问在db助手的插入方法中关闭db是个好主意吗？

EN

 public class DbHelper extends SQLiteOpenHelper{

private SQLiteDatabase db;

public DbHelper(Context context) {
    super(context, "shareholders.db", null, 1);
}

@Override
public void onCreate(SQLiteDatabase db) {
    try {
        this.db = db;
        String sql = "CREATE TABLE IF NOT EXISTS news (id integer,title text,description text,sDate text)";
        db.execSQL(sql);


    } catch (Exception e) {
        xLog.error(e.getMessage());
    }


    ContentValues cv = new ContentValues();
    cv.put("name", "Username");
    cv.put("value", "default");
    db.insert("settings", null, cv);

    cv.clear();
    cv.put("name", "Password");
    cv.put("value", "default");
    db.insert("settings", null, cv);

    cv.clear();
    cv.put("name", "PersonId");
    cv.put("value", "default");
    db.insert("settings", null, cv);

    cv.clear();
    cv.put("name", "picture");
    cv.put("value", "");
    db.insert("settings", null, cv);
}

@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
    // TODO Auto-generated method stub

}

public long insert(String table,ContentValues cv){
    SQLiteDatabase mydb =this.getWritableDatabase();
    long result=-1;
    try {
        result = mydb.insert(table,null, cv);
        }catch (Exception e) {
        xLog.error(e.getMessage());
    }
    this.close();
    return result;
}

public Cursor selectAll(String table){
    SQLiteDatabase mydb =this.getReadableDatabase();
    String sql = "SELECT * FROM "+table;
    xLog.info(sql);
    Cursor result=null;
    try {
        result = mydb.rawQuery(sql, null);
    } catch (Exception e) {
        xLog.error(e.getMessage());
    }
    this.close();
    return result;
}

public Cursor select(String table,String where){
    SQLiteDatabase mydb =this.getReadableDatabase();
    String sql = "SELECT * FROM "+table+" WHERE "+where;
    xLog.info(sql);

    Cursor result=null;
    try {
        result = mydb.rawQuery("SELECT * FROM "+table+" WHERE "+where, null);
    } catch (Exception e) {
        xLog.error(e.getMessage());
    }
    this.close();
    return result;
}

public long delete(String table,String condition){
    SQLiteDatabase mydb =this.getWritableDatabase();
    long result = -1;
    try {
        result = mydb.delete(table, condition, null);
    } catch (Exception e) {
        xLog.error(e.getMessage());
    }
    this.close();
    return result;
}

protected long empty(String table){
    SQLiteDatabase mydb =this.getWritableDatabase();
    long result = -1;
    try {
        result = mydb.delete(table, "", null);
    } catch (Exception e) {
        xLog.error(e.getMessage());
    }
    this.close();
    return result;
}

public long update(String table,ContentValues cv,String condition){
    SQLiteDatabase mydb =this.getWritableDatabase();
    long result = -1;
    try {
        result = mydb.update(table, cv, condition, null);
    } catch (Exception e) {
        xLog.error(e.getMessage());
    }
    this.close();
    return result;
}

protected void drop(String table){
    //TODO Produces a damn error!
    db.execSQL("DROP TABLE IF EXISTS "+table);
}

11-26 13:12:20.738: W/System.err(2238): org.xmlpull.v1.XmlPullParserException: unexpected type (position:END_DOCUMENT null@1:0 in java.io.InputStreamReader@43e80ca8) 
11-26 13:12:20.738: W/System.err(2238):     at org.kxml2.io.KXmlParser.exception(KXmlParser.java:273)
11-26 13:12:20.738: W/System.err(2238):     at org.kxml2.io.KXmlParser.nextTag(KXmlParser.java:1420)
11-26 13:12:20.738: W/System.err(2238):     at org.ksoap2.SoapEnvelope.parse(SoapEnvelope.java:126)
11-26 13:12:20.738: W/System.err(2238):     at org.ksoap2.transport.Transport.parseResponse(Transport.java:96)
11-26 13:12:20.738: W/System.err(2238):     at org.ksoap2.transport.HttpTransportSE.call(HttpTransportSE.java:189)
11-26 13:12:20.745: W/System.err(2238):     at org.ksoap2.transport.HttpTransportSE.call(HttpTransportSE.java:95)
11-26 13:12:20.745: W/System.err(2238):     at ClassLibrary.WebService.CallMethod(WebService.java:49)
11-26 13:12:20.745: W/System.err(2238):     at ClassLibrary.AsyncCallWs.doInBackground(AsyncCallWs.java:64)
11-26 13:12:20.745: W/System.err(2238):     at ClassLibrary.AsyncCallWs.doInBackground(AsyncCallWs.java:1)
11-26 13:12:20.745: W/System.err(2238):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
11-26 13:12:20.745: W/System.err(2238):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
11-26 13:12:20.745: W/System.err(2238):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
11-26 13:12:20.745: W/System.err(2238):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
11-26 13:12:20.745: W/System.err(2238):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
11-26 13:12:20.745: W/System.err(2238):     at java.lang.Thread.run(Thread.java:1096)