SQLite database never close in my Android app

问题

I have a problem with my Android application. I'm using code bellow to opening SQLite database in AsyncTask. Everything works fine but when I try to close database in onStop() or onDestroy method, it's never closed.

Code for creating and opening database:

public class SQLiteDB extends SQLiteOpenHelper{

private final Context context;  
private SQLiteDatabase sqliteDatabase = null;

public SQLiteDB(Context context, String DBName) {
    super(context, DBConstant.DB_NAME, null, context.getResources().getInteger(ppredota.android.navigation.view.activities.R.string.database_version));
    this.context = context;
}

public void createDB() throws IOException{


    if(existDB()){
        this.getReadableDatabase();
        this.close();
    }
    else {
        this.getWritableDatabase();
        try {
            copyDB();
            this.close();   
        }
        catch (Exception e) {
            throw new Error("Chyba pri kopirovani databaze");
        }
    }
}
private boolean existDB() {

    SQLiteDatabase checkDatabase = null;

    try{
        String fullPath = DBConstant.DB_PATH + DBConstant.DB_NAME;
        checkDatabase = SQLiteDatabase.openDatabase(fullPath, null, SQLiteDatabase.OPEN_READWRITE);
    }
    catch (SQLiteException sqle) {
        Log.i("existDB()", "Databaze nelze otevrit, neexistuje");
    }
    if(checkDatabase == null){
        Log.i("existDB", "Databaze jeste neexistuje...");
        return false;
    }
    else{
        Log.i("existDB", "Databaze uz existuje...");
        checkDatabase.close();
        return true;
    }

}

private void copyDB() throws IOException {

    InputStream inDBStream = context.getAssets().open(DBConstant.DB_NAME);
    String newDBPath = DBConstant.DB_PATH + DBConstant.DB_NAME;

    OutputStream outDBStream = new FileOutputStream(newDBPath);
    Log.i("copyDB", "Otevren outputstream s cestou k nove databazi");

    byte[] buffer = new byte[1024];
    int length;
    while ((length = inDBStream.read(buffer))>0){
        outDBStream.write(buffer, 0, length);
    }

    outDBStream.flush();
    outDBStream.close();
    inDBStream.close();
}

public void openDB() throws SQLException {
    String fullPath = DBConstant.DB_PATH + DBConstant.DB_NAME;
    if(sqliteDatabase!=null){
        if(sqliteDatabase.isOpen()){
            Log.i("openDB()", "Databaze je jiz otevrena");
        }
        else{
            sqliteDatabase = SQLiteDatabase.openDatabase(fullPath, null, SQLiteDatabase.OPEN_READONLY);
            Log.i("openDB()", "Databaze" + sqliteDatabase.getPath() + "otevrena");
        }
    }
    else{
        sqliteDatabase = SQLiteDatabase.openDatabase(fullPath, null, SQLiteDatabase.OPEN_READONLY);
        if(sqliteDatabase.isOpen()){
            Log.i("openDB()", "Databaze otevrena");
        }

    }
}
@Override
public void close() {

    if(sqliteDatabase!=null){
        sqliteDatabase.close();
        Log.i("close()", "Databaze zavrena");
    }
    super.close();

}

public SQLiteDatabase getSQLiteDatabase() {
    if(sqliteDatabase==null){
        Log.i("getSQLiteDatabase()","Problem, vraci sqliteDatabase = null");
    }
    else{
        Log.i("getSQLiteDatabase()","instance sqliteDatabase vracena bez problemu");
    }

    return sqliteDatabase;

}

AssyncTask class:

public class OpenDatabaseTask extends AsyncTask {

private Context context;
private SQLiteDB sqliteDB;

public OpenDatabaseTask(Context context,SQLiteDB sqliteDB) {
    this.context = context;
    this.sqliteDB = sqliteDB;
}
@Override
protected Void doInBackground(Void... params) {
    publishProgress();

    try {
        sqliteDB.createDB();
    } catch (IOException e) {
        e.printStackTrace();
    }
    sqliteDB.openDB();

    return null;
}
@Override
protected void onProgressUpdate(Void...unused){
    Log.i(OpenDatabaseTask.class.toString(), "Spusteno vlakno");
}

}

and Activity (only important part):

    private SQLiteDB sqliteDB;
    private SQLiteData sqliteData;
    private OpenDatabaseTask openDatabaseTask;

 @Override
 public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.navigatemenu);

        sqliteDB = new SQLiteDB(getApplicationContext(), sourceDatabaseName);
        openDatabaseTask = new OpenDatabaseTask(getApplicationContext(), sqliteDB);
        openDatabaseTask.execute();

    protected void onDestroy(){
        super.onDestroy();
        Log.i("onDestroy()", "Pokus o zavreni databaze");
            //here is the problem, database never closed
        sqliteDB.close();
    }
    protected void onStop(){
        super.onStop();
        Log.i("onStop()", "Pokus o zavreni databaze");
            //here is the problem, database never closed
        sqliteDB.close();
    }
    protected void onPause(){
        super.onPause();
    }
    protected void onResume(){
        super.onResume();
        //Log.i("onResume()", "Pokus o otevreni databaze");
    }
}

So when I try use a close() method to closing database, sqliteDatabase is always null and database is never closed. So database is still opened and after calling onDestroy exception occurs.

Thank you for your time and sorry for my english, I'm czech :)

回答1:

Just a guess (assuming you want to close on destroy)

close the database before calling the super

protected void onDestroy(){
    // close befor super is called
    sqliteDB.close();

    super.onDestroy();
    Log.i("onDestroy()", "Pokus o zavreni databaze");
    // sqliteDB.close(); // super.onDestroy may already has destroyed the DB
}

---

Note:

Assuming that the database only exists and is open while the activity is visible you should open the database in onResume() and close it in onPause().

If the database should be open when the code is loaded into memory create it in onCreate and close it in onDestroy

In your example you open it in onCreate and close it in onStop. Problem: when the activity becomes visible for the 2nd time the db is closed. For details see android activity documentation and look into the Application-Lifecycle at the button.

回答2:

I have an app with heavy db interaction. I didnt user helper. My db is opened lots of times, in UI thread and in background thread too, but never ever closed. Had no problems so far, dont know if it is the right way to do...

来源：https://stackoverflow.com/questions/9636880/sqlite-database-never-close-in-my-android-app