无法将类型为“System.Web.UI.LiteralControl”的对象强制转换为类型“System.Web.UI.WebControls.TextBox”
代码如下： protected void gvMark_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        int i = e.RowIndex;
        string markId = gvMark.DataKeys[i].Value.ToString();
        string nd = ((TextBox)(gvMark.Rows[i].Cells[1].Controls[0])).Text.ToString();
        string mc = ((TextBox)(gvMark.Rows[i].Cells[2].Controls[0])).Text.ToString();
        string bd = ((TextBox)(gvMark.Rows[i].Cells[3].Controls[0])).Text.ToString();
        string qy = ((TextBox)(gvMark.Rows[i].Cells[4].Controls[0])).Text.ToString();
        string gn = ((TextBox)(gvMark.Rows[i].Cells[5].Controls[0])).Text.ToString();
        string yz = ((TextBox)(gvMark.Rows[i].Cells[6].Controls[0])).Text.ToString();
        string gj = ((TextBox)(gvMark.Rows[i].Cells[7].Controls[0])).Text.ToString();
        try
        {
            WebErp.DataBase dbms = new WebErp.DataBase();
            string upstr = "update sale set nd='" + nd + "', mc='" + mc + "', bd='" + bd + "', qy='" + qy + "', gn='" + gn + "', yz='" + yz + "', gj='" + gj + "' where bh=" + int.Parse(markId);
            dataBindDataGrid();//重新绑定gvMark的数据
            Page.ClientScript.RegisterStartupScript(Page.GetType(), "", "<script language='Javascript'>alert('更新成功！');</script>");

        }
        catch
        {
            Page.ClientScript.RegisterStartupScript(Page.GetType(), "", "<script language='Javascript'>alert('更新失败！');</script>");
            return;


        }
        this.gvMark.EditIndex = -1;
        dataBindDataGrid();
    }

string nd = gvMark.Rows[i].Cells[1].Text.ToString();