我知道有数十亿个关于 SQL 数据库的线程，但我没有找到任何解决我的问题的方法。我制作了一个名为Beer Or No Beer的应用程序，它需要一个包含啤酒品牌及其所在国家/地区的 Arraylist。现在我想用 SQLite 管理这个列表。我用 SQLite 数据库浏览器创建了一个数据库，并将数据库复制到资产文件夹（名称：sqbeerlist）中。现在我创建了一个 DatabaseHelper 类来打开文件并将其写入数组列表。但是当我想用
Cursor c = myDataBase.rawQuery("SELECT _id, brand FROM " + DATABASE_TABLE, null);
DVM 崩溃并显示 Source Not Found。我究竟做错了什么 ？？
这是整个 HelperClass：
package com.celticwolf.alex;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class DataBaseHelper extends SQLiteOpenHelper {
// The Androids default system path of your application database.
private static String DB_PATH = "/data/data/com.celticwolf.alex/databases/";
private static String DB_NAME = "sqbeerlist";
private static final String DATABASE_TABLE = "beers";
private SQLiteDatabase myDataBase;
public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "brand";
public static final String KEY_COUNTRY = "country";
private final Context myContext;
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 doesnt
*/
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 doest 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();
}
public ArrayList<String> gettheArray() {
ArrayList<String> result = new ArrayList<String>();
try {
openDataBase();
}catch(SQLException sqle){
throw sqle;
}
Cursor c = myDataBase.rawQuery("SELECT _id, brand FROM " + DATABASE_TABLE, null);
c.moveToFirst();
// Check if our result was valid.
if (c != null) {
// Loop through all Results
do {
result.add(c.getString(c.getColumnIndex(KEY_NAME)));
} while (c.moveToNext());
}
close();
return result;
}
@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.
}
这是我访问课程的方式：
DataBaseHelper myDbHelper = new DataBaseHelper(null);
myDbHelper = new DataBaseHelper(this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
ArrayList<String> thelist = myDbHelper.gettheArray();
谢谢，我希望有人可以提供帮助（：
问题解决了！ 这是正确的代码！这个标志标志着变化：c==3
package com.celticwolf.alex;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
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.celticwolf.alex/databases/";
private static String DB_NAME = "sqbeerlist.sqlite";
private static final String DATABASE_TABLE = "beers";
private SQLiteDatabase myDataBase;
public static final String KEY_ROWID = "_id";
public static final String KEY_NAME = "brand";
public static final String KEY_COUNTRY = "country";
private final Context myContext;
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();
SQLiteDatabase db_Read = null; // c==3
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.
db_Read = this.getReadableDatabase(); // c==3
db_Read.close(); // c==3
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 doesnt
*/
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
(SQLiteDatabase.OPEN_READONLY | SQLiteDatabase.NO_LOCALIZED_COLLATORS)); // c==3
} catch (SQLiteException e) {
// database doesnt 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 | SQLiteDatabase.NO_LOCALIZED_COLLATORS)); // c==3
}
@Override
public synchronized void close() {
if (myDataBase != null)
myDataBase.close();
super.close();
}
public ArrayList<String> gettheArray() {
ArrayList<String> result = new ArrayList<String>();
try {
openDataBase();
}catch(SQLException sqle){
throw sqle;
}
Cursor c = myDataBase.rawQuery("SELECT _id, brand FROM " + DATABASE_TABLE, null);
c.moveToFirst();
// Check if our result was valid.
if (c != null) {
// Loop through all Results
do {
result.add(c.getString(c.getColumnIndex(KEY_NAME)));
} while (c.moveToNext());
}
close();
return result;
}
@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 itd
// be easy
// to you to create adapters for your views.
}