using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;

namespace WindowsFormsApp13
{
    class sqlBaglantisiSinifi
    {

        public SqlConnection baglantiMetodu() // tanımlamış olduğun metot geri değer döndüren bir metot
        {
         SqlConnection baglan = new SqlConnection (@"Data Source=FP-BIDB-21\SQLEXPRESS;Initial Catalog=ogrenci;Integrated Security=True");
            baglan.Open();
            return baglan;
        }
    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace WindowsFormsApp13
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            sqlBaglantisiSinifi baglantiNesnesi = new sqlBaglantisiSinifi(); // nesne türetiyoruz
            SqlDataAdapter da = new SqlDataAdapter("select * from kisiler", baglantiNesnesi.baglantiMetodu());
            DataSet ds = new DataSet();
            da.Fill(ds);
            dataGridView1.DataSource = ds.Tables[0];

        }
    }
}