我是java和android的初学者。现在我想使用外部数据库（cancer.db）。 我创建了＆＃34; DataBaseHelper＆＃34;类。
public class DataBaseHelper extends SQLiteOpenHelper{
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/YOUR_PACKAGE/databases/";
private static String DB_NAME = "myDBName";
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;
}
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.}
然后我使用下面的代码＆＃34;在创建＆＃34;创建或打开数据库的方法：
private static String DB_PATH = "/data/data/info.myprogram/databases/";
private static String DB_NAME = "cancer.db";
DataBaseHelper myDbHelper = new 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;
}
我使用这些代码来获取查询。我的表名是＆＃34; shb＆＃34;：
SQLiteDatabase db;
Cursor cc= db.rawQuery("SELECT Name FROM shb WHERE _id=1",null);
cc.moveToFirst();
String sss=cc.getString(1);
现在当我开始调试时，我得到了错误。错误的代码是什么？我的错是什么？我应该如何获得查询？ 请原谅我的英语不好，因为这不是我的母语。
答案 0 :(得分：-1)
首先创建一个sqlite数据库并在其中创建表，将其放在app的assets文件夹中。使用以下代码使用该数据库。请更改datbaseName，tableName，fieldsName和数据库路径等的代码。我还通过传递paerticuler值来编写获取数据列表的代码。
public class MySQLiteHelper extends SQLiteOpenHelper {
public static final String TABLE_CARS = "Cars";
public static final String COL_ENAME = "ename";
public static final String COL_MODAL = "modal";
public static final String COL_ANAME = "aname";
public static final String COL_TYPES = "types";
private static final String TAG = "MSSS : DatabaseHelper";
// Your Database Name
private static final String DATABASE_NAME = "4saleCars.sqlite";
// Your Your Database Version
private static final int DATABASE_VERSION = 1;
private final Context myContext;
private SQLiteDatabase myDataBase;
// The Android's default system path of your application database. DB_PATH =
// "/data/data/YOUR_PACKAGE/databases/"
private String DB_PATH = "/data/data/net.forsalemall.android/databases/";
public MySQLiteHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.myContext = context;
try {
createDataBase();
} catch (Exception e) {
Log.e(TAG,
"DatabaseHelper_constuctor createDataBase :"
+ e.fillInStackTrace());
}
}
@Override
public void onCreate(SQLiteDatabase database) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
// ***************************** My DB Handler Methods
// *****************************
/**
* Creates a empty database on the system and rewrites it with your own
* database.
**/
public void createDataBase() throws IOException {
boolean dbExist = checkDataBase();
if (dbExist) {
// Database already exist
openDataBase();
} 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.
myDataBase = getWritableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error createDataBase().");
}
}
}
/**
* 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 + DATABASE_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
} catch (SQLiteException e) {
// database does't exist yet.
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
/*
* public boolean isDataBaseExist() { File dbFile = new File(DB_PATH +
* DATABASE_NAME); return dbFile.exists(); }
*/
/**
* 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 transferring bytestream.
**/
private void copyDataBase() throws IOException {
try {
// Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DATABASE_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DATABASE_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();
} catch (IOException e) {
throw new Error("Error copyDataBase().");
}
}
public void openDataBase() throws SQLException, IOException {
try {
// Open the database
String myPath = DB_PATH + DATABASE_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null,
SQLiteDatabase.OPEN_READWRITE);
} catch (SQLiteException e) {
throw new Error("Error openDataBase().");
}
}
// ***************************** My DML Methods
// *****************************
public List<String> getModalList(String aname, Context context) {
List<String> list = new ArrayList<String>();
list.add(context.getResources().getString(R.string.all));
Cursor cursor;
String query;
query = "SELECT modal FROM Cars WHERE aname = '" + aname + "';";
try {
cursor = myDataBase.rawQuery(query, null);
if (cursor != null) {
while (cursor.moveToNext())
list.add(Utils.getDecodedString(cursor.getString(0)));
}
cursor.deactivate();
} catch (Exception e) {
Log.e(TAG, "getModalList Error : " + e.fillInStackTrace());
}
return list;
}
}
在您的活动中使用此 getModalList ，如下所示
MySQLiteHelper dbHelper = new MySQLiteHelper(
AdvanceSearchActivity.this);
String aname = Utils.getEncodedString(catName);
car_modal = dbHelper.getModalList(aname,AdvanceSearchActivity.this);