In edit mode in gridview everytime ihave to select dropdownlist otherwise its store first value

<asp:GridViewID="GVTrouserJobWork"runat="server"  AutoGenerateColumns="False"CssClass="Gridview"HeaderStyle-BackColor="#4B6D9D"DataKeyNames="TrouserJobID"

OnRowCancelingEdit="GVTrouserJobWork_RowCancelingEdit"OnRowDeleting="GVTrouserJobWork_RowDeleting"

OnRowEditing="GVTrouserJobWork_RowEditing"OnRowUpdating="GVTrouserJobWork_RowUpdating">

<Columns>

<asp:TemplateFieldHeaderText="StyleNo"

<asp:LabelID="lblStyleNo"runat="server"Text='<%#Eval("StyleNo") %>'/>

<asp:DropDownList Width="60px"  DataSource='<%# GetStyleNo() %>' DataTextField="StyleNo"

</EditItemTemplate>

<ItemTemplate>

<asp:LabelID="lblStyleNo1"runat="server"Text='<%#Eval("StyleNo") %>'/>

</ItemTemplate>

</asp:TemplateField>

</Columns>

</asp:GridView>

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DataSetGetStyleNo() {

SqlConnectionmyConnection =newSqlConnection(ConfigurationManager.ConnectionStrings["constring"].ToString());

SqlCommandcmd =newSqlCommand();

"StleMasterList";

CommandType.StoredProcedure;

SqlDataAdapterad =newSqlDataAdapter("StleMasterList", myConnection);

//SelectDDCompanyName

DataSetds =newDataSet();

"StleMasterList");

returnds;

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StleMasterList = Select StyleNo from Stylemaster

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protectedvoidGVTrouserJobWork_RowUpdating(objectsender,GridViewUpdateEventArgse)

intTrouserOrderID =Convert.ToInt32(GVTrouserOrderDetail.DataKeys[e.RowIndex].Value.ToString());

DropDownListStyleNo = (DropDownList)GVTrouserOrderDetail.Rows[e.RowIndex].FindControl("StyleNo");

SqlCommandcmd =newSqlCommand("update TrouserOrders set StyleNo='"+ StyleNo.SelectedValue.ToString() + "'where TrouserOrderID="+ TrouserOrderID, con);

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Actually I get dropdown in editmode but when without selecting dropdownlist if I update it it select first value of dropdown list.

if have two dropdownlist in gridview and I want to update only one I cant do this every time I have to select bothdropdownlist .