问题
I have a databaseHandler. I need to count the rows in table. App crashes by this error: android attempt to reopen an already-closed object sqlitedatabase.
I simply use this code in activity:
db.getContactsCount();
But app crashes. Furthemore I want to reset the tables (delete table rows). I added the method below:
public void deleteTable() {
SQLiteDatabase db = this.getWritableDatabase();
db.delete("contacts", null, null);
}
It works good but I can't use this one:
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);
// Create tables again
onCreate(db);
}
This is the databasehandler:
public class DatabaseHandler extends SQLiteOpenHelper {
// All Static variables
// Database Version
private static final int DATABASE_VERSION = 1;
// Database Name
private static final String DATABASE_NAME = "contactsManager";
// Contacts table name
private static final String TABLE_CONTACTS = "contacts";
// Contacts Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_PH_NO = "phone_number";
public DatabaseHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
+ KEY_PH_NO + " TEXT" + ")";
db.execSQL(CREATE_CONTACTS_TABLE);
}
// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Drop older table if existed
db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);
// Create tables again
onCreate(db);
}
/**
* All CRUD(Create, Read, Update, Delete) Operations
*/
// Adding new contact
void addContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, contact.getName()); // Contact Name
values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone
// Inserting Row
db.insert(TABLE_CONTACTS, null, values);
db.close(); // Closing database connection
}
// Getting single contact
Contact getContact(int id) {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
KEY_NAME, KEY_PH_NO }, KEY_ID + "=?",
new String[] { String.valueOf(id) }, null, null, null, null);
if (cursor != null)
cursor.moveToFirst();
Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
cursor.getString(1), cursor.getString(2));
// return contact
return contact;
}
// Getting All Contacts
public List<Contact> getAllContacts() {
List<Contact> contactList = new ArrayList<Contact>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_CONTACTS;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Contact contact = new Contact();
contact.setID(Integer.parseInt(cursor.getString(0)));
contact.setName(cursor.getString(1));
contact.setPhoneNumber(cursor.getString(2));
// Adding contact to list
contactList.add(contact);
} while (cursor.moveToNext());
}
// return contact list
return contactList;
}
// Updating single contact
public int updateContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_NAME, contact.getName());
values.put(KEY_PH_NO, contact.getPhoneNumber());
// updating row
return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
new String[] { String.valueOf(contact.getID()) });
}
// Deleting single contact
public void deleteContact(Contact contact) {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_CONTACTS, KEY_ID + " = ?",
new String[] { String.valueOf(contact.getID()) });
db.close();
}
// Getting contacts Count
public int getContactsCount() {
String countQuery = "SELECT * FROM " + TABLE_CONTACTS;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(countQuery, null);
cursor.close();
// return count
return cursor.getCount();
}
public void Upgrade (SQLiteDatabase db, int oldVersion, int newVersion) {
String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
+ KEY_PH_NO + " TEXT" + ")";
db.execSQL(CREATE_CONTACTS_TABLE);
}
// Deleting single contact
public void deleteTable() {
SQLiteDatabase db = this.getWritableDatabase();
db.delete("contacts", null, null);
}
}
回答1:
It happens because of the:
db.close();
in the methods:
void addContact(Contact contact)
public void deleteContact(Contact contact)
You should not close the connection to the underlying database unless you really do not intend to work with it anymore.
Use SQLiteOpenHelper:close, when you've finished your work.
Moreover, calls to getReadableDatabase() and getWriteableDatabase() return the same database object 99% of a time, and they do not reinitialize database connection closed manually by you.
Don't get fooled by these method names.
回答2:
I would like to suggest you that, dont close database object before complete your database work.
SQLiteDatabase db;
db = this.getWritableDatabase();
or
db = this.getReadableDatabase();
Above both method give us database object using helper class and using this object we can do different actions on database. But in your scenario, I think so you closed database object before complete database operation. So closed after done all operation by using
db.close();
回答3:
The onUpgrade is when you made changes to your database (ie adding tables) so there is now a new version of your database. Your:
private static final int DATABASE_VERSION = 1;
is now
private static final int DATABASE_VERSION = 2;
Because the database version is now higher newer version the OnUpgrade() method is called and updates the database.
回答4:
it basically happens because of cursor.close(); since you are closing the cursor object before you are returning its count.
回答5:
I should have defined int count = cursor.getCount(); before closing the database. It seems return cursor.getCount(); after closing the database is a useless effort.
At last removing db.close(); at the end of delete and remove methods was necessary.
Adding this code instead in handler instead helped alot:
public void closeDB() {
SQLiteDatabase db = this.getReadableDatabase();
if (db != null && db.isOpen())
db.close();
}
Manipulating close function inside activity at the end of database usage was better. Thanks to @Drew.
I still can't understand the usage of onUpgrade inside handler ???
来源：https://stackoverflow.com/questions/23166323/attempt-to-reopen-an-already-closed-object-sqlitedatabase