C# Gridview问题对象不能从DBNull转换为其他类型

嗨，我正在尝试在gridview中显示购物车详细信息 在我的gridview中，我有一个名为imagedelete的图像按钮，如果我点击这个记录，它将被删除。该功能运行良好。在RowDataBound事件的同一个gridview中，我还计算一列的总量并将其显示在页脚中，但当我删除一条记录时，它会给出一些异常

下面是gridview的代码 受保护的void gvDetails_RowDataBound（对象发送方，GridViewRowEventArgs e） {

        if (e.Row.RowType == DataControlRowType.DataRow)
            {
                total += Convert.ToInt32(DataBinder.Eval(e.Row.DataItem, "Total"));
            }
            if (e.Row.RowType == DataControlRowType.Footer)
            {
                Label lblamount = (Label)e.Row.FindControl("lblTotal");
                if (total != 0)
                {
                    lblamount.Text = total.ToString();
                }
                else
                {
                    lblamount.Visible = false;
                }
            }
        //}
    }

        int userid = Convert.ToInt32(gvDetails.DataKeys[e.RowIndex].Values["CartId"].ToString());


        con.Open();

        SqlCommand cmd = new SqlCommand("delete from tblCart where CartId='" + userid + "'", con);


        int result = cmd.ExecuteNonQuery();
        con.Close();
        if (result == 1)
        {
            Response.Write("Success");
            BindGridView(visitorId);

        }
    }

  void BindGridView(string visitor)
    {
        cmd = new SqlCommand("select c.CartId,c.EmailId, c.ProductId,p.ProductName,p.ProductImage,v.VariantId,v.VariantName,c.Quantity,v.ProductCost,(v.ProductCost*c.Quantity) as Total from tblCart as c join tblProducts as p on c.ProductId=p.ProductId join tblVariant as v on c.VariantId=v.VariantId where c.EmailId='" + visitor + "'", con);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        con.Close();
        if (ds.Tables[0].Rows.Count > 0)
        {
            gvDetails.DataSource = ds;
            gvDetails.DataBind();
        }
        else
        {
            ds.Tables[0].Rows.Add(ds.Tables[0].NewRow());
            gvDetails.DataSource = ds;
            gvDetails.DataBind();
            int columncount = gvDetails.Rows[0].Cells.Count;
            gvDetails.Rows[0].Cells.Clear();
            gvDetails.Rows[0].Cells.Add(new TableCell());
            gvDetails.Rows[0].Cells[0].ColumnSpan = columncount;
            gvDetails.Rows[0].Cells[0].Text = "No Records Found";
        }
    }

受保护的void gvDetails\u行删除（对象发送方，GridViewDeleteEventArgs e） {

        if (e.Row.RowType == DataControlRowType.DataRow)
            {
                total += Convert.ToInt32(DataBinder.Eval(e.Row.DataItem, "Total"));
            }
            if (e.Row.RowType == DataControlRowType.Footer)
            {
                Label lblamount = (Label)e.Row.FindControl("lblTotal");
                if (total != 0)
                {
                    lblamount.Text = total.ToString();
                }
                else
                {
                    lblamount.Visible = false;
                }
            }
        //}
    }

        int userid = Convert.ToInt32(gvDetails.DataKeys[e.RowIndex].Values["CartId"].ToString());


        con.Open();

        SqlCommand cmd = new SqlCommand("delete from tblCart where CartId='" + userid + "'", con);


        int result = cmd.ExecuteNonQuery();
        con.Close();
        if (result == 1)
        {
            Response.Write("Success");
            BindGridView(visitorId);

        }
    }

  void BindGridView(string visitor)
    {
        cmd = new SqlCommand("select c.CartId,c.EmailId, c.ProductId,p.ProductName,p.ProductImage,v.VariantId,v.VariantName,c.Quantity,v.ProductCost,(v.ProductCost*c.Quantity) as Total from tblCart as c join tblProducts as p on c.ProductId=p.ProductId join tblVariant as v on c.VariantId=v.VariantId where c.EmailId='" + visitor + "'", con);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        con.Close();
        if (ds.Tables[0].Rows.Count > 0)
        {
            gvDetails.DataSource = ds;
            gvDetails.DataBind();
        }
        else
        {
            ds.Tables[0].Rows.Add(ds.Tables[0].NewRow());
            gvDetails.DataSource = ds;
            gvDetails.DataBind();
            int columncount = gvDetails.Rows[0].Cells.Count;
            gvDetails.Rows[0].Cells.Clear();
            gvDetails.Rows[0].Cells.Add(new TableCell());
            gvDetails.Rows[0].Cells[0].ColumnSpan = columncount;
            gvDetails.Rows[0].Cells[0].Text = "No Records Found";
        }
    }

下面是我试图删除记录时遇到的错误 对象不能从DBNull强制转换为其他类型。在此行 总计+=转换为32（datainder.Eval（如Row.DataItem，“总计”）

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有人能帮我解决这个问题吗。

您的数据库字段包含空值，因此不能转换为其他类型（在您的实例中为Int）。请阅读。

您好，我引用您建议的链接，并添加这行代码f（DBNull.Value.Equals（sender）| sender==NULL |然后集成我的行绑定代码来计算列总数。如果（！DBNull.Value.Equals（datainder.Eval（e.row.DataItem，“total”））那么我仍然有相同的问题