问题描述
我已经在我的应用程序中合并了数据库备份和还原。 所有这些都工作正常，但是当我还原数据库时，由于使用单例DBHelper并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。
关闭该应用程序并重新启动，将使用新数据库。 但是，不要告诉用户这样做。 我想无缝访问恢复的数据库。
这是检测并成功还原后报告的代码：
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）
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);
}
.......
认为您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：-
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：-
java.lang.IllegalStateException：尝试重新打开一个已经关闭的对象：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)
1楼
诀窍很简单，不要关闭数据库，只需重置DBHelper 。
因此，重新打开方法可能是：
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。
因此，检测并报告还原成功的代码可能是：-
if(copytaken && origdeleted && restoredone) {
errlist.add("Database successfully restored.");
resulttitle = "Restore was successful.";
DBHelper.reopen(context); <== implemented as below
}
2楼
对我有用的重新打开代码是：
public void reopen(Context context, String DbFilePath) {
instance = new DBHelper(context, DbFilePath);
}
与上一个答案的区别是从函数定义中删除了“静态”，这也要求实例也为静态。 这阻止了实际重新打开数据库