Asp.net 通过刷新页面防止隐藏网格

我用c#在asp.net中制作了一个表单，其中网格视图和数据显示正确，但我也在表单上制作了“插入-删除”按钮，当我单击“插入”按钮时，页面被刷新，网格视图无法看到如何解决此问题并防止隐藏网格`

<table style ="margin-left:50px;">
     <tr>                
        <td style ="width:10px;">
         <asp:Button UseSubmitBehavior="true" ID="bttnadd" runat="server" Text="Add" style ="width:60px; background-color:azure" OnClick="bttnadd_Click" CommandName="bttnadd" OnClientClick ="showgrid()"/> </td>
        <td colspan ="2;">
          <asp:Button ID="bttndelete" runat="server" Text="Delete" style ="width:60px;background-color:azure" /> </td >

        <td colspan ="0;">
          <asp:Button ID="Bttnupdate" runat="server" Text="update" style ="width:60px; background-color:azure" /> </td>
        <td class="auto-style6">
          <asp:Button ID="Bttnreset" runat="server" Text="Reset" style ="width:60px; background-color:azure" /> 
        </td>
       </tr>
 </table>


 <asp:GridView ID="GridView1" runat="server" AllowPaging="True" 
               AllowSorting="True" AutoGenerateColumns="False" 
               DataKeyNames="category_id" DataSourceID="SqlDataSource1" 
               HorizontalAlign="Right" PageSize="5" 
               EnablePersistedSelection="True" ViewStateMode="Enabled" 
               Width="1px" CellPadding="4" Font-Size="Medium" 
               ForeColor="#333333" GridLines="None" 
               OnSelectedIndexChanged="GridView1_SelectedIndexChanged1">
     <AlternatingRowStyle HorizontalAlign="Right" VerticalAlign="Top" 
               BackColor="White" />
        <Columns>
            <asp:CommandField ShowDeleteButton="True" ShowEditButton="True" ShowSelectButton="True"   />
            <asp:BoundField DataField="category_id" HeaderText="category_id" InsertVisible="False" ReadOnly="True" SortExpression="category_id" />
            <asp:BoundField DataField="category_name" HeaderText="category_name" SortExpression="category_name" />
            <asp:BoundField DataField="category_description" HeaderText="category_description" SortExpression="category_description" />
        </Columns>
        <FooterStyle BackColor="#990000" Font-Bold="True" ForeColor="White" />
        <HeaderStyle BackColor="#990000" Font-Bold="True" ForeColor="White" />
        <PagerSettings Mode="NextPreviousFirstLast" />
        <PagerStyle HorizontalAlign="Center" BackColor="#FFCC66" ForeColor="#333333" />

        <RowStyle HorizontalAlign="Right" BackColor="#FFFBD6" ForeColor="#333333" />
        <SelectedRowStyle BackColor="#9966FF" Font-Bold="True" ForeColor="Navy" />
        <SortedAscendingCellStyle BackColor="#FDF5AC" />
        <SortedAscendingHeaderStyle BackColor="#4D0000" />
        <SortedDescendingCellStyle BackColor="#FCF6C0" />
        <SortedDescendingHeaderStyle BackColor="#820000" />
    </asp:GridView>


    <asp:GridView ID="GridView1" runat="server" AllowPaging="True" 
                  AllowSorting="True" AutoGenerateColumns="False" 
                  DataKeyNames="category_id" DataSourceID="SqlDataSource1" 
                  HorizontalAlign="Right" PageSize="5" 
                  EnablePersistedSelection="True" ViewStateMode="Enabled" 
                  Width="1px" CellPadding="4" Font-Size="Medium" 
                  ForeColor="#333333" GridLines="None" 
                  OnSelectedIndexChanged="GridView1_SelectedIndexChanged1">
     <AlternatingRowStyle HorizontalAlign="Right" VerticalAlign="Top" 
                          BackColor="White" />
        <Columns>
            <asp:CommandField ShowDeleteButton="True" ShowEditButton="True" ShowSelectButton="True"   />
            <asp:BoundField DataField="category_id" HeaderText="category_id" InsertVisible="False" ReadOnly="True" SortExpression="category_id" />
            <asp:BoundField DataField="category_name" HeaderText="category_name" SortExpression="category_name" />
            <asp:BoundField DataField="category_description" HeaderText="category_description" SortExpression="category_description" />
        </Columns>
        <FooterStyle BackColor="#990000" Font-Bold="True" ForeColor="White" />
        <HeaderStyle BackColor="#990000" Font-Bold="True" ForeColor="White" />
        <PagerSettings Mode="NextPreviousFirstLast" />
        <PagerStyle HorizontalAlign="Center" BackColor="#FFCC66" ForeColor="#333333" />

        <RowStyle HorizontalAlign="Right" BackColor="#FFFBD6" 
                  ForeColor="#333333" />
        <SelectedRowStyle BackColor="#9966FF" Font-Bold="True" 
                  ForeColor="Navy" />
        <SortedAscendingCellStyle BackColor="#FDF5AC" />
        <SortedAscendingHeaderStyle BackColor="#4D0000" />
        <SortedDescendingCellStyle BackColor="#FCF6C0" />
        <SortedDescendingHeaderStyle BackColor="#820000" />
    </asp:GridView>

---

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请从CS页面共享页面加载事件。我已将asp.net中formaspx页面的页面加载事件与c sharp共享。如何从css共享它？