Display data from a TextBox to a GridView without saving the data to the database

You have to persists the data between postbacks,

You have many options here: by Session, ViewState, Cache and some other.

protected void Page_Load(object sender, EventArgs e){    if (Page.IsPostback)    {         dt = Session["data_table"] as DataTable;    }}protected void btnTextDisplay_Click(object sender, EventArgs e){     if (dt == null)     {          dt = new DataTable();          DataColumn dc1 = new DataColumn("Name");          DataColumn dc2 = new DataColumn("City");          dt.Columns.Add(dc1);          dt.Columns.Add(dc2);   
     }     DataRow dr = dt.NewRow();     dr[0] = txtName.Text;     dr[1] = txtCity.Text;     dt.Rows.Add(dr);     gvDisplay.DataSource = dt;     gvDisplay.DataBind();     Session["data_table"] = dt;}