Android: Cannot perform this operation because the connection pool has been closed

Question 1

Remove

db.close();

If you try another operation after closing the database, it will give you that exception.

The documentation says:

Releases a reference to the object, closing the object...

Also, check out Android SQLite closed exception about a comment from an Android Framework engineer which states that it is not necessary to close the database connection, however this is only when it is managed in a ContentProvider.

Question 2

I currently have the same problem. While removing the db.close() solves the issue for me, I think the issue is caused by multi-threading. Here is my research.

SQLiteOpenHelper holds a reference to SQLiteDatabase, when getReadableDatabase() or getWritableDatabase() called, it will return the reference, if the SQLiteDatabase is closed or null, a new SQLiteDatabase object will be created. Note that inside the get method, codes are guarded in a synchronized block.

SQLiteDatabase is a subclass of SQLiteClosable. SQLiteClosable implements a reference counting scheme.

When first created, the count is 1.
When the database operation methods run (like insert, query), it will increase the count, and decrease the count when methods end. But the cursor operations are NOT protected by reference counting.
If the count decreases to 0, connection pool will be closed and a member SQLiteConnectionPool object will be set to null, and now the SQLiteDatabase is closed;
SQLiteDatabase.close() will decrease the count by 1;

So, if you have a single-threaded scheme, closing the SQLiteDatabase will be fine because SQLiteOpenHelper will just re-recreate it.

If you do multi-threading, then you will run into trouble. Say thread A and thread B both call getReadableDatabase(), and SQLiteOpenHelper returns the SQLiteDatabase it holds, and then thread A first finished its operation and call SQLiteDatabase.close(), now the SQLiteDatabase object thread B has is closed so any subsequent db operation calls or cursor method calls will throw the exception.

Question 3

This is a simple error in Android architecture initialisation of room database with getApplicationContext(), this means that your application has one instance of the database reference, no matter how many activities create an instance of it, therefore if you close it in any activity the others will throw that exception.

Essentially don't just check the activity throwing the exception but every activity for db.close()

Question 4

I am having the same problem, have not been able to fix it. I have found a possible clue: I have a sync thread that is running all the time:

    Item ii = dbHelper.popPendingUpload();
    if (ii != null)
            upload(ii);

And inside DBHelper

public Item popPendingUpload() {

    SQLiteDatabase db = getReadableDatabase();
    Cursor res = db
            .rawQuery("SELECT * FROM items WHERE state = 0 LIMIT 1",
                    new String[] {});
    boolean hasNext = res.moveToFirst();
    Item ii = null;
    if (hasNext) {
        ii = //load item
    }
    db.close();
    return ii;
}

The error also shows up in the moveToFirst() method call. As the thread is poping items out in an infinite loop, the first time it works ok, the second time the error appears. The interesting part is that if I put a breakpoint and step through the code, the error does not show any more. I am testing on a real device using Android 4.1.

I know, is not an answer, but it may help. I'll keep on testing.

Question 5

//close database after cursor is closed like:

if(cursor.getCount() != 0){

    while(cursor.moveToNext()){
      //do operation
    }
}

cursor.close();
database.close();

Question 6

Maybe you close the database before access to database from your app.

You have to edit getProfile() to

public Profile getProfile(long id) {
  SQLiteDatabase db = this.getReadableDatabase();

  try {
    String selectQuery = "SELECT * FROM " + TABLE_PROFILES + " WHERE " + KEY_PROFILES_ID + " = " + id;
    Cursor cursor = db.rawQuery(selectQuery, null);

    // looping through all rows and adding to list
    Profile profile = new Profile();
    if (cursor.moveToFirst()) {
      doWhatEver();
    }
    cursor.close();
  finally {
    db.close();
  }
  return profile;
}

Question 7

I have a error like yours ,here my code:

  try {
                        String sql = "SELECT * FROM "+DB_TABLEDOWNLOAD;
                        Cursor cursor = db.rawQuery(sql, null);
                        //空双引号为原表没有的字段
                        String temp = "";
                        int existIconPath = cursor.getColumnIndex("iconPath");
                        int existAudioID = cursor.getColumnIndex("audioID");

                        if (existIconPath == -1 && existAudioID == -1){
                            temp = "url, downed,total,path,name, audioTitle, audioFileID,\"\",\"\"";
                        }else if (existIconPath == -1 && existAudioID != -1){//iconPath不存在
                            temp = "url, downed,total,path,name, audioTitle, audioFileID,\"\",audioID";
                        }else if (existIconPath != -1 && existAudioID == -1){//audioID不存在
                            temp = "url, downed,total,path,name, audioTitle, audioFileID,iconPath,\"\"";
                        }else {
                            return;
                        }

                        db.beginTransaction();
                        String tempTableName = "_temp_"+DB_TABLEDOWNLOAD;
                        String sqlCreateTemp = " ALTER TABLE "+DB_TABLEDOWNLOAD+" RENAME TO "+tempTableName+";";
                        db.execSQL(sqlCreateTemp);

                        final String TB_TESTPAPERINFO_CREATE = "Create  TABLE IF NOT EXISTS "
                                + DB_TABLEDOWNLOAD
                                + "(url TEXT, downed TEXT,total TEXT,path TEXT,name TEXT, audioTitle TEXT, audioFileID TEXT,iconPath TEXT, audioID TEXT);";
                        db.execSQL(TB_TESTPAPERINFO_CREATE);

                        String sqlBackupData = "INSERT INTO "+DB_TABLEDOWNLOAD+" SELECT "+temp+" FROM "+tempTableName+";";
                        db.execSQL(sqlBackupData);
                        String sqlDrop = "DROP TABLE IF EXISTS '"+tempTableName+"';";
                        db.execSQL(sqlDrop);
                        db.setTransactionSuccessful();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }finally{
                        db.endTransaction();
                    }

I use return before db.beginTransaction(),my code return before beginTransaction,but I endTransaction in finally . if you do not beginTransaction and endTransaction ,the exception will appear.

so check your code about the db.beginTransaction and endTransaction.

Question 8

Just to mention one more possibility to get this error in case someone searching this post run into the same case:

Using Database Inspector in Android Studio may cause this error in some situation.

Question 9

I got a similar error message and solved it by removing a db.close() in another activity.

I had a background process for population of a virtual table in one activity and then a db.close() in another activity.

The db.close() didn't do any harm before my long background process ran.