Эй, я хочу прочитать из своей базы данных, поэтому я использовал этот класс, чтобы он копировал мою базу данных туда, где она должна быть, а затем, когда я пытаюсь выполнить запрос, происходит сбой:
public class DataBaseHelper extends SQLiteOpenHelper{
//The Androids default system path of your application database.
private static String DB_PATH = "/data/data/omar.gestore/databases/";
private static String DB_NAME = "test1.db";
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) {
}
public Cursor myQuery(String mquery){
try
{
Cursor c =myDataBase.rawQuery(mquery,null);
return c;
}
catch(Exception x)
{
return null;
}
// 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.
}
}
и в моем основном классе:
DataBaseHelper myDatabase=new DataBaseHelper(this);
try {
myDatabase.createDataBase();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
myDatabase.myQuery("SELECT * FROM adab;");
но он вылетает из-за нулевого указателя .. Кто-нибудь может сказать мне, почему? Спасибо.
EDIT1: сбой находится в этой строке: Cursor c = myDataBase.rawQuery (mquery, null); в функции myQuery