尝试重新打开一个已经关闭的对象 sqlitedatabase [英] Attempt to reopen an already-closed object sqlitedatabase
问题描述
我有一个databaseHandler.我需要计算表中的行数.应用程序因以下错误而崩溃:android 尝试重新打开已关闭的对象 sqlitedatabase
.
我只是在活动中使用此代码:
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();
但是应用程序崩溃了.此外,我想重置表格(删除表格行).我添加了以下方法:
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);
}
效果很好,但我不能用这个:
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);
}
这是数据库处理程序:
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);
}
}
推荐答案
发生的原因:
db.close();
在方法中:
void addContact(Contact contact)
public void deleteContact(Contact contact)
您不应该关闭与底层数据库的连接,除非您真的不打算再使用它.完成工作后,使用 SQLiteOpenHelper:close
.
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.
此外,对 getReadableDatabase()
和 getWriteableDatabase()
的调用在 99% 的情况下返回相同的数据库对象,而它们不会重新初始化您手动关闭的数据库连接.
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.
不要被这些方法名称所迷惑.
Don't get fooled by these method names.
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