使用单例作为数据库助手时，如何在还原后刷新/重新打开SQLite数据库 [英] How can I refresh/reopen an SQLite database after restoring it, when using a singleton for the database helper
问题描述
我已在我的应用程序中合并了数据库备份和还原.一切正常，除了在还原数据库时，由于使用单例DBHelper且仅在应用程序关闭时关闭数据库，因此还原后继续使用数据库的内存副本.
I have incorporated Database Backup and restore in my App. This all works fine except that when I restore the database, due to the use of a singleton DBHelper along with only closing the database when the App closes, the in-memory copy of the Database continues to be used after the restore.
关闭应用程序并重新启动，将使用新数据库.但是，而不是告诉用户执行此操作.我想无缝访问恢复的数据库.
Closing the App and re-starting uses the new database. However, rather than tell the user to do this. I would like to seamlessly access the restored database.
这是检测并成功还原后报告的代码:-
This is the code that detects and then reports upon a successful restore :-
if(copytaken && origdeleted && restoredone) {
errlist.add("Database successfully restored." +
"\n\nYou should close the ShopWise App and then restart it.");
resulttitle = "Restore was successful.";
//DBHelper.reopen(context); <== implemented as below
}
..... Displays dialog with text from above
这是DBHelper(注意，expand方法用于创建/修改表)
This is the DBHelper (note expand method is used to create/amend the tables)
class DBHelper extends SQLiteOpenHelper {
private static final String DBNAME = DBConstants.DATABASE_NAME;
/**
* Consrtuctor
*
* @param context activity context
* @param name database name
* @param factory cursorfactory
* @param version database version
*/
DBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}
/**
* Instantiates a new Db helper.
*
* @param context the context
*/
DBHelper(Context context) {
super(context, DBConstants.DATABASE_NAME, null, 1);
}
private static DBHelper instance;
/**
* Gets helper.
*
* @param context the context
* @return the helper
*/
static synchronized DBHelper getHelper(Context context) {
if(instance == null) {
instance = new DBHelper(context);
}
return instance;
}
@Override
public void onCreate(SQLiteDatabase db) {
expand(db, false);
}
.......
认为应该关闭数据库然后重新打开它.我尝试在DBHelper中添加重新打开方法，如下所示:-
Thinking that you should close the database an reopen it. I tried adding a reopen method in the DBHelper as follows:-
public static void reopen(Context context) {
instance.close();
instance = null;
instance = new DBHelper(context);
}
，然后在恢复正常时(根据注释)从代码中调用此方法.但是，这导致以下结果:-
and then invoked this from within the code when the restore was OK (as per comment). However, this results in the following :-
java.lang.IllegalStateException:尝试重新打开一个已经关闭的 对象:SQLiteDatabase:
java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase:
02-16 16:41:20.938 2683-3050/mjt.shopwise E/SQLiteLog: (28) file unlinked while open: /data/data/mjt.shopwise/databases/ShopWise
02-16 16:41:25.171 2683-2683/mjt.shopwise D/AndroidRuntime: Shutting down VM
02-16 16:41:25.171 2683-2683/mjt.shopwise E/AndroidRuntime: FATAL EXCEPTION: main
Process: mjt.shopwise, PID: 2683
java.lang.RuntimeException: Unable to resume activity {mjt.shopwise/mjt.shopwise.MainActivity}: java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase: /data/data/mjt.shopwise/databases/ShopWise
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2986)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3017)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1347)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase: /data/data/mjt.shopwise/databases/ShopWise
at android.database.sqlite.SQLiteClosable.acquireReference(SQLiteClosable.java:55)
at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1312)
at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1255)
at mjt.shopwise.DBCommonMethods.getTableRows(DBCommonMethods.java:106)
at mjt.shopwise.DBCommonMethods.getTableRows(DBCommonMethods.java:59)
at mjt.shopwise.DBCommonMethods.getTableRowCount(DBCommonMethods.java:29)
at mjt.shopwise.DBCommonMethods.getTableRowCount(DBCommonMethods.java:43)
at mjt.shopwise.DBShopMethods.getShopCount(DBShopMethods.java:44)
at mjt.shopwise.MainActivity.getDBCounts(MainActivity.java:207)
at mjt.shopwise.MainActivity.onResume(MainActivity.java:163)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1257)
at android.app.Activity.performResume(Activity.java:6076)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2975)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3017)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1347)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
推荐答案
诀窍很简单，只要重置DBHelper，就不要关闭数据库.
The trick is very simple, do not close the database just reset the DBHelper.
所以重新打开方法可能是:-
So the reopen method could be:-
public static void reopen(Context context) {
instance = new DBHelper(context);
}
当然，您也可以删除告诉用户关闭并重新启动应用程序的文本.
Of course, you could also do away with the text telling the user to close and restart the App.
因此，检测并报告成功还原的代码可能是:-
So the code that detects and reports on a successful restore could be:-
if(copytaken && origdeleted && restoredone) {
errlist.add("Database successfully restored.");
resulttitle = "Restore was successful.";
DBHelper.reopen(context); <== implemented as below
}
这篇关于使用单例作为数据库助手时，如何在还原后刷新/重新打开SQLite数据库的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
