private void Button2_Click(object sender, EventArgs e)
        {
            try
            {
                Customer customerToDelete = new Customer
                {
                    CustomerID = Convert.ToInt32(listView1.SelectedItems[0].SubItems[1].Text),
                    Name       = listView1.SelectedItems[0].SubItems[2].Text,
                    Surname    = listView1.SelectedItems[0].SubItems[3].Text,
                    Phone      = listView1.SelectedItems[0].SubItems[4].Text,
                    Address    = listView1.SelectedItems[0].SubItems[5].Text
                };

                var sorgu = DalCustomer.CUD(customerToDelete, System.Data.Entity.EntityState.Deleted);

                if (sorgu)
                {
                    GuncelleMusteriler();
                    MessageBox.Show("Müşteri silindi.", "İşlem Başarılı", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }
            }
            catch (Exception)
            {
                MessageBox.Show("Müşteri seçilmedi.", "Hata", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }
        }
        private void Button3_Click(object sender, EventArgs e)
        {
            try
            {
                var anyEmptyArea = EmptyTextBoxControl(groupBox3);
                if (anyEmptyArea)
                {
                    MessageBox.Show("Eksik bilgi girdiniz.", "Hata", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                }
                else
                {
                    Customer newCustomer = new Customer
                    {
                        Name    = textBox1.Text,
                        Surname = textBox2.Text,
                        Phone   = textBox3.Text,
                        Address = textBox4.Text
                    };

                    var sorgu = DalCustomer.CUD(newCustomer, System.Data.Entity.EntityState.Added);

                    if (sorgu == true)
                    {
                        textBox1.Clear();
                        textBox2.Clear();
                        textBox3.Clear();
                        textBox4.Clear();

                        GuncelleMusteriler();
                        MessageBox.Show("Yeni müşteri eklendi.", "İşlem Başarılı", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }
                    else
                    {
                        MessageBox.Show("Müşteri ekleme başarısız.", "Hata", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                    }
                }
            }
            catch (Exception)
            {
                MessageBox.Show("Eksik bilgi girdiniz.", "Hata", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }
        }
        private void Button4_Click(object sender, EventArgs e)
        {
            try
            {
                var anyEmptyArea = EmptyTextBoxControl(groupBox4);
                if (anyEmptyArea)
                {
                    MessageBox.Show("Eksik bilgi girdiniz.", "Hata", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                }
                else
                {
                    Customer customerToUpdate = new Customer
                    {
                        CustomerID = Convert.ToInt32(textBox27.Text),
                        Name       = textBox8.Text,
                        Surname    = textBox7.Text,
                        Phone      = textBox6.Text,
                        Address    = textBox5.Text
                    };

                    var sorgu = DalCustomer.CUD(customerToUpdate, System.Data.Entity.EntityState.Modified);

                    if (sorgu)
                    {
                        textBox5.Clear();
                        textBox6.Clear();
                        textBox7.Clear();
                        textBox8.Clear();

                        GuncelleMusteriler();
                        MessageBox.Show("Müşteri bilgileri güncellendi.", "İşlem Başarılı", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }
                }
            }
            catch (Exception)
            {
                MessageBox.Show("Eksik bilgi girdiniz.", "Hata", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }
        }