Database Android：Cannot perform this operation because the connection pool has been closed

我在阅读StackOverflow关于这个问题的文章，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以下错误:

   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，使用此方法获取它的一个实例:

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(它在第cursor.moveToFirst()行崩溃，并出现了那个错误).它几乎从来不会坠毁，但有时会坠毁.

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 through all rows and adding to list
    Profile profile = new Profile();
    if (cursor.moveToFirst()) {
        doWhatEver();
    }
    cursor.close();
    db.close();

    return profile;
}

就这样，在我使用的所有方法中:

SQLiteDatabase db = this.getReadableDatabase(); (or Writable)

然后我关闭光标和数据库.在本例中，行中抛出错误:

cursor.moveToFirst();

如果我之前拨打this.getReadableDatabase()，我不明白为什么错误提示数据库已关闭.请支持！谢谢您:)