停止下拉列表SelectedIndexChanged事件触发的FormView命令

在edittitemtemplate中有一个下拉列表。Dropdownlist onSelectedIndexChanged事件在我想要的变化时触发。但是，当我提交表单时，它也会触发。

* * * * * * * *更新 ************根据Saechel下面的评论，我开始进一步调查。这里它描述了它是可以做到的。http://blog.programmingsolution.net/net-windows-application/selectionchangecommitted-and-selectedindexchanged-events-system-nullreferenceexception-while-closing-windows-form/但是，我试过了，它甚至没有触发事件。我检查了http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.dropdownlist(v=vs.110).aspx，他们没有列出事件。

我的目标是让用户输入总量的百分比或实际吨的值，然后来回切换。将插入到数据库中的最终值将以吨为单位。

我想:a)不触发"onSelectedIndexChanged"事件b)如何确定我是否在相同的索引上，并有一个if语句跳过一切c)一种我不知道的更好的方法。

我试着通过ViewState验证下拉菜单的当前索引，跳过代码，如果它是相同的，但找不到值。也许能帮我算出这个值?到处找都找不到该怎么做。我尝试了:' var vs = ViewState["ddl_units"].ToString();和其他一些变化，因为我需要通过FindControl

找到控件

. aspx:

<asp:Panel ID="pnlRecycledMaterialsReceivedForm" runat="server" Visible="false">
    <asp:FormView ID="fvAddRecycledMaterialsReceived" runat="server" SkinID="annualReportFormview" EnableViewState="false"
        HeaderText="Selected Recycled Materials Received Detail" DataKeyNames="RecycleDetailId" DefaultMode="Insert"
        DataSourceID="odsRecycledMaterialsReceivedDetail" OnDataBound="fvAddRecycledMaterialsReceived_DataBound" 
        OnItemCommand="fvAddRecycledMaterialsReceived_ItemCommand" OnItemInserted="fvAddRecycledMaterialsReceived_ItemInserted"
        OnItemUpdated="fvAddRecycledMaterialsReceived_ItemUpdated" OnItemDeleted="fvAddRecycledMaterialsReceived_ItemDeleted">
        <EditItemTemplate>
            <asp:TextBox ID="tbxRecycledTotalWasteQuantity" runat="server" Text='<%# Bind("TotalWasteQuantity") %>' Width="64px"></asp:TextBox>
            <asp:TextBox ID="tbxRecycledWasteCommercialQuantity" runat="server" Text='<%# Bind("CommercialQuantity") %>' Width="64px"></asp:TextBox>
            <asp:TextBox ID="tbxRecycledWasteResidentialQuantity" runat="server" Text='<%# Bind("ResidentialQuantity") %>' Width="64px"></asp:TextBox>
            <asp:DropDownList ID="ddl_Units" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl_Units_SelectedIndexChanged">
                <asp:ListItem Value="" Text="" Enabled="false" />
                <asp:ListItem Text="Tons" Value="1" />
                <asp:ListItem Text="Percent" Value="9" />
            </asp:DropDownList>
            <asp:LinkButton ID="lbtnWasteReceivedUpdate" runat="server" Text="Update" CommandName="Update"
                ValidationGroup="RecycledWasteReceivedDetail" Font-Bold="True" />&nbsp;
            <asp:LinkButton ID="lbtnWasteReceivedInsertCancel" runat="server" Text="Cancel" CausesValidation="False" CommandName="Cancel" />
        </EditItemTemplate>
    </asp:FormView>
</asp:Panel>

cs:

protected void ddl_Units_SelectedIndexChanged(object sender, EventArgs e)
{
    TextBox tbxRecycledTotalWasteQuantity = (TextBox)fvAddRecycledMaterialsReceived.FindControl("tbxRecycledTotalWasteQuantity");
    TextBox tbxRecycledWasteResidentialQuantity = (TextBox)fvAddRecycledMaterialsReceived.FindControl("tbxRecycledWasteResidentialQuantity");
    var d_TotalWasteQuantity = Convert.ToDecimal(tbxRecycledTotalWasteQuantity.Text);
    ResidentialQuantity = Convert.ToDecimal(tbxRecycledWasteResidentialQuantity.Text);
    DropDownList ddl_units = (DropDownList)fvAddRecycledMaterialsReceived.FindControl("ddl_units");
    if (ddl_units.SelectedIndex.ToString() == "2")
    {
        //2 = percent
        //Take tb value and convert to percent
        //300/700 * 100
        tbxRecycledWasteResidentialQuantity.Text = ((ResidentialQuantity / d_TotalWasteQuantity) * 100).ToString();
        //ResidentialQuantity = ResidentialQuantity * (d_TotalWasteQuantity / 100);
    }
    else
    {
        //Else 'tons' was chosen. Convert value(%) to tons. 
        //700 * (43/100) = 301
        ResidentialQuantity = d_TotalWasteQuantity * (ResidentialQuantity / 100);
        tbxRecycledWasteResidentialQuantity.Text = ResidentialQuantity.ToString();
        //tbxRecycledWasteResidentialQuantity.Text = "Tons";
    }
}