【发布时间】：2014-04-14 19:45:43
【问题描述】：
我在 Android 应用程序的资产目录中添加了一个预先填充的数据库，但是当我删除并添加一个新数据库时，查询结果仍然返回旧数据。
我关注了这个tutorial，下面是我的数据库类：
package com.example.fishselector;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.HashMap;
import android.content.ContentValues;
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;
class DB extends SQLiteOpenHelper {
private static String DB_PATH = "/data/data/com.example.fishselector/databases/";
private static String DB_NAME = "sqldb3";
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 DB(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) {
try {
createDataBase();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
@
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.
}
【问题讨论】：
-
这看起来像你的
Activity类。无论如何，您肯定已经从 SD 卡中删除了 db？ -
如果数据库类中存在表，为什么不使用 SQLite 删除表？我认为这是 DROP TABLE IF EXISTS 'TABLE_NAME'
-
@KenWolf FML 我把主要活动 lol 修复了
-
@KenWolf 我实际上是在模拟器上测试它，只是从eclipse路径中的资产目录中删除它
-
你必须从文件系统中删除它，因为这就是它的工作原理。您不能直接从
assets访问数据库。您的代码将文件复制到/data/data/com.example.fishselector/databases/，然后从那里访问它。因此，当您从assets删除它并再次运行该应用程序时，什么也没有发生 - 它仍然在您最初复制它的路径中。