在同一數據庫上運行的不同線程中的多個遊標

Question

我在asynctask類doInBackground（）中初始化數據庫實例。數據庫實例及其方法位於一個單獨的類中（我將展示的那個類）從asynctask中，我爲Azure客戶端啓動另一個類的線程，最終查詢數據庫類來填充我的azure數據庫客戶端。回到我的asyncTask，我再次訪問數據庫（同時作爲第一個查詢）來查詢數據庫以獲取單獨的信息。似乎有兩個遊標同時從單獨的線程查詢正在導致我的問題。

下面是使用第一個遊標向Azure發送內容的db類中的方法。這些方法是從Azure類中運行的獨立線程調用的。 Azure類在asynctask類中調用。正如你將在logcat中看到的，這工作正常。

public ArrayList<WeatherEvent> GetUnsychedWeatherEvent() { 
    String query = COLUMN_SYNCHED + " = 0 "; 
    Cursor cursor = db.query(TABLE_WEATHER, null, query, null, null, null, null); 

    ArrayList<WeatherEvent> unsychedWeather = new ArrayList<>(); 
    while (cursor.moveToNext()) { 
     unsychedWeather.add(GetWeatherEvent(cursor)); 
    } 
    cursor.close(); 

    return unsychedWeather; 

} 

//get weather event from db for azure 
//TODO: finish populating this 
public WeatherEvent GetWeatherEvent(Cursor cursor) { 
    WeatherEvent wEvent = new WeatherEvent(); 
    wEvent.Latitude = cursor.getDouble(cursor.getColumnIndex(COLUMN_LATITUDE)); 
    wEvent.Longitude = cursor.getDouble(cursor.getColumnIndex(COLUMN_LONGITUDE)); 
    wEvent.CurrTemp = cursor.getString(cursor.getColumnIndex(COLUMN_CURRENT_TEMPERATURES)); 
    wEvent.CurrDesc = cursor.getString(cursor.getColumnIndex(COLUMN_CURRENT_WEATHER_DESCRIPTION)); 
    System.out.println("From DB, current temp: " + wEvent.CurrTemp); 
    try { 
     wEvent.Time = timeStampFormat.parseDateTime(cursor.getString(cursor.getColumnIndex(COLUMN_TIME_STAMP))); 
    } catch (Exception e) { 
     Log.d("GetEvent()", "Error parsing date " + e.toString()); 
    } 

    return wEvent; 
} 

這些下一個方法來自同一個db類。這裏的'每日一趟'是造成我麻煩的原因。這些方法在asynctask類中調用。

public ArrayList<WeatherEvent> DailyWeatherEvents(ArrayList<WeatherEvent> dailyWeatherEvents) { 
     Log.d("DB Access", "got to dailyweatherevents"); 

    //todo: more specific time query 
    Cursor dailycursor = db.rawQuery("SELECT avg(" + COLUMN_CURRENT_TEMPERATURES + "), " + COLUMN_TIME_STAMP + ", " + 
      "CASE WHEN strftime('%M', " + COLUMN_TIME_STAMP + ") < '30' " + 
      "THEN strftime('%H', " + COLUMN_TIME_STAMP + ") " + 
      "ELSE strftime('%H', " + COLUMN_TIME_STAMP + ", '+1 hours') END " + 
      "FROM " + TABLE_WEATHER + " "+ 
      "GROUP BY strftime('%H', " + COLUMN_TIME_STAMP + ", '+30 minutes')", null); 

    //ArrayList<WeatherEvent> dailyWeatherEvents = new ArrayList<>(); 
    try { 
     if (dailycursor.moveToFirst()) { 
      while (dailycursor.moveToNext()) { 
       dailyWeatherEvents.add(GetDailyWeatherEvent(dailycursor)); 

      } 
      dailycursor.close(); 
      System.out.println("Size of dailyinfo " + dailyWeatherEvents.size()); 
     } 
     } catch (Exception e) { 
     e.printStackTrace(); 
    } 
    return dailyWeatherEvents; 
} 

public WeatherEvent GetDailyWeatherEvent(Cursor dailycursor) { 
    WeatherEvent wEvent = new WeatherEvent(); 
    // wEvent.Latitude = dailycursor.getDouble(dailycursor.getColumnIndex(COLUMN_LATITUDE)); 
    // wEvent.Longitude = dailycursor.getDouble(dailycursor.getColumnIndex(COLUMN_LONGITUDE)); 
    wEvent.CurrTemp = dailycursor.getString(dailycursor.getColumnIndex(COLUMN_CURRENT_TEMPERATURES)); 
    System.out.println(wEvent.CurrTemp + " mariah this comes from cursor"); 
    wEvent.CurrDesc = dailycursor.getString(dailycursor.getColumnIndex(COLUMN_CURRENT_WEATHER_DESCRIPTION)); 
    try { 
     wEvent.Time = timeStampFormat.parseDateTime(dailycursor.getString(dailycursor.getColumnIndex(COLUMN_TIME_STAMP))); 
    } catch (Exception e) { 
     Log.d("GetEvent()", "Error parsing date " + e.toString()); 
    } 
    wEvent.CurrIcon = dailycursor.getString(dailycursor.getColumnIndex(COLUMN_CURRENT_ICONS)); 
    wEvent.SevereWeatherPresent = dailycursor.getInt(dailycursor.getColumnIndex(COLUMN_SEVERE_WEATHER_PRESENT))>0; 

    return wEvent; 

} 

從asynctask類開始的所有這些行。 WeatherDBAccess是數據庫類。該WeatherAzureAccess是蔚藍類：

WeatherDBAccess._context = this.context; 
      WeatherDBAccess.Instance().AddWeatherEvent(wEvent); 
      //starts azure 
      WeatherAzureAccess.context = this.context; 
      WeatherAzureAccess.Instance(); 


     //prep dailyinfo arraylist 

      dailyinfo = WeatherDBAccess.Instance().DailyWeatherEvents(dailyinfo); 

，這是我的logcat，「從DB，當前溫度：XX」的行會從方法打印爲天藍色：

01-12 15:15:43.869 29979-30189/pdgt.cat.com.noaahso I/SQLiteAssetHelper: successfully opened database HSO.sqlite 
01-12 15:15:43.869 29979-30189/pdgt.cat.com.noaahso D/WeatherDBAccess: Instance Created /data/data/pdgt.cat.com.noaahso/databases/HSO.sqlite 
01-12 15:15:43.869 29979-30189/pdgt.cat.com.noaahso I/System.out: Current Temp: 54 
01-12 15:15:43.899 29979-30189/pdgt.cat.com.noaahso I/System.out: Weather Event Added 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso D/DB Access: got to dailyweatherevents 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso E/CursorWindow: Failed to read row 1, column -1 from a CursorWindow which has 3 rows, 3 columns. 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err: java.lang.IllegalStateException: Couldn't read row 1, col -1 from CursorWindow. Make sure the Cursor is initialized correctly before accessing data from it. 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso D/AzureAccess: WeatherSync thread STARTED! 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at android.database.CursorWindow.nativeGetString(Native Method) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at android.database.CursorWindow.getString(CursorWindow.java:451) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at android.database.AbstractWindowedCursor.getString(AbstractWindowedCursor.java:51) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at pdgt.cat.com.noaahso.WeatherDBAccess.GetDailyWeatherEvent(WeatherDBAccess.java:235) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at pdgt.cat.com.noaahso.WeatherDBAccess.DailyWeatherEvents(WeatherDBAccess.java:219) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at pdgt.cat.com.noaahso.WeatherTask.doInBackground(WeatherTask.java:228) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at pdgt.cat.com.noaahso.WeatherTask.doInBackground(WeatherTask.java:47) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at android.os.AsyncTask$2.call(AsyncTask.java:288) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at java.util.concurrent.FutureTask.run(FutureTask.java:237) 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 49 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
01-12 15:15:43.919 29979-30189/pdgt.cat.com.noaahso W/System.err:  at java.lang.Thread.run(Thread.java:818) 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 49 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 49 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 49 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 50 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 50 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 50 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 51 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 51 
01-12 15:15:43.919 29979-29979/pdgt.cat.com.noaahso D/AsyncTask: got to onpostExecute 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 51 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 51 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 51 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 51 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 51 
01-12 15:15:43.919 29979-30298/pdgt.cat.com.noaahso I/System.out: From DB, current temp: 51 

我需要在第一個光標上使用FutureCallback來知道何時啓動第二個光標？還是我需要使我的第一個遊標全局，並等到第一個查詢完成之前我重置一個遊標做我的第二個查詢？尋找一個解決方案，我已經知道，開始第二個光標是昂貴的。我的問題是很少使用第二個遊標（可能只有onCreate（）），並且第一個遊標幾乎總是會繼續使用，因爲它始終用於將內容發送到Azure。也FYI我關閉我的數據庫onDestroy（）。

Answer 1

首先，你的錯誤是：

java.lang.IllegalStateException：無法從 CursorWindow讀取行1，列-1。確保光標在 從其訪問數據之前正確初始化。

這意味着，你有結果（第1行），但你正在嘗試讀取無效列索引（col -1）。

問題區域很可能在這裏：

wEvent.CurrTemp = dailycursor.getString(dailycursor.getColumnIndex(COLUMN_CURRENT_TEMPERATURES)); 

您從getColumnIndex因爲COLUMN_CURRENT_TEMPERATURES在您的SQL查詢不存在得到一個-1的結果。

Cursor dailycursor = db.rawQuery("SELECT avg(" + COLUMN_CURRENT_TEMPERATURES + "), " + COLUMN_TIME_STAMP + ", " + 
      "CASE WHEN strftime('%M', " + COLUMN_TIME_STAMP + ") < '30' " + 
      "THEN strftime('%H', " + COLUMN_TIME_STAMP + ") " + 
      "ELSE strftime('%H', " + COLUMN_TIME_STAMP + ", '+1 hours') END " + 
      "FROM " + TABLE_WEATHER + " "+ 
      "GROUP BY strftime('%H', " + COLUMN_TIME_STAMP + ", '+30 minutes')", null); 

您需要包括你意圖從你的SELECT語句讀取的所有列：

Cursor dailycursor = db.rawQuery("SELECT avg(" + COLUMN_CURRENT_TEMPERATURES + "), " + COLUMN_CURRENT_TEMPERATURES + ", " + COLUMN_CURRENT_WEATHER_DESCRIPTION + ", " + COLUMN_CURRENT_ICONS + ", " + COLUMN_SEVERE_WEATHER_PRESENT + ", " + COLUMN_TIME_STAMP + ", " + 
      "CASE WHEN strftime('%M', " + COLUMN_TIME_STAMP + ") < '30' " + 
      "THEN strftime('%H', " + COLUMN_TIME_STAMP + ") " + 
      "ELSE strftime('%H', " + COLUMN_TIME_STAMP + ", '+1 hours') END " + 
      "FROM " + TABLE_WEATHER + " "+ 
      "GROUP BY strftime('%H', " + COLUMN_TIME_STAMP + ", '+30 minutes')", null);