populating textbox from database using gridviewrow selection

I think this code solve your problem.......
I have customize own code please see this code and also see attached application

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;


public partial class Demo : System.Web.UI.Page
{
    SqlConnection con = new SqlConnection("Data source=PRITI-PC; initial catalog=test;uid=sa;pwd=a");
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindGrid();
        }


    }






    private void BindGrid()
    {
        DataTable _dt = new DataTable();
        SqlDataAdapter ad = new SqlDataAdapter("Select id,Name,salary from mytable", con);
        ad.Fill(_dt);
        gdvData.DataSource = _dt;
        gdvData.DataBind();
    }
    ///

    /// this is gridview Select button Event.
    ///

    ///
    ///
    protected void btnselect_Click(object sender, EventArgs e)
    {
        GridViewRow gridViewRow = (GridViewRow)(sender as Control).Parent.Parent;


        //using this line find index of clickd row.
        int index = gridViewRow.RowIndex;


        //using Below wrriten code you can get the id(primary key column value) of selected row.
        //you can store primary key column value in DataKeyNames property of gridview and get this value
        //using this code and then using the primary key column value you can get remaining column value from
        //database.
        string id = gdvData.DataKeys[index]["id"].ToString();
        Getdatafromdatabase(id);


        //Then populate your textbox with gridview selected row data.
        txtName.Text = gdvData.Rows[index].Cells[1].Text.ToString();
        txtSalary.Text = gdvData.Rows[index].Cells[2].Text.ToString();




    }
    ///

    /// In this code i get remaining column value  from database when i clicked on gridview row.
    ///

    private void Getdatafromdatabase(string id)
    {
        DataTable _dt = new DataTable();
        SqlDataAdapter ad = new SqlDataAdapter("Select id,Name,salary,age from mytable where id='" + id + "'", con);
        ad.Fill(_dt);
        txtage.Text = _dt.Rows[0]["age"].ToString();


    }
}

Please don't forget to mark as answer if this post helps you.

also, here's my code in asp.net (I do have a DatakeyName="vinno") which is the basis on the string rowID = grdvwSearch.SelectedValue.ToString();

Follow this link

http://weblogs.asp.net/gurusarkar/archive/2010/09/22/get-gridview-rowindex-upon-button-click.aspx

And See attached aplication:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;


public partial class Demo : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindGrid();
        }


    }


    ///

    /// this method data for binding grid.
    ///

    ///
    private DataTable dataforbindgrid()
    {
        DataTable _dt = new DataTable();
        _dt.Columns.Add("Name");
        _dt.Columns.Add("Age");
        _dt.Rows.Add("Priti", "23");
        _dt.Rows.Add("priya", "24");
        _dt.Rows.Add("anu", "20");
        _dt.Rows.Add("sikha", "25");
        return _dt;
    }




    private void BindGrid()
    {
        gdvData.DataSource = dataforbindgrid();
        gdvData.DataBind();
    }
    ///

    /// this is gridview Select button Event.
    ///

    ///
    ///
    protected void btnselect_Click(object sender, EventArgs e)
    {


        GridViewRow gridViewRow = (GridViewRow)(sender as Control).Parent.Parent;
        //using this line find index of clickd row.
        int index = gridViewRow.RowIndex;
        //Then populate your textbox with gridview selected row data.
        txtAge.Text = gdvData.Rows[index].Cells[1].Text.ToString();
        txtName.Text = gdvData.Rows[index].Cells[2].Text.ToString();




    }
}