我是Android的初学者，使用现有的数据库开发一个简单的应用程序。我发现我无法直接使用它，并且必须先将其复制到本地数据目录，然后再对其执行查询[/ data / data /]。我已经声明了读取和写入权限，因为有些人建议访问存储在assets文件夹中的数据库。
现在，针对问题：我无法访问存储在Assets文件夹中的数据库。我尝试过AssetDatabaseOpenHelper（）等等。所有这些都表明我复制了我无法做到的数据库。我在下面发布了我的代码：
package com.vrsit.myfriendsapp;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DBHandler extends SQLiteOpenHelper {
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.vrsit.myfriendsapp/databases/";
// Database Name
private static String DB_NAME = "vrs.db";
// Logcat tag
private static final String LOG = "database";
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "vrs.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
public static long INSERT_ERROR = -1;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
*
* @param context
*/
public DBHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
*/
public void createDataBase() throws IOException {
Log.d(LOG, "Calling checkDataBase() Method");
boolean dbExist = checkDataBase();
if (dbExist) {
//do nothing - database already exist
Log.d(LOG, "!!!Database Found!!!");
} 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.
Log.d(LOG, "!!!Creating Empy Database!!!");
this.getReadableDatabase();
this.close();
Log.d(LOG, "!!!Coping Database!!!");
copyDataBase();
}
}
/**
* 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;
Log.d(LOG, "looking database at " + myPath);
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
Log.e(LOG, "Exception: database does't exist yet");
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;*/
File dbFile = new File(DB_PATH + DB_NAME);
return dbFile.exists();
}
/**
* 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() {
Log.d("LOG", "Input Entered");
//Open your local db as the input stream
try {
Log.d("LOG", "Input Found");
InputStream myInput = myContext.getAssets().open(DB_NAME, 3);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
Log.d(LOG, "Coping database from " + myInput + ", to " + outFileName);
//Open the empty db as the output stream
File out = new File(outFileName);
out.setWritable(true);
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();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
public void openDataBase() throws SQLException {
openDataBase(true);
}
public void openDataBase(boolean readonly) throws SQLException {
//Open the database
String myPath = DB_PATH + DB_NAME;
if (readonly)
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
else
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
@Override
public synchronized void close() {
if (myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
}
答案 0 :(得分：1)
这种方式让我可以使用资产文件夹中保存的数据库。
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
DB_PATH = context.getDatabasePath(DatabaseHelper.DB_NAME).toString()
.replace(DB_NAME, "");
this.mContext = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
database = db;
String CREATE_TABLE = "CREATE TABLE QUERY";
database.execSQL(CREATE_LOCATION_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
database = db;
}
public boolean createDatabase() {
boolean isExist = checkDBExists();
if (isExist) {
System.out.println("DB Exists...");
openDatabase();
onUpgrade(database, database.getVersion(), DB_VERSION);
close();
} else {
System.out.println("Copying DB...");
this.getReadableDatabase();
copyDatabase();
}
return isExist;
}
private boolean checkDBExists() {
try {
File file = new File(DB_PATH + DB_NAME);
if (file.exists()) {
return true;
}
} catch (Exception e) {
e.printStackTrace();
return false;
}
return false;
}
private void copyDatabase() {
try {
InputStream is = mContext.getAssets().open("databases/" + DB_NAME);
OutputStream fos = new FileOutputStream(DB_PATH + DB_NAME);
int length = 0;
byte[] buffer = new byte[1024];
while ((length = is.read(buffer)) > 0) {
fos.write(buffer, 0, length);
}
fos.flush();
fos.close();
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public void openDatabase() {
database = SQLiteDatabase.openDatabase(DB_PATH + DB_NAME, null,
SQLiteDatabase.OPEN_READWRITE);
}
public synchronized void close() {
if (database != null)
database.close();
SQLiteDatabase.releaseMemory();
super.close();
}