Come eliminare tabelle e database utilizzando Sqiltehelper in Android

Question

Ho creato una chiamata di classe DatabaseHandler che estende SQLiteOpenHelper. Voglio esplicare cancellato il database o la tabella sul clic del pulsante. Quali sono i parametri che devo passare al metodo di chiamata? Ecco il codice di riferimento:

public class DatabaseHandler extends SQLiteOpenHelper 
{ 

// All Static variables 
// Database Version 
public static final int DATABASE_VERSION =1; 

// Database Name 
public static final String DATABASE_NAME = "EmployeeDB"; 

// Contacts table name 
public 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); 
} 


@Override 
public void onCreate(SQLiteDatabase db) 
{ 
    // TODO Auto-generated method stub 

    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); 

} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
{ 
    // TODO Auto-generated method stub 
    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(id, 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 DeleteDatabase(SQLiteDatabase db,String table) 
{ 


    db.execSQL("DELETE FROM " + table); 
    db.close(); 
} 

} 

Answer 1

Difficile rispondere senza più contesto, ma la query SQLite finale sarebbe:

db.execSQL("DROP TABLE IF EXISTS tablename"); 

Dove db è un riferimento a un oggetto SQLiteDatabase.

e cancellare dati

context.deleteDatabase(DATABASE_NAME); 

Answer 2

Il codice qui sotto cancella le tabelle da DB:

db.execSQL("delete from " + DBNAME); 

Per eliminare database:

myCtx.deleteDatabase(DATABASE_NAME); 

dove myCtx è il contesto attuale, si dovrebbe non essere nullo.

Per eliminare una riga:

db.delete("'" + DBNAME+ "'", "Key" + "=" + rowID, null); 

Answer 3

SQLiteOpenHelper.getWritableDatabase può ottenere la classe SQLiteDatabase, SQLiteDatabase.delete (String table, String whereClause, String[] whereArgs) possibile eliminare tavolo.

se si desidera eliminare database, è possibile diretto eliminare il file di database, il percorso:

/data/data/package_name/databases/db_name