本文介绍了如何从Android中的帮助类初始化sqlite数据库的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着跟版网的小编来一起学习吧！
问题描述
我有一个扩展 SQLiteOpenHelper 的自定义 DataBaseHelper 类，如下所示:
I have a custom DataBaseHelper class which extends SQLiteOpenHelper,which looks like this :
package com.stampii.stampii.comm.rpc;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.ResultSet;
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
*/
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,String keys,String value){
return execQuery(tableName,keys,value);
}
private static boolean execQuery(String tableName,String key,String value){
sqliteDb = instance.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(key, value);
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 = "code_id=?";
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 = "code_id=?";
sqliteDb.delete(tableName, where, new String[] {"5"});
return true;
}
public Cursor executeSQLQuery(String query){
return sqliteDb.rawQuery(query,null);
}
}
我的问题是:我怎样才能只初始化一次数据库并且可以从我的所有活动中访问它?(提示:我的资产文件夹中有 sqlite 文件，当应用程序启动时，我会将其复制到系统数据库文件夹中.)
My question is : How can I initialize the database only once and can access it from all my Activities? (Hint: I have sqlite files in my assets folder,which I copy to my system database folder when the app stars.)
提前致谢！
我忘了说我的应用程序中有 2 个不同的 sqlite 数据库，我希望能够为整个应用程序初始化它们并可以使用它们.这就是我正在尝试做:
EDIT : I forgot to say that I have 2 different sqlite databases in my application and I want to be able to initialize both of them for the whole application and can use them.That's something that I was trying to do :
DataBaseHelper dbHelper;
//some code
dbHelper = new DataBaseHelper(context, "ops_sys_tpl.sqlite", null, 1);
DataBaseHelper.initialize(context, "stampii_sys_tpl.sqlite");
dbHelper.copyDataBase("ops_sys_tpl.sqlite");
dbHelper.getDatabase();
dbHelper.executeQuery("users", "objectId", "2");
dbHelper.executeQuery("users","serverName","stampii");
dbHelper.executeQuery("users", "objectId", "3");
dbHelper.executeQuery("users","serverName","stampii");
dbHelper.executeQuery("users", "objectId", "3");
推荐答案
像这样只创建一次实例，您可以在 DB 处理程序类中添加相同的代码，但我更喜欢将其分开.
Create your instance only once like this, The same code you can add in DB handler class but I prefer to keep it seperate.
public class MyTestDatabaseInstanceHolder {
public MyTestDBHandler DBHelper;
public static SQLiteDatabase m_ObjDataBase; // This is global variable to access across the applicaiton
public static void createDBInstance(Context pContext){
if(DBHelper == null) {
DBHelper = new WLDBHandler(pContext); // This will be your DB Handler Class
m_cObjDataBase = DBHelper.openAndCreateDataBase(); // Initialze the DB Note: openAndCreateDataBase is a utility method created by you to do everything an return the DB object
}
}
}
在您的入口点(启动画面)中调用:
In your entry point (Splash Screen) call this:
MyTestDatabaseInstanceHolder.createDBInstance(getApplicationContext());
用法 - 其他一些类:
Usage - Some other Class:
MyTestDatabaseInstanceHolder.m_ObjDataBase.rawQuery(---);
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