Take Template Field Like Below
<asp:DetailsView ID="dvCategory" runat="server" AutoGenerateRows="False"
DataKeyNames="iCategoryID" Width="90%" GridLines="None"
OnItemInserting="dvCategory_ItemInserting"
OnItemUpdating="dvCategory_ItemUpdating"
OnModeChanging="dvCategory_ModeChanging" ondatabound="dvCategory_DataBound" >
<Fields>
<asp:BoundField DataField="iCategoryID" HeaderText="ID" InsertVisible="False" ReadOnly="True" />
<asp:TemplateField HeaderText="Name">
<EditItemTemplate>
<asp:TextBox ID="txtCategoryName" runat="server" Text='<%# Bind("strCategoryName") %>'></asp:TextBox>
<asp:RequiredFieldValidator ID="rfvCategoryName" runat="server" ControlToValidate="txtCategoryName"
Display="Dynamic" ErrorMessage="Name" SetFocusOnError="True">*</asp:RequiredFieldValidator>
</EditItemTemplate>
<InsertItemTemplate>
<asp:TextBox ID="txtCategoryName" runat="server" Text='<%# Bind("strCategoryName") %>'></asp:TextBox>
<asp:RequiredFieldValidator ID="rfvCategoryName" runat="server" ControlToValidate="txtCategoryName"
Display="Dynamic" ErrorMessage="Name" SetFocusOnError="True">*</asp:RequiredFieldValidator>
</InsertItemTemplate>
<ItemTemplate>
<asp:Label ID="lblCategoryName" runat="server" Text='<%# Bind("strCategoryName") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:CommandField ShowEditButton="True" ShowInsertButton="True" />
</Fields>
</asp:DetailsView>