使用 Sqiltehelper 如何删除表格和数据库？

Question

我创建了一个类名称是 DatabaseHandler，继承 SQLiteOpenHelper。我想通过按钮点击删除数据库或表格。如何处理调用函数时传递的参数？

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);
}
// 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

你可以在按钮点击事件中创建一个 DatabaseHandler 对象，然后调用该对象的删除数据库或表格的方法。例如，要删除整个数据库，可以在按钮点击事件中执行以下操作：

DatabaseHandler db = new DatabaseHandler(context);
db.getWritableDatabase().execSQL("DROP DATABASE " + DATABASE_NAME);

要删除表格，可以使用下面这个：

db.getWritableDatabase().execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);