Validation for dynamic gridview cells

This way:

protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            this.GetTable("Customers");
        }
        else
        {
            AddControls();

        }
    }
 private void AddControls()
    {
        int cellCount = this.GridView1.Rows[0].Cells.Count;
        int rowsCount = this.GridView1.Rows.Count;
        this.GridView1.Rows[rowsCount - 1].Cells[0].Controls.RemoveAt(0);
        Button btn = new Button();
        btn.Attributes.Add("runat", "server");
        btn.ID = "btnInsert";
        btn.Text = "Insert";
        btn.OnClientClick = "Insert();";
        this.GridView1.Rows[rowsCount - 1].Cells[0].Controls.Add(btn);
        for (int i = 1; i < 3; i++)
        {
            Label label = new Label();
            label.ID = "lblNewLabel" + i.ToString();
            label.Attributes.Add("runat", "server");
            label.Text = "add your Randome Value";
            this.GridView1.Rows[rowsCount - 1].Cells[i].Controls.Add(label);
        }

        for (int j = 3; j < cellCount; j++)
        {
            //here i am adding a control.
            TextBox textBox = new TextBox();
            textBox.ID = "txtDynamicText" + j.ToString();
            textBox.Attributes.Add("runat", "server");
            textBox.CssClass = "Color";
            textBox.Text = Request.Form[textBox.UniqueID];
            this.GridView1.Rows[rowsCount - 1].Cells[j].Controls.Add(textBox);
        }
    }
 protected void Save(object sender, EventArgs e)
    {
        int cellCount = this.GridView1.Rows[0].Cells.Count;
        int rowCount = this.GridView1.Rows.Count - 1;  

        for (int i = 3; i < cellCount - 1; i++)
        {            
            TextBox text = (TextBox)this.GridView1.Rows[rowCount].Cells[i].FindControl("txtDynamicText" + i.ToString());
        }
    }

Image:

Thank You.