "DataBaseHelper"; // Tag just for the LogCat window
//destination path (location) of our database on device
private static String DB_PATH = "";
//private static String DB_NAME ="(students).sqlite";// Database name
private static String DB_NAME ="virtualDB";
private SQLiteDatabase mDataBase;
private final Context mContext;
public DataBaseHelper(Context context)
{
super(context, DB_NAME, null, 1);// 1? its Database Version
DB_PATH = "/data/data/" + context.getPackageName() + "/databases/";
Log.i(TAG, DB_PATH);
this.mContext = context;
}
public void createDataBase()
{
//If database not exists copy it from the assets
boolean mDataBaseExist = checkDataBase();
if(!mDataBaseExist)
{
this.getReadableDatabase();
this.close();
try
{
//Copy the database from assests
copyDataBase();
Log.e(TAG, "createDatabase database created");
}
catch (IOException mIOException)
{
Log.i(TAG, "createDataBase "+mIOException+"");
}
}
}
//Check that the database exists here: /data/data/your package/databases/Da Name
private boolean checkDataBase()
{
File dbFile = new File(DB_PATH + DB_NAME);
//Log.v("dbFile", dbFile + " "+ dbFile.exists());
return dbFile.exists();
}
//Copy the database from assets
private void copyDataBase() throws IOException
{ try
{
InputStream mInput = mContext.getAssets().open(DB_NAME);
String outFileName = DB_PATH + DB_NAME;
OutputStream mOutput = new FileOutputStream(outFileName);
byte[] mBuffer = new byte[1024];
int mLength;
while ((mLength = mInput.read(mBuffer))>0)
{
mOutput.write(mBuffer, 0, mLength);
}
mOutput.flush();
mOutput.close();
mInput.close();
}
catch (IOException mIOException)
{ Log.i(TAG,"copyDataBase "+ mIOException+"");
}
}
//Open the database, so we can query it
public boolean openDataBase() throws SQLException
{
String mPath = DB_PATH + DB_NAME;
//Log.v("mPath", mPath);
mDataBase = SQLiteDatabase.openDatabase(mPath, null, SQLiteDatabase.CREATE_IF_NECESSARY);
//mDataBase = SQLiteDatabase.openDatabase(mPath, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS);
return mDataBase != null;
}
@Override
public synchronized void close()
{
if(mDataBase != null)
mDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase arg0) {
// TODO Auto-generated method stub
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
}
这段代码对我来说很好，我希望它可以帮到你
答案 3 :(得分：0)
请检查此支持项目以从资产 https://github.com/jgilfelt/android-sqlite-asset-helper处理sqlite数据库希望这对您有所帮助。