DropDownList不存储值

Question

I am working on an e-commerce app and the problem is in showing the quantity of items purchased. The DropDownList shows the option to change quantity, it is in a gridview and it has a selectedindexchanged event. The event code works fine but when there are two(or more) products and we change the quantity of one row and then change the other rows's quantity, the previous row quantity is set back to default that is "1" while total price column shows the multiplication of price and quanity that we set to the DropDownList.

My DropDownList code:

<asp:TemplateField HeaderText="Qty">
                    <EditItemTemplate>
                        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
                    </EditItemTemplate>
                    <ItemTemplate>
                        <asp:DropDownList ID="ddlQty" runat="server" AutoPostBack="True" 
                            onselectedindexchanged="ddlQty_SelectedIndexChanged">
                            <asp:ListItem>1</asp:ListItem>
                            <asp:ListItem>2</asp:ListItem>
                            <asp:ListItem>3</asp:ListItem>
                            <asp:ListItem>4</asp:ListItem>
                            <asp:ListItem>5</asp:ListItem>
                        </asp:DropDownList>
                    </ItemTemplate>
                </asp:TemplateField>

My C# code for the SelectedIndexChanged and GridView RowDataBoundevent:

protected void ddlQty_SelectedIndexChanged(object sender, EventArgs e)
    {
        DropDownList ddlQty =(DropDownList)sender;
        int rowindex = int.Parse(ddlQty.Attributes["rowindex"].ToString());
        ViewState["index"] = rowindex;
        ViewState["I"] = ddlQty.SelectedValue;

        decimal price = Convert.ToDecimal(ds.Tables[0].Rows[rowindex]["Price"].ToString());
        decimal totalprice = price * Convert.ToInt32(ddlQty.SelectedValue);
        ds.Tables[0].Rows[rowindex]["TotalPrice"] = totalprice;
        GridView1.DataSource = ds;
        GridView1.DataBind();
        ds.Tables[1].Rows[0]["TotalPrice"] = decimal.Parse(ds.Tables[1].Rows[0]["TotalPrice"].ToString()) + totalprice - Convert.ToDecimal(ds.Tables[0].Rows[rowindex]["Price"].ToString());
        GridView1.FooterRow.Cells[2].Text = "Total Amount =";
        GridView1.FooterRow.Cells[3].Text = ds.Tables[1].Rows[0]["TotalPrice"].ToString();
    }
    protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            DropDownList ddl = (DropDownList)e.Row.FindControl("ddlQty");
            ddl.Attributes.Add("rowindex", e.Row.RowIndex.ToString());
            if (ViewState["index"] != null)
            {
                if (e.Row.RowIndex.ToString() == ViewState["index"].ToString())
                {
                    ddl.SelectedValue = ViewState["I"].ToString();
                }
            }

        }
    }

I am attaching an image also to make it more clear.

Answer 1

I think your grid is binding on each postback made by dropdownlist, so changing one value will overwrite the formerly stored value in VS. You should try storing these values as a list, appending changes to it instead of replacing it each time.

IMHO, anyway, I would go by setting AutoPostBack properties to false, and updating row calculations client-side, then validating on server side on submit.