获取＆＃34;连接池已关闭＆＃34;错误

Question

我使用Singleton Approach创建了DBhandler，其中数据库的1个对象一次可用于任何事务。

在从Asynctask的doInBackground方法中获取数据库中的数据时，我得到了连接池问题SOMETIMES。 在这里，我附上了我的代码片段。请澄清我在哪里做错了：

DBHandler中的方法

public List<MIC_OrderDetails> getdata(String Loc) {

        Cursor cursor = null;
        List<MIC_OrderDetails> ordlst = new ArrayList<MIC_OrderDetails>();
        SQLiteDatabase db = getReadableDatabase();

        String q = "SELECT * FROM " + DatabaseHandler.TABLE_MIC2
                + " WHERE Location ='" + Loc + "'";

        cursor = db.rawQuery(q, null);

        try {
            while (cursor.moveToNext()) {
                MIC_OrderDetails mic_OrderDetails = new MIC_OrderDetails();

                mic_OrderDetails.setItemNumber(cursor.getString(2));
                mic_OrderDetails.setItemDescription(cursor.getString(3));
                mic_OrderDetails.setPickSeq(cursor.getString(4));
                mic_OrderDetails.setQtyonHand(cursor.getDouble(5)+"");
                mic_OrderDetails.setQtyCount(cursor.getDouble(6)+"");
                mic_OrderDetails.setUnit(cursor.getString(7));

                ordlst.add(mic_OrderDetails);
            }

        } catch (Exception e) {
            e.printStackTrace();
            errCode = "Error 5210";
            msg = "MIC_OrderDetails failed.";
            errMsg = errCode + " : " + msg;
            LogfileCreator.appendLog(errMsg);
            db.close();
        } finally {
            if (cursor != null && !cursor.isClosed()) {
                cursor.close();
            }
        }

        return ordlst;

    }

从Databse获取数据：

@Override
        protected List<MIC_OrderDetails> doInBackground(String... params) {
            // TODO Auto-generated method stub
            String result = "";
            List<MIC_OrderDetails> lst = new ArrayList<MIC_OrderDetails>();
            try {

                dbhelper.getReadableDatabase();
                lst = dbhelper.getdata(spinLoc);
                dbhelper.close();

                result = "success";
                MIC_OrderDetails mic_OrderDetails = new MIC_OrderDetails();
                mic_OrderDetails.setResult(result);
                lst.add(mic_OrderDetails);

            }

            catch (Exception e) {
                result = "error";
                MIC_OrderDetails mic_OrderDetails = new MIC_OrderDetails();
                mic_OrderDetails.setResult(result);
                lst.add(mic_OrderDetails);
                dialog.dismiss();
                Log.e("Failed", e.getLocalizedMessage());
            }
            return lst;
        }

记录错误

07-04 12:45:45.466: W/System.err(26516): java.lang.IllegalStateException: Cannot perform this operation because the connection pool has been closed.
07-04 12:45:45.474: W/System.err(26516):    at android.database.sqlite.SQLiteConnectionPool.throwIfClosedLocked(SQLiteConnectionPool.java:972)
07-04 12:45:45.474: W/System.err(26516):    at android.database.sqlite.SQLiteConnectionPool.waitForConnection(SQLiteConnectionPool.java:609)
07-04 12:45:45.474: W/System.err(26516):    at android.database.sqlite.SQLiteConnectionPool.acquireConnection(SQLiteConnectionPool.java:349)
07-04 12:45:45.474: W/System.err(26516):    at android.database.sqlite.SQLiteSession.acquireConnection(SQLiteSession.java:894)
07-04 12:45:45.474: W/System.err(26516):    at android.database.sqlite.SQLiteSession.executeForCursorWindow(SQLiteSession.java:834)
07-04 12:45:45.474: W/System.err(26516):    at android.database.sqlite.SQLiteQuery.fillWindow(SQLiteQuery.java:62)
07-04 12:45:45.474: W/System.err(26516):    at android.database.sqlite.SQLiteCursor.fillWindow(SQLiteCursor.java:143)
07-04 12:45:45.474: W/System.err(26516):    at android.database.sqlite.SQLiteCursor.getCount(SQLiteCursor.java:133)
07-04 12:45:45.474: W/System.err(26516):    at android.database.AbstractCursor.moveToPosition(AbstractCursor.java:196)
07-04 12:45:45.474: W/System.err(26516):    at android.database.AbstractCursor.moveToNext(AbstractCursor.java:244)
07-04 12:45:45.474: W/System.err(26516):    at com.mis.database.DatabaseHandler.getdata(DatabaseHandler.java:1345)
07-04 12:45:45.474: W/System.err(26516):    at com.mis.controller.InventoryCount$InflateList.doInBackground(InventoryCount.java:4052)
07-04 12:45:45.474: W/System.err(26516):    at com.mis.controller.InventoryCount$InflateList.doInBackground(InventoryCount.java:1)
07-04 12:45:45.474: W/System.err(26516):    at android.os.AsyncTask$2.call(AsyncTask.java:287)
07-04 12:45:45.474: W/System.err(26516):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
07-04 12:45:45.474: W/System.err(26516):    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
07-04 12:45:45.474: W/System.err(26516):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
07-04 12:45:45.474: W/System.err(26516):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
07-04 12:45:45.474: W/System.err(26516):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
07-04 12:45:45.474: W/System.err(26516):    at java.lang.Thread.run(Thread.java:856)