如何安全地关闭光标和数据库？

Question

我使用Cursor从数据库中获取记录.这是完美的工作.但是,当我使用这段代码时,我在Logcat中遇到了一些错误

public Cursor fetchAll()
{
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.query(t1, new String[] {"_id",name, date, prior, time, dateformat}, null, null, null, null, prior); 
    return cursor;
}

我的logcat是 -

12-16 14:49:20.774: E/Database(18611): close() was never explicitly called on database '/data/data/com.android.application/databases/appZ.db' 
12-16 14:49:20.774: E/Database(18611): android.database.sqlite.DatabaseObjectNotClosedException: Application did not close the cursor or database object that was opened here
12-16 14:49:20.774: E/Database(18611):  at android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1810)
12-16 14:49:20.774: E/Database(18611):  at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:817)
12-16 14:49:20.774: E/Database(18611):  at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:851)
12-16 14:49:20.774: E/Database(18611):  at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:844)
12-16 14:49:20.774: E/Database(18611):  at android.app.ContextImpl.openOrCreateDatabase(ContextImpl.java:540)
12-16 14:49:20.774: E/Database(18611):  at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
12-16 14:49:20.774: E/Database(18611):  at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
12-16 14:49:20.774: E/Database(18611):  at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:158)
12-16 14:49:20.774: E/Database(18611):  at com.android.todoapplication.DBHelper.fetchAll(DBHelper.java:91)
12-16 14:49:20.774: E/Database(18611):  at com.android.todoapplication.ApplicationActivity.sc_adapter(ApplicationActivity.java:1210)
12-16 14:49:20.774: E/Database(18611):  at com.android.todoapplication.ApplicationActivity.refresh_data(ApplicationActivity.java:1195)
12-16 14:49:20.774: E/Database(18611):  at com.android.todoapplication.ApplicationActivity.onKeyDown(ApplicationActivity.java:1440)
12-16 14:49:20.774: E/Database(18611):  at android.view.KeyEvent.dispatch(KeyEvent.java:1037)
12-16 14:49:20.774: E/Database(18611):  at android.app.Activity.dispatchKeyEvent(Activity.java:2068)
12-16 14:49:20.774: E/Database(18611):  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1643)
12-16 14:49:20.774: E/Database(18611):  at android.view.ViewRoot.deliverKeyEventToViewHierarchy(ViewRoot.java:2471)
12-16 14:49:20.774: E/Database(18611):  at android.view.ViewRoot.handleFinishedEvent(ViewRoot.java:2441)
12-16 14:49:20.774: E/Database(18611):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1735)
12-16 14:49:20.774: E/Database(18611):  at android.os.Handler.dispatchMessage(Handler.java:99)
12-16 14:49:20.774: E/Database(18611):  at android.os.Looper.loop(Looper.java:123)
12-16 14:49:20.774: E/Database(18611):  at android.app.ActivityThread.main(ActivityThread.java:4627)
12-16 14:49:20.774: E/Database(18611):  at java.lang.reflect.Method.invokeNative(Native Method)
12-16 14:49:20.774: E/Database(18611):  at java.lang.reflect.Method.invoke(Method.java:521)
12-16 14:49:20.774: E/Database(18611):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
12-16 14:49:20.774: E/Database(18611):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
12-16 14:49:20.774: E/Database(18611):  at dalvik.system.NativeStart.main(Native Method)

我从这里提到了一些东西.他们告诉使用getReadableDatabase().我也在使用那种方法.而且,我也使用这种方法,

public Cursor fetchAll()
{
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.query(t1, new String[] {"_id",name, date, prior, time, dateformat}, null, null, null, null, prior); 
   if (cursor!=null)
    {
        cursor.close();
    }
   if (db!=null)
    {
        db.close();
    }
    return cursor;
}

之后有错误像 -

Database wasn't open.

之后,我的数据库中也出现了这个错误.所以任何人都告诉我如何在获取记录后获取光标和数据库的安全关闭.

Answer 1

编辑:如果您返回已经关闭的光标,则无法使用它.在调用方法之前打开数据库,然后在调用方法后关闭游标然后关闭数据库.

完成后可以关闭光标,如下所示:

Cursor cursor = fetchAll();
... // Do your work with the cursor
cursor.close();

或者,如果您正在使用活动中的光标,并且需要重新查询(当活动重新启动,停止...时),您可以使用:

Cursor cursor = fetchAll();
startManagingCursor(cursor); // Android will take care of the cursor for you
// Do your work with the cursor

要关闭数据库(在关闭游标之后,或者如果在一个活动中onDestroy()最好):

dbhelper.close();