在同一数据库上运行的不同线程中的多个游标
我在asynctask类doInBackground()中初始化数据库实例。数据库实例及其方法位于一个单独的类中(我将展示的那个类)从asynctask中,我为Azure客户端启动另一个类的线程,最终查询数据库类来填充我的azure数据库客户端。回到我的asyncTask,我再次访问数据库(同时作为第一个查询)来查询数据库以获取单独的信息。似乎有两个游标同时从单独的线程查询正在导致我的问题。在同一数据库上运行的不同线程中的多个游标
下面是使用第一个游标向Azure发送内容的db类中的方法。这些方法是从Azure类中运行的独立线程调用的。 Azure类在asynctask类中调用。正如你将在logcat中看到的,这工作正常。
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;
}
这些下一个方法来自同一个db类。这里的'每日一趟'是造成我麻烦的原因。这些方法在asynctask类中调用。
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;
}
从asynctask类开始的所有这些行。 WeatherDBAccess是数据库类。该WeatherAzureAccess是蔚蓝类:
WeatherDBAccess._context = this.context;
WeatherDBAccess.Instance().AddWeatherEvent(wEvent);
//starts azure
WeatherAzureAccess.context = this.context;
WeatherAzureAccess.Instance();
//prep dailyinfo arraylist
dailyinfo = WeatherDBAccess.Instance().DailyWeatherEvents(dailyinfo);
,这是我的logcat,“从DB,当前温度:XX”的行会从方法打印为天蓝色:
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
我需要在第一个光标上使用FutureCallback来知道何时启动第二个光标?还是我需要使我的第一个游标全局,并等到第一个查询完成之前我重置一个游标做我的第二个查询?寻找一个解决方案,我已经知道,开始第二个光标是昂贵的。我的问题是很少使用第二个游标(可能只有onCreate()),并且第一个游标几乎总是会继续使用,因为它始终用于将内容发送到Azure。也FYI我关闭我的数据库onDestroy()。
首先,你的错误是:
java.lang.IllegalStateException:无法从 CursorWindow读取行1,列-1。确保光标在 从其访问数据之前正确初始化。
这意味着,你有结果(第1行),但你正在尝试读取无效列索引(col -1)。
问题区域很可能在这里:
wEvent.CurrTemp = dailycursor.getString(dailycursor.getColumnIndex(COLUMN_CURRENT_TEMPERATURES));
您从getColumnIndex
因为COLUMN_CURRENT_TEMPERATURES
在您的SQL查询不存在得到一个-1的结果。
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);
您需要包括你意图从你的SELECT语句读取的所有列:
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);
感谢您的答复!那么为什么我需要在android中使用'SELECT COLUMN_CURRENT_TEMPERATURES'和'SELECT avg(COLUMN_CURRENT_TEMPERATURES)'?我不认为我理解你的观点,因为温度列存在,它在查询中,它只是在avg()函数中使用。当我在我的sqlite数据库浏览器中运行这个查询时,它完美地工作。 –
这是因为当您使用avg()函数时,列的名称不再可用。您可以使用'avg(列)作为列名'给动态列一个名称。 – Knossos
好的,工作!会有更有效的方法来使用一个光标而不是两个?或者我有多好,因为第二个游标不会查询大量数据? –