You need to bind data to GridView Control with below code -
GridView1.DataSource = "YOUR_DATASOURCE";
GridView1.DataBind();
Also, you have set
AutoGenerateColumns="False"
for your gridview control so if you need to wrap any logic/functionality around your code before binding you need to implement it like -
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
TextBox textBoxControl = e.Row.FindControl("TextBox1") as TextBox;
textBoxControl.Text = "YOUR_DB_VALUE_FOR_TEXTBOX_TO_ASSIGN";
}
}