安卓 SQLite : attempt to re-open an already-closed object

Question

我正在尝试根据 ISBN 从我的 Inventory 表中获取某些图书数据。但是，我收到一个错误:“尝试重新打开一个已经关闭的对象”。只有当我单击一个 listView 对象，转到另一个屏幕，通过“finish()”返回此页面，然后尝试单击另一个 listView 对象时，才会发生该错误。我将 String searchEntries[] = InventoryAdapter.getInventoryEntriesByISBN(searchQuery, isbn[position]); 从 onClickListener 移动到之前的 for 循环 onClickListener 现在它可以工作了。

如果我在通过“finish()”从另一个 Activity 返回此 Activity 后尝试 getInventoryEntriesByISBN，为什么它不起作用？

错误发生在 SearchResultsScreen:

String searchEntries[] = InventoryAdapter.getInventoryEntriesByISBN(searchQuery, isbn[position]);

并且通过扩展，发生在 InventoryAdapter:

Cursor cursor = db.rawQuery(query, new String[] {ISBN});

SearchResultsScreen.java

// Set up search array
    for(int i = 0; i < isbn.length; i++)
    {
        searchArray.add(new InventoryItem(isbn[i], InventoryAdapter.getTitleAndAuthorByISBN(isbn[i])));
    }
    Toast.makeText(getApplicationContext(), "searchArray.size()="+searchArray.size(), Toast.LENGTH_LONG).show();

    // add data in custom adapter
    adapter = new CustomAdapter(this, R.layout.list, searchArray);
    ListView dataList = (ListView) findViewById(R.id.list);
    dataList.setAdapter(adapter);

    // On Click ========================================================
    dataList.setOnItemClickListener(new OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position,
                long id) {
            String searchEntries[] = InventoryAdapter.getInventoryEntriesByISBN(searchQuery, isbn[position]);

InventoryAdapter.java(最相关的部分)

public String[] getInventoryEntriesByISBN(String search, String ISBN)
{
    String[] searchEntry = new String [9];
    //Query
    String query = "select * from INVENTORY where ISBN = ?";
    Cursor cursor = db.rawQuery(query, new String[] {ISBN});
    if(cursor.getCount()<1) // title Not Exist
    {
        cursor.close();
        for(int i = 0; i < 9; i++)
            searchEntry[i] = "Not Found";
        return searchEntry;
    }
    cursor.moveToFirst();

    //put data into respective variable
    int publish = cursor.getInt(cursor.getColumnIndex("PUBLISH_DATE"));
    String publishdate = ((Integer)publish).toString();
    String title = cursor.getString(cursor.getColumnIndex("TITLE"));
    String author = cursor.getString(cursor.getColumnIndex("AUTHOR"));
    String callNumber = cursor.getString(cursor.getColumnIndex("CALL_NUMBER"));
    int available = cursor.getInt(cursor.getColumnIndex("AVAILABLE_COUNT"));
    String availablecount = ((Integer)available).toString();
    int inventory = cursor.getInt(cursor.getColumnIndex("INVENTORY_COUNT"));
    String inventorycount = ((Integer)inventory).toString();
    int due = cursor.getInt(cursor.getColumnIndex("DUE_PERIOD"));
    String dueperiod = ((Integer)due).toString();
    int checkoutcount = cursor.getInt(cursor.getColumnIndex("COUNT"));
    String count = ((Integer)checkoutcount).toString();
    //combine variables into one array
    searchEntry[0] = ISBN;
    searchEntry[1] = title;
    searchEntry[2] = author;
    searchEntry[3] = publishdate;
    searchEntry[4] = callNumber;
    searchEntry[5] = availablecount;
    searchEntry[6] = inventorycount;
    searchEntry[7] = dueperiod;
    searchEntry[8] = count;

    cursor.close();
    return searchEntry;
}

public String getTitleAndAuthorByISBN(String ISBN)
    {
        int entriesFound = getNumSearchEntries(ISBN);
        if(entriesFound==0)
            entriesFound = 1;
        String searchEntry;
        //Query
        String query = "select * from INVENTORY where ISBN = ?";
        Cursor cursor = db.rawQuery(query, new String[] {ISBN});
        if(cursor.getCount()<1) // title Not Exist
        {
            cursor.close();
            searchEntry = "Not Found";
            return searchEntry;
        }
        cursor.moveToFirst();
        //put data into respective variable
        String title = cursor.getString(cursor.getColumnIndex("TITLE"));
        String author = cursor.getString(cursor.getColumnIndex("AUTHOR"));
        //combine variables into one String
        searchEntry = title + " / " + author;
        //close cursor and return
        cursor.close();
        return searchEntry;
    }

DataBaseHelper.java

public class DataBaseHelper extends SQLiteOpenHelper
{   
// Database Version
    private static final int DATABASE_VERSION = 1;

// Database Name
private static final String DATABASE_NAME = "database.db";

// ============================ End Variables ===========================

public DataBaseHelper(Context context, String name, CursorFactory factory, int version) 
{
           super(context, name, factory, version);
}

public DataBaseHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

// Called when no database exists in disk and the helper class needs
// to create a new one.
@Override
public void onCreate(SQLiteDatabase _db) 
{
        _db.execSQL(LoginDataBaseAdapter.USER_TABLE_CREATE);
        _db.execSQL(CheckOutDataBaseAdapter.CHECKOUT_TABLE_CREATE);
        _db.execSQL(InventoryAdapter.INVENTORY_TABLE_CREATE);
        _db.execSQL(StatisticsAdapter.STATISTICS_TABLE_CREATE);
}
// Called when there is a database version mismatch meaning that the version
// of the database on disk needs to be upgraded to the current version.
@Override
public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion) 
{
        // Log the version upgrade.
        Log.w("TaskDBAdapter", "Upgrading from version " +_oldVersion + " to " +_newVersion + ", which will destroy all old data");


        // Upgrade the existing database to conform to the new version. Multiple
        // previous versions can be handled by comparing _oldVersion and _newVersion
        // values.
        // on upgrade drop older tables
        _db.execSQL("DROP TABLE IF EXISTS " + LoginDataBaseAdapter.USER_TABLE_CREATE);
        _db.execSQL("DROP TABLE IF EXISTS " + CheckOutDataBaseAdapter.CHECKOUT_TABLE_CREATE);
        _db.execSQL("DROP TABLE IF EXISTS " + InventoryAdapter.INVENTORY_TABLE_CREATE);
        _db.execSQL("DROP TABLE IF EXISTS " + StatisticsAdapter.STATISTICS_TABLE_CREATE);

        // Create a new one.
        onCreate(_db);
}

}

Answer 1

在执行查询之前检查数据库连接:


if (!dbHelper.db.isOpen())
dbHelper.open();


你也可以使用cursor.requery();再次进行相同的查询。

最后您还必须关闭游标和数据库。

cursor.close();
db.close();

编辑:

我创建了 DBHelper扩展 SQLiteOpenHelper 的类, 这个类是 DatabaseHelper 的内部类类和那个类有以下方法。

/** For OPEN database **/
public synchronized DatabaseHelper open() throws SQLiteException {
    dbHelper = new DBHelper(context);
    db = dbHelper.getWritableDatabase();
    return this;
}

/** For CLOSE database **/
public void close() {
    dbHelper.close();
}

如果您仍有疑问，请随时联系我。谢谢。