如何从Android中的助手类初始化sqlite数据库一次
内容导读
互联网集市收集整理的这篇技术教程文章主要介绍了如何从Android中的助手类初始化sqlite数据库一次,小编现在分享给大家,供广大互联网技能从业者学习和参考。文章包含8738字,纯文字阅读大概需要13分钟。
内容图文
![如何从Android中的助手类初始化sqlite数据库一次](/upload/InfoBanner/zyjiaocheng/892/3448cc838f1a432c8fccb37c027bb35c.jpg)
我有一个自定义的DataBaseHelper类,它扩展了SQLiteOpenHelper,如下所示:
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:如何只初始化数据库一次,并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,当应用程序出星时,我将其复制到我的系统数据库文件夹中.)
提前致谢!
编辑:我忘了说我的应用程序中有两个不同的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.这是我试图做的事情:
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");
解决方法:
像这样只创建一次你的实例,你可以在DB处理程序类中添加相同的代码,但我更喜欢将它保持独立.
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:
MyTestDatabaseInstanceHolder.createDBInstance(getApplicationContext());
用法 – 其他一些类:
MyTestDatabaseInstanceHolder.m_ObjDataBase.rawQuery(---);
内容总结
以上是互联网集市为您收集整理的如何从Android中的助手类初始化sqlite数据库一次全部内容,希望文章能够帮你解决如何从Android中的助手类初始化sqlite数据库一次所遇到的程序开发问题。 如果觉得互联网集市技术教程内容还不错,欢迎将互联网集市网站推荐给程序员好友。
内容备注
版权声明:本文内容由互联网用户自发贡献,该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容, 请发送邮件至 gblab@vip.qq.com 举报,一经查实,本站将立刻删除。
内容手机端
扫描二维码推送至手机访问。