相关疑难解决方法(0)

在Android应用程序中对SQLite数据库执行查询时,最佳做法是什么？

从AsyncTask的doInBackground运行插入,删除和选择查询是否安全？或者我应该使用UI线程？我认为数据库查询可能"很重",不应该使用UI线程,因为它可以锁定应用程序 - 导致应用程序无响应(ANR).

如果我有几个AsyncTasks,他们应该共享一个连接还是应该分别打开一个连接？

这些方案是否有最佳实践？

我正在阅读有关此问题的stackoverflow,但我仍然没有找到解决方案.我注意到有时,我的应用程序会抛出此错误:

   java.lang.IllegalStateException: Cannot perform this operation because the connection pool has been closed.
        at android.database.sqlite.SQLiteConnectionPool.throwIfClosedLocked(SQLiteConnectionPool.java:962)
        at android.database.sqlite.SQLiteConnectionPool.waitForConnection(SQLiteConnectionPool.java:599)
        at android.database.sqlite.SQLiteConnectionPool.acquireConnection(SQLiteConnectionPool.java:348)
        at android.database.sqlite.SQLiteSession.acquireConnection(SQLiteSession.java:894)
        ...

我有一个名为DatabaseHelper.java的文件,使用这种方法获取它的实例:

public static DatabaseHelper getInstance(Context context) {
    if (mInstance == null) {
        mInstance = new DatabaseHelper(context.getApplicationContext());
    }
    return mInstance;
}

然后我有像这样的方法(它在行cursor.moveToFirst()中崩溃与该错误).它几乎从不崩溃,但有时它会崩溃.

public Profile getProfile(long id) {
    SQLiteDatabase db = this.getReadableDatabase();

    String selectQuery = "SELECT * FROM " + TABLE_PROFILES + " WHERE " + KEY_PROFILES_ID + " = " + id;
    Cursor cursor = db.rawQuery(selectQuery, null);

    // looping …

我们AsyncTasks用来访问数据库表和游标.

不幸的是,我们偶尔会看到有关数据库被锁定的例外情况.

E/SQLiteOpenHelper(15963): Couldn't open iviewnews.db for writing (will try read-only):
E/SQLiteOpenHelper(15963): android.database.sqlite.SQLiteException: database is locked
E/SQLiteOpenHelper(15963):  at     android.database.sqlite.SQLiteDatabase.native_setLocale(Native Method)
E/SQLiteOpenHelper(15963):  at     android.database.sqlite.SQLiteDatabase.setLocale(SQLiteDatabase.java:1637)
E/SQLiteOpenHelper(15963):  at     android.database.sqlite.SQLiteDatabase.<init>(SQLiteDatabase.java:1587)
E/SQLiteOpenHelper(15963):  at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:638)
E/SQLiteOpenHelper(15963):  at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:659)
E/SQLiteOpenHelper(15963):  at android.database.sqlite.SQLiteDatabase.openOrCreateDatabase(SQLiteDatabase.java:652)
E/SQLiteOpenHelper(15963):  at android.app.ApplicationContext.openOrCreateDatabase(ApplicationContext.java:482)
E/SQLiteOpenHelper(15963):  at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193)
E/SQLiteOpenHelper(15963):  at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
E/SQLiteOpenHelper(15963):  at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:158)
E/SQLiteOpenHelper(15963):  at com.iview.android.widget.IViewNewsTopStoryWidget.initData(IViewNewsTopStoryWidget.java:73)
E/SQLiteOpenHelper(15963):  at com.iview.android.widget.IViewNewsTopStoryWidget.updateNewsWidgets(IViewNewsTopStoryWidget.java:121)
E/SQLiteOpenHelper(15963):  at com.iview.android.async.GetNewsTask.doInBackground(GetNewsTask.java:338)
E/SQLiteOpenHelper(15963):  at com.iview.android.async.GetNewsTask.doInBackground(GetNewsTask.java:1)
E/SQLiteOpenHelper(15963):  at android.os.AsyncTask$2.call(AsyncTask.java:185)
E/SQLiteOpenHelper(15963):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:256)
E/SQLiteOpenHelper(15963):  at java.util.concurrent.FutureTask.run(FutureTask.java:122)
E/SQLiteOpenHelper(15963):  at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:648)
E/SQLiteOpenHelper(15963):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:673)
E/SQLiteOpenHelper(15963):  at java.lang.Thread.run(Thread.java:1060)

有没有人有一个代码的一般例子,它从一个读取的不同线程写入数据库,我们如何确保线程安全. …

我使用此类来管理与底层SQLiteDatabase的连接

public class BasicDataSource {

    protected DatabaseHandler dbHelper;
    protected volatile SQLiteDatabase readable_database;
    protected volatile SQLiteDatabase writable_database;
    protected Object read_lock = new Object();
    protected Object write_lock = new Object();
    protected Context context;

    protected BasicDataSource(Context ctx) {
        dbHelper = DatabaseHandler.getInstance(ctx);
        getReadableDatabase();
        dbHelper.onCreate(getWritableDatabase());
        this.context = ctx;
    }

    public synchronized void close() {
        dbHelper.close();
    }

    protected void closeInsertHelpers(InsertHelper... helpers) {
        for (InsertHelper ih : helpers) {
            if (ih != null)
                ih.close();
        }
    }

    protected SQLiteDatabase getReadableDatabase() {
        synchronized (read_lock) {
            if (readable_database == null …