sqlitedatase在重新创建活动时出现错误

在意图被重新创建后，我得到每个数据库查询异常。我认为这可能是因为重新创造活动的方式，但我不知道如何解决这个问题。

我在改变语言和暗模式后重新创建它。

当重新创建活动时抛出异常:

试图重新打开已关闭的对象:sqliteddatabase:

活动

private lateinit var db: SQLiteDatabase
private lateinit var oh: LOTDatabaseHelper
...

onCreate

...
oh = LOTDatabaseHelper(this)
db = oh.readableDatabase
...

onDestroy

...
db.close()
oh.close()
...

和如何创建intent

val intent = intent
intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION)
startActivity(intent)
finish()

编辑:

我发现Activity被创建了大约两次，然后一个被留下，其余的被销毁。OnDestroy似乎对所有活动都有效，并关闭了数据库，这是不可能的。

现在我正在导航到启动屏幕，然后到使用数据库的活动，一切都在工作。那么，当Activity被自己取代时，为什么生命周期不能很好地工作呢?

打开已经关闭的数据库通常是由于打开和关闭不匹配引起的。

通常解决方法是不打开和关闭数据库(除非特别需要，例如从备份副本恢复数据库，或者强制WAL检查点备份数据库)，而是只打开数据库一次。

通常不需要打开和关闭数据库，因为当应用程序完成时，数据库将被关闭(你可以总是关闭它，如果最上面的活动的onDestroy)。此外，打开数据库是一种资源消耗，所以太多的打开是资源浪费/效率低下。

可能参见Android SQLite DB何时关闭

我建议去掉所有的close。您可能还希望考虑单例方法，甚至可能在Helper中拥有所有DB功能。

作为一个例子，可以考虑:-

HelperDBHelper: -

class LOTDatabaseHelper(context: Context): SQLiteOpenHelper(
context,
DATABASE_NAME,
null,
DATABASE_VERSION) {
companion object {
const val DATABASE_NAME = "my.db"
const val DATABASE_VERSION = 1
@Volatile
private var instance: SQLiteDatabase? = null
fun getInstance(context: Context): SQLiteDatabase {
if (instance == null) {
instance = LOTDatabaseHelper(context).writableDatabase
}
return instance as SQLiteDatabase
}
}
override fun onCreate(db: SQLiteDatabase?) {
db?.execSQL(Table1.CREATE_SQL)
}
override fun onUpgrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
TODO("Not yet implemented")
}
override fun onDowngrade(db: SQLiteDatabase?, oldVersion: Int, newVersion: Int) {
super.onDowngrade(db, oldVersion, newVersion)
}
fun insert(name: String): Long {
val cv = ContentValues()
cv.put(Table1.COL_NAME,name)
return instance!!.insert(Table1.TABLE_NAME,null,cv)
}
fun getAllFromTable1() : Cursor {
return instance!!.query(Table1.TABLE_NAME,null,null,null,null,null,"${Table1.COL_NAME} ASC")
}
@SuppressLint("Range")
fun logAll() {
val csr = getAllFromTable1()
var row = 1
val nameix = csr.getColumnIndex(COL_NAME)
while (csr.moveToNext()) {
Log.d("CURSORINFO","Row ${row++} ${COL_NAME} is ${csr.getString(csr.getColumnIndex(
COL_NAME))}")
//val test = csr.getString(csr.getColumnIndex("${COL_NAME}"))
}
csr.close()
}
// Table stuff
class Table1 {
companion object {
const val TABLE_NAME = "table1"
const val COL_ID = BaseColumns._ID
const val COL_NAME = "${TABLE_NAME}_name"
const val CREATE_SQL = "CREATE TABLE IF NOT EXISTS $TABLE_NAME (${COL_ID} INTEGER PRIMARY KEY, $COL_NAME TEXT);"
}
}
}

调用第二个活动的初始活动MainActivity: -

class MainActivity : AppCompatActivity() {
val TAG = "MAINACTIVITYINFO"
private lateinit var dbother: DBHelper
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
dbother = DBHelper.getInstance(this)!!
dbother.insert("TESTOTHER") // Use the Insert in the DBHelper
/* of course you can still get an SQLiteDatabase */
/* There is very little use getting readable as it gets writable */
/* so get writable is more accurate description */
var sqliteDatabase = dbother.writableDatabase //<<<<<< can be used
logCursorInfo(dbother.allAsCursor)
// NOW Start the other Activity
Log.d(TAG,"starting Activity2")
intent = Intent(this,Activity2::class.java)
startActivity(intent)
Log.d(TAG,"after starting Activity2")
}
override fun onDestroy() {
super.onDestroy()
Log.d("ONDESTROY","On Destroy invoked.")
}
override fun onResume() {
super.onResume()
Log.d(TAG,"On Resume invoked")
dbother = DBHelper.getInstance(this)!!
}
//
@SuppressLint("Range")
fun logCursorInfo(csr: Cursor) {
val nameix = csr.getColumnIndex(LOTDatabaseHelper.Table1.COL_NAME)
val idix = csr.getColumnIndex(LOTDatabaseHelper.Table1.COL_ID)
while (csr.moveToNext()) {
//Log.d(TAG,"${LOTDatabaseHelper.Table1.COL_ID} = ${csr.getString(idix)} ${LOTDatabaseHelper.Table1.COL_NAME} = ${csr.getString(nameix)}")
Log.d(TAG,"${csr.getString(csr.getColumnIndex(LOTDatabaseHelper.Table1.COL_NAME))}")
}
}
companion object {
var counter: Int = 0
}
}

这使用DBHelper，但获得一个实例，然后添加几行，提取它们，然后启动第二个活动。

Activity2出现问题的活动:-

class Activity2 : AppCompatActivity() {
val TAG = "ACTIVITY2INFO"
private lateinit var dbother: DBHelper
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_2)
Log.d(TAG,"Activity 2 Started (onCreate). $this")
dbother = DBHelper.getInstance(this)!! // Get the Database
dbother.insert("TESTOTHER_ACTIVITY2") // Add a row
var csr = dbother.allAsCursor // get All the rows
DatabaseUtils.dumpCursor(csr) // dump the cursor
csr.close() // close the cursor
/* Start another activity (will loop so stop with counter)*/
Log.d(TAG,"Restarting Activity. counter is ${counter++} $this")
if (counter < 3) {
val intent = intent
intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION)
startActivity(intent) //<<<<<<<<<< RUN 1 Not the Way as starts a new activity
/* Perhaps the following???? */
// this.intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION)
//this.recreate() //<<<<<<<<<< RUN 2 perhaps the way but no intent
}
Log.d(TAG,"Finishing Activity 2 $this")
finish()
}
companion object {
var counter: Int = 0
}
override fun onResume() {
super.onResume()
Log.d(TAG,"OnResume Invoked. $this")
}
override fun onDestroy() {
super.onDestroy()
Log.d(TAG,"OnDestory (after super call - before db close and helper close. $this)")
Log.d(TAG,"OnDestory (after all. $this)")
}
}

这将获得一个DBHelper实例，插入一行，提取所有数据，然后启动另一个活动，注意这将无休止地循环，因此计数。

希望这些评论会有所帮助。

可以看到，我包含了相当多的日志记录。然而，正如建议的那样，数据库永远不会关闭。

运行应用程序

这是运行应用程序的结果，即日志(来自新安装):-

2021-10-06 19:52:50.715  D/DBHELPERINFO: getInstance returning instance a.a.so69454766kotlinsqlite.DBHelper@59860ab
2021-10-06 19:52:50.717  D/MAINACTIVITYINFO: TESTOTHER
2021-10-06 19:52:50.717  D/MAINACTIVITYINFO: starting Activity2
2021-10-06 19:52:50.724  D/MAINACTIVITYINFO: after starting Activity2
2021-10-06 19:52:50.734  D/MAINACTIVITYINFO: On Resume invoked
2021-10-06 19:52:50.734  D/DBHELPERINFO: getInstance returning instance a.a.so69454766kotlinsqlite.DBHelper@59860ab
2021-10-06 19:52:50.848  D/ACTIVITY2INFO: Activity 2 Started (onCreate). a.a.so69454766kotlinsqlite.Activity2@3269902
2021-10-06 19:52:50.848  D/DBHELPERINFO: getInstance returning instance a.a.so69454766kotlinsqlite.DBHelper@59860ab
2021-10-06 19:52:50.850  I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@950aa67
2021-10-06 19:52:50.851  I/System.out: 0 {
2021-10-06 19:52:50.852  I/System.out:    _id=1
2021-10-06 19:52:50.852  I/System.out:    table1_name=TESTOTHER
2021-10-06 19:52:50.852  I/System.out: }
2021-10-06 19:52:50.852  I/System.out: 1 {
2021-10-06 19:52:50.852  I/System.out:    _id=2
2021-10-06 19:52:50.852  I/System.out:    table1_name=TESTOTHER_ACTIVITY2
2021-10-06 19:52:50.852  I/System.out: }
2021-10-06 19:52:50.852  I/System.out: <<<<<
2021-10-06 19:52:50.856  D/ACTIVITY2INFO: Restarting Activity. counter is 0 a.a.so69454766kotlinsqlite.Activity2@3269902
2021-10-06 19:52:50.864  D/ACTIVITY2INFO: Finishing Activity 2 a.a.so69454766kotlinsqlite.Activity2@3269902
2021-10-06 19:52:51.020  D/ACTIVITY2INFO: Activity 2 Started (onCreate). a.a.so69454766kotlinsqlite.Activity2@7db7a75
2021-10-06 19:52:51.020  D/DBHELPERINFO: getInstance returning instance a.a.so69454766kotlinsqlite.DBHelper@59860ab
2021-10-06 19:52:51.021  I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@7fc80ae
2021-10-06 19:52:51.021  I/System.out: 0 {
2021-10-06 19:52:51.021  I/System.out:    _id=1
2021-10-06 19:52:51.021  I/System.out:    table1_name=TESTOTHER
2021-10-06 19:52:51.021  I/System.out: }
2021-10-06 19:52:51.021  I/System.out: 1 {
2021-10-06 19:52:51.021  I/System.out:    _id=2
2021-10-06 19:52:51.022  I/System.out:    table1_name=TESTOTHER_ACTIVITY2
2021-10-06 19:52:51.022  I/System.out: }
2021-10-06 19:52:51.022  I/System.out: 2 {
2021-10-06 19:52:51.022  I/System.out:    _id=3
2021-10-06 19:52:51.022  I/System.out:    table1_name=TESTOTHER_ACTIVITY2
2021-10-06 19:52:51.022  I/System.out: }
2021-10-06 19:52:51.022  I/System.out: <<<<<
2021-10-06 19:52:51.023  D/ACTIVITY2INFO: Restarting Activity. counter is 1 a.a.so69454766kotlinsqlite.Activity2@7db7a75
2021-10-06 19:52:51.030  D/ACTIVITY2INFO: Finishing Activity 2 a.a.so69454766kotlinsqlite.Activity2@7db7a75
2021-10-06 19:52:51.081  D/ACTIVITY2INFO: Activity 2 Started (onCreate). a.a.so69454766kotlinsqlite.Activity2@3433874
2021-10-06 19:52:51.081  D/DBHELPERINFO: getInstance returning instance a.a.so69454766kotlinsqlite.DBHelper@59860ab
2021-10-06 19:52:51.082  I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@5c713d1
2021-10-06 19:52:51.082  I/System.out: 0 {
2021-10-06 19:52:51.082  I/System.out:    _id=1
2021-10-06 19:52:51.082  I/System.out:    table1_name=TESTOTHER
2021-10-06 19:52:51.082  I/System.out: }
2021-10-06 19:52:51.082  I/System.out: 1 {
2021-10-06 19:52:51.083  I/System.out:    _id=2
2021-10-06 19:52:51.083  I/System.out:    table1_name=TESTOTHER_ACTIVITY2
2021-10-06 19:52:51.083  I/System.out: }
2021-10-06 19:52:51.083  I/System.out: 2 {
2021-10-06 19:52:51.083  I/System.out:    _id=3
2021-10-06 19:52:51.083  I/System.out:    table1_name=TESTOTHER_ACTIVITY2
2021-10-06 19:52:51.083  I/System.out: }
2021-10-06 19:52:51.083  I/System.out: 3 {
2021-10-06 19:52:51.083  I/System.out:    _id=4
2021-10-06 19:52:51.083  I/System.out:    table1_name=TESTOTHER_ACTIVITY2
2021-10-06 19:52:51.083  I/System.out: }
2021-10-06 19:52:51.083  I/System.out: <<<<<
2021-10-06 19:52:51.084  D/ACTIVITY2INFO: Restarting Activity. counter is 2 a.a.so69454766kotlinsqlite.Activity2@3433874
2021-10-06 19:52:51.084  D/ACTIVITY2INFO: Finishing Activity 2 a.a.so69454766kotlinsqlite.Activity2@3433874
2021-10-06 19:52:51.097  D/MAINACTIVITYINFO: On Resume invoked
2021-10-06 19:52:51.097  D/DBHELPERINFO: getInstance returning instance a.a.so69454766kotlinsqlite.DBHelper@59860ab

需要注意的一点是，检索到的DBHelper实例总是DBHelper@59860ab(即单个实例)。

正如你所注意到的，活动发生了什么，另一个是被启动。您可以尝试使用注释掉的:-

/* Perhaps the following???? */
// this.intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION)
//this.recreate() //<<<<<<<<<< RUN 2 perhaps the way but no intent

我不确定这是否会达到你想要的。

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