Android SQLite:尝试重新打开已经关闭的对象

Question

我正在尝试根据ISBN从我的库存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()"返回到此页面,然后尝试单击另一个listView对象时,才会出现该错误.我提出的String searchEntries[] = InventoryAdapter.getInventoryEntriesByISBN(searchQuery, isbn[position]);从onClickListener以前的for循环之前onClickListener和现在的作品.

如果我通过"finish()"从另一个活动返回此活动后尝试getInventoryEntriesByISBN,为什么它不起作用？

SearchResultsScreen发生错误:

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

并通过扩展,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

执行查询前检查数据库连接:

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

您也可以cursor.requery();再次使用相同的查询.

最后你还要关闭游标和数据库.

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

编辑:

我创建了DBHelper扩展的类SQLiteOpenHelper,这个类是类的内部类DatabaseHelper,该类有以下方法.

/** 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,请随时给我打电话.谢谢.

Answer 2

仅当我单击一个项目，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。

我移动了 String searchEntries[] = InventoryAdapter.getInventoryEntriesByISBN(searchQuery, isbn[position]); 从 onClickListener 到 onClickListener 之前的前一个 for 循环，现在它可以工作了。

正确的搜索结果屏幕如下：

搜索结果屏幕.java

// Set up search array
    final String Entries[][] = new String[isbn.length][9];
    for(int i = 0; i < isbn.length; i++)
    {
        searchArray.add(new InventoryItem(isbn[i], InventoryAdapter.getTitleAndAuthorByISBN(isbn[i])));
        Entries[i] = InventoryAdapter.getInventoryEntriesByISBN(searchQuery, 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[] = Entries[position];