如何访问和查询被复制到文件夹资产数据库？ [英] How to access and query the database that is copied to the assets folder?
问题描述
我看过一些教程，其中以pre-现有的数据库复制到资产的文件夹，并写入$ C $下对应用程序数据库的默认系统路径复制这个数据库。
I have read few tutorials where in a pre-existing database is copied to assets folder and write code for copying this database on to the default system path of the application database.
package com.example.c1;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class DataBaseHelper extends SQLiteOpenHelper {
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.example.c/databases/";
private static String DB_NAME = "MyDatabase";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DataBaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}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.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* 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;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* 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() 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 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();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
// Add your public helper methods to access and get content from the database.
// You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
// to you to create adapters for your views.
}
我用这个code复制数据库从Assets文件夹默认路径。
I use this code for copying the database from assets folder to default path.
package com.example.c1;
import java.io.IOException;
import com.example.c1.DataBaseHelper;
import android.os.Bundle;
import android.app.Activity;
import android.database.SQLException;
import android.view.Menu;
import android.widget.TextView;
public class C1 extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.c1);
DataBaseHelper myDbHelper = new DataBaseHelper(this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
}catch(SQLException sqle){
throw sqle;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.c1, menu);
return true;
}
}
运行这个，模拟器说，C1已经停止。我点击DDMS视图和文件浏览器选择我的包。我找到了数据库文件夹中。我的资产文件夹，即数据库; MyDatabase的在这里找到。但是，当我拉的文件，并在源码浏览器中打开它只能说明android_metadata表，但不显示在我的数据库其他表。我也不能执行任何查询。如何访问和查询数据库？像DataBaseHelper类执行选择的声明，并呈现出它的结果。我希望我清楚我的问题。我复制到资产的文件夹和code这个数据库复制到默认路径的数据库。是code正确吗？如果没有，那么什么是修正我应该做？我需要执行查询作如何做到这一点？
Running this, the emulator says c1 has stopped. I click on the DDMS view and in file explorer I choose my package. I found "databases" folder. My database in the assets folder ie; "MyDatabase" is found here. But when I pull the file and open it in sqlite browser it only shows the android_metadata table but doesn't show other tables in my database. I am also not able to execute any query. How can I access and query the database? like executing a "Select" statement in DataBaseHelper class and showing the result of it. I hope am clear with my problem. I have a database copied on to assets folder and a code to copy this database to the default path. Is the code correct? If not then what is the correction I should make? I need to execute query n how to do it??
推荐答案
您需要将数据库文件复制到应用程序目录的文件夹，然后使用这个文件来打开数据库
You need to copy your database file to application directory folder then use this file to open database
我用这个来copyDatabase
I use this to copyDatabase
private void copyDataBase()
{
Log.i("Database", "New database is being copied to device!");
byte[] buffer = new byte[1024];
OutputStream myOutput = null;
int length;
// Open your local db as the input stream
InputStream myInput = null;
try
{
myInput = myContext.getAssets().open(DB_NAME);
// transfer bytes from the inputfile to the
// outputfile
myOutput = new FileOutputStream(DB_PATH + DB_NAME);
while((length = myInput.read(buffer)) > 0)
{
myOutput.write(buffer, 0, length);
}
myOutput.close();
myOutput.flush();
myInput.close();
Log.i("Database", "New database has been copied to device!");
cmn.mailDetails();
}
catch(IOException e)
{
e.printStackTrace();
}
}
和
打开使用此
protected Boolean openDatabase()
{
if(isDatabaseExist(false))
{
// Open the database
String myPath = DB_PATH + DB_NAME;
try
{
Log.i("Database", "Trying to Open Database!");
if(myDataBase != null)
{
if(!myDataBase.isOpen())
{
Log.i("Database", "Database is closed now opening it!");
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
}
else
{
Log.i("Database", "Database is already Open!");
}
Log.i("Database", "Database is Opened successfully in OPEN_READWRITE Mode !");
return true;
}
else
{
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
Log.i("Database", "Database is Opened successfully in OPEN_READWRITE Mode !");
return true;
}
}
catch(Exception e)
{
Log.e("Database", "Some error occured while opening Database Error:" + e.getMessage());
myDataBase = null;
return false;
}
}
else
{
copyDataBase();
}
return false;
}
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