How to add Textbox to gridView

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ASP.NET

Hello Everyone

Actually I Want to add TextBox to gridview.

I did this

protected void Page_Load(object sender,  EventArgs e)
{
 GridView1.DataSource = Db.FillDataGrid("Select colName1, 1+1 as translate, .... ", " TableName ", GridView1);
 GridView1.DataBind();
 InitControls();
}

private void InitControls()
    {
        try
        {
            for (int j = 0; j < 1; j++)
            {
                for (int i = 2; i < 30; i += 2)
                {
                     TextBox textbox = new TextBox();
                    textbox.ID = "text" + (j+1);
                    textbox.Width = 200;
                    GridView1.Rows[j].Cells[i].Controls.Add(textbox);
                }
            }
        }
        catch (Exception e)
        {
           // ScriptManager.RegisterStartupScript(this.UpdatePanel1, UpdatePanel1.GetType(), "scriptname", "alert('"+e.Message+"')", true);
        }
        
    }

when I get TextBox

protected void Button1_Click(object sender, EventArgs e)
    {
        TextBox text = ((TextBox) GridView1.Rows[0].Cells[2].FindControl("text1"));

        string f = text.Text;
        return;
    }

give me Error Message TextBox

[NullReferenceException: Object reference not set to an instance of an object.]
   _Default.Button1_Click(Object sender, EventArgs e) in c:\Users\Aghadeer\Desktop\(Ammars' Computer)\Collection\CSS Template\EditableWesbsite\Default.aspx.cs:132
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +9553594
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +103
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +35
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1724

if there is another way can you tell me

sorry for English