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我正在研究使用SQLite上的数据库的应用程序。我有一个自定义DatabaseHelper类，它创建两个不同的sqlite数据库并从资产文件夹中复制它们。我有的问题是我可以“T集不同situations.Here要使用哪个数据库是我DatabaseHelper类看起来像：Android更改数据库
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DataBaseHelper extends SQLiteOpenHelper{
private static SQLiteDatabase sqliteDb;
private static DataBaseHelper instance;
private static final int DATABASE_VERSION = 1;
// the default database path is :
// /data/data/pkgNameOfYourApplication/databases/
private static String DB_PATH_PREFIX = "/data/data/";
private static String DB_PATH_SUFFIX = "/databases/";
private static final String TAG = "DataBaseHelper";
private Context context;
/***
* Contructor
*
* @param context
* : app context
* @param name
* : database name
* @param factory
* : cursor Factory
* @param version
* : DB version
*/
public DataBaseHelper(Context context, String name,
CursorFactory factory, int version) {
super(context, name, factory, version);
this.context = context;
Log.i(TAG, "Create or Open database : " + name);
}
/***
* Initialize method
*
* @param context
* : application context
* @param databaseName
* : database name
*/
public static void initialize(Context context, String databaseName) {
if (instance == null) {
/**
* Try to check if there is an Original copy of DB in asset
* Directory
*/
if (!checkDatabase(context, databaseName)) {
// if not exists, I try to copy from asset dir
try {
copyDataBase(context, databaseName);
} catch (IOException e) {
Log.e(TAG,"Database "+ databaseName+" does not exists and there is no Original Version in Asset dir");
}
}
Log.i(TAG, "Try to create instance of database (" + databaseName
+ ")");
instance = new DataBaseHelper(context, databaseName,
null, DATABASE_VERSION);
sqliteDb = instance.getWritableDatabase();
Log.i(TAG, "instance of database (" + databaseName + ") created !");
}
}
/***
* Static method for getting singleton instance
*
* @param context
* : application context
* @param databaseName
* : database name
* @return : singleton instance
*/
public static final DataBaseHelper getInstance(
Context context, String databaseName) {
initialize(context, databaseName);
return instance;
}
/***
* Method to get database instance
*
* @return database instance
*/
public SQLiteDatabase getDatabase() {
return sqliteDb;
}
@Override
public void onCreate(SQLiteDatabase db) {
Log.d(TAG, "onCreate : nothing to do");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.d(TAG, "onUpgrade : nothing to do");
}
/***
* Method for Copy the database from asset directory to application's data
* directory
*
* @param databaseName
* : database name
* @throws IOException
* : exception if file does not exists
*/
public void copyDataBase(String databaseName) throws IOException {
copyDataBase(context, databaseName);
}
/***
* Static method for copy the database from asset directory to application's
* data directory
*
* @param aContext
* : application context
* @param databaseName
* : database name
* @throws IOException
* : exception if file does not exists
*/
private static void copyDataBase(Context aContext, String databaseName)
throws IOException {
// Open your local db as the input stream
InputStream myInput = aContext.getAssets().open(databaseName);
// Path to the just created empty db
String outFileName = getDatabasePath(aContext, databaseName);
Log.i(TAG, "Check if create dir : " + DB_PATH_PREFIX
+ aContext.getPackageName() + DB_PATH_SUFFIX);
// if the path doesn't exist first, create it
File f = new File(DB_PATH_PREFIX + aContext.getPackageName()
+ DB_PATH_SUFFIX);
if (!f.exists())
f.mkdir();
Log.i(TAG, "Trying to copy local DB to : " + outFileName);
// 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();
Log.i(TAG, "DB (" + databaseName + ") copied!");
}
/***
* Method to check if database exists in application's data directory
*
* @param databaseName
* : database name
* @return : boolean (true if exists)
*/
public boolean checkDatabase(String databaseName) {
return checkDatabase(context, databaseName);
}
/***
* Static Method to check if database exists in application's data directory
*
* @param aContext
* : application context
* @param databaseName
* : database name
* @return : boolean (true if exists)
*/
private static boolean checkDatabase(Context aContext, String databaseName) {
SQLiteDatabase checkDB = null;
try {
String myPath = getDatabasePath(aContext, databaseName);
Log.i(TAG, "Trying to conntect to : " + myPath);
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READONLY);
Log.i(TAG, "Database " + databaseName + " found!");
checkDB.close();
} catch (SQLiteException e) {
Log.i(TAG, "Database " + databaseName + " does not exists!");
}
return checkDB != null ? true : false;
}
/***
* Method that returns database path in the application's data directory
*
* @param databaseName
* : database name
* @return : complete path
*/
@SuppressWarnings("unused")
private String getDatabasePath(final String databaseName) {
return getDatabasePath(context, databaseName);
}
/***
* Static Method that returns database path in the application's data
* directory
*
* @param aContext
* : application context
* @param databaseName
* : database name
* @return : complete path
*/
private static String getDatabasePath(Context aContext, String databaseName) {
return DB_PATH_PREFIX + aContext.getPackageName() + DB_PATH_SUFFIX
+ databaseName;
}
public boolean executeQuery(String tableName,ContentValues values){
return execQuery(tableName,values);
}
private static boolean execQuery(String tableName,ContentValues values){
sqliteDb = instance.getWritableDatabase();
sqliteDb.insert(tableName, null, values);
return true;
}
public boolean updateSQL(String tableName,String key,String value){
return updateData(tableName,key,value);
}
private static boolean updateData(String tableName,String key,String value){
sqliteDb = instance.getWritableDatabase();
String where = "";
ContentValues values = new ContentValues();
values.put(key, value);
values.put(key, value);
sqliteDb.update(tableName, values, where, new String[] {"3"});
return true;
}
public boolean deleteSQL(String tableName){
return deleteData(tableName);
}
private static boolean deleteData(String tableName){
sqliteDb = instance.getWritableDatabase();
String where = "";
sqliteDb.delete(tableName, where, new String[] {"5"});
return true;
}
public Cursor executeSQLQuery(String query){
return sqliteDb.rawQuery(query,null);
}
/**
* Make queries
*
*/
}
我有两个数据库：第一个是system.sqlite，第二个user.sqlite。 我初始化的第一个我的应用程序启动时：
dbHelper = new DataBaseHelper(this, "system.sqlite", null, 1);
DataBaseHelper.initialize(this, "system.sqlite");
dbHelper.checkDatabase("system.sqlite");
我初始化用户的数据库以同样的方式，在我的应用程序，当用户第一次登录。 登录后，我有几个非活动课，我需要在这两个分贝的的插入一些数据：
ContentValues values = new ContentValues();
values.put("objectId", 75);
values.put("objectOid", "boom");
values.put("serverName", "shit");
values.put("locale", "en_US");
values.put("deviceId", 45);
dbHelper.executeQuery("users",values);
但问题是，即使开放时，我比接近一流system.sqlite它..并尝试打开从另一个类仍然试图写入系统数据库的user.sqlite。例如：
dbHelper = new DataBaseHelper(context, "system.sqlite", null, 1);
dbHelper.initialize(context, "system.sqlite");
dbHelper.getWritableDatabase();
//do some work
dbHelper.close();
它实际上并不工作。 任何建议如何让这些东西起作用？
如果我删除所有静态字段，它会在此行引发异常：return sqliteDb.rawQuery（query，null）; –
您还需要修复引用静态字段的代码。 –
现在我卡在这一行：return DB_PATH_PREFIX + aContext.getPackageName（）+ DB_PATH_SUFFIX + databaseName; ---这是throwin'NullPointerException。 –