Checkbox from datatable not handling checked event

In my page i am populating a GridView from code behind by setting the source a custom Datatable that i compile from an XML file, in this way i write the columns header and the rows title. And this works fine, so i am adding checkboxes in the cells while adding the columns in this way:

            DataTable dt = new DataTable();
        dt.Columns.Add(" ");
        foreach (XmlNode xns in doc.DocumentElement.ChildNodes[0])
        {
            foreach (XmlNode xn in xns)
            {
                string tagName = xn.Name;

                dt.Rows.Add(tagName);
            }

        } 

        dt.Columns.Add("Mattina Turno 1", typeof(bool)); //this adds the checkbox
        dt.Columns.Add("Mattina Turno 2", typeof(bool)); 
        dt.Columns.Add("Pomeriggio", typeof(bool)); 

        GridView1.DataSource = dt;
        GridView1.DataBind();

I am enabling each checkbox in my Gridview RowDataBound in this way:

 for (int i = 0; i < e.Row.Cells.Count;i++)
        {
            if (e.Row.Cells[i].GetType() == typeof(System.Web.UI.WebControls.DataControlFieldCell))
            {

            TableCell tc = e.Row.Cells[i];
            if (tc.Controls.Count > 0)
                {
                CheckBox cb = (CheckBox)tc.Controls[0];
                    if (cb != null)
                    { 
                        cb.Enabled = true;
                        colonna = ((GridView)sender).HeaderRow.Cells[i].Text;
                        riga = e.Row.Cells[0].Text;
                        cb.CausesValidation = false;
                        cb.ID = riga + " " + colonna;
                        cb.ToolTip = riga + " " + colonna;
                        cb.AutoPostBack = true; 
                        cb.CheckedChanged += new EventHandler(Cb_CheckedChanged);
                    } 

                    }  
                }
            }
        }

But when i try to handle the check event of the checkbox nothing happens. The checkchanged should call Cb_CheckedChanged but nothing happens.

this is Cb_CheckChanged:

        private void Cb_CheckedChanged(object sender, EventArgs e)
    {
        Cliccato.Text = ((CheckBox)sender).ID.ToString();
        System.Diagnostics.Debug.Write(((CheckBox)sender).ToolTip);
    }

Please Help me, i really need your help!