我看了很多关于这个主题的话题，但没有人能回答我的问题。
我从并发线程访问我的数据库，我的SQLiteOpenHelper实现了单例设计模式，因此我只有一个应用程序实例。
我使用以下代码访问我的数据库：
SQLiteDatabase db = DatabaseHelper.getInstance().getWritableDatabase();
...
Do some update in the DB
...
db.close();
在elhadi的回答基础上，我遇到了类似的问题，即在多个异步任务中打开和关闭数据库连接。经过我的调查发现，不必要一直打开和关闭数据库连接。我最终采用的方法是对Application进行子类化，在onCreate期间执行单个数据库打开操作，onTerminate期间执行单个数据库关闭操作。然后设置一个静态getter来检索已经打开的SQLiteDatabase对象。虽然这种方式不太适合DI（依赖注入），但安卓目前还无法完全实现依赖注入。
实现方法如下：
public class MainApplication extends Application {
private static SQLiteDatabase database;
/**
* Called when the application is starting, before any other
* application objects have been created. Implementations
* should be as quick as possible...
*/
@Override
public void onCreate() {
super.onCreate();
try {
database = SQLiteDatabase.openDatabase("/data/data/<yourdbpath>", null, SQLiteDatabase.OPEN_READWRITE);
} catch (SQLiteException e) {
// Our app fires an event spawning the db creation task...
}
}
/**
* Called when the application is stopping. There are no more
* application objects running and the process will exit.
* <p>
* Note: never depend on this method being called; in many
* cases an unneeded application process will simply be killed
* by the kernel without executing any application code...
* <p>
*/
@Override
public void onTerminate() {
super.onTerminate();
if (database != null && database.isOpen()) {
database.close();
}
}
/**
* @return an open database.
*/
public static SQLiteDatabase getOpenDatabase() {
return database;
}
}
try {
database = SQLiteDatabase.openDatabase("/data/data/<yourdbpath>", null, SQLiteDatabase.OPEN_READWRITE);
} catch (SQLiteException e) {
// Create your database here!
database = SQLiteDatabase.openDatabase("/data/data/<your db path>", null, SQLiteDatabase.OPEN_READWRITE);
}
}
简略版
以上代码仅为一部分，实际上还需要注意第一次运行应用程序时的异常处理。我们的应用程序会触发一个事件来生成数据库。在应用程序中，我们注册了一个监听器（Android 的 BroadcastReceiver 框架），并且主应用程序活动的其中一项任务是检查 MainApplication 中的 database 静态变量是否为空。如果为空，则会产生一个异步任务来创建数据库，当它完成（即运行 onPostExecute() 方法）时，最终会触发事件，我们知道此事件将被我们在 try-catch 中注册的监听器捕获。该接收器作为 MainApplication 类的内部类存在，如下所示：
/**
* Listener waiting for the application to finish
* creating the database.
* <p>
* Once this has been completed the database is ready for I/O.
* </p>
*
* @author David C Branton
*/
public class OpenDatabaseReceiver extends BroadcastReceiver {
public static final String BROADCAST_DATABASE_READY = "oceanlife.core.MainApplication$OpenDatabaseReceiver.BROADCAST_DATABASE_READY";
/**
* @see android.content.BroadcastReceiver#onReceive(android.content.Context, android.content.Intent)
*/
@Override
public void onReceive(final Context context, final Intent intent) {
Log.i(CreatedDatabaseReceiver.class.getSimpleName(), String.format("Received filter event, '%s'", intent.getAction()));
database = SQLiteDatabase.openDatabase("/data/data/<your db path>", null, SQLiteDatabase.OPEN_READWRITE);
unregisterReceiver(openDatabaseReceiver);
// Broadcast event indicating that the creation process has completed.
final Intent databaseReady = new Intent();
databaseReady.setAction(BROADCAST_DATABASE_READY);
context.sendBroadcast(databaseReady);
}
}