gridview中判断隐藏还是现实

  <asp:TemplateField HeaderText="呼出" HeaderStyle-Width="60px" HeaderStyle-HorizontalAlign="Center" ItemStyle-HorizontalAlign="Center">
            <ItemTemplate>
                <a href="javascript:void(0)" class="btn" onclick="event.cancelBubble=true;CallOutClient('<%# Eval("C_Tel") %>','<%# Eval("C_ClientID") %>');"><span class="in"><input type="button" value="呼出"/></span></a>
                <a id="lnkCallExt" style='display:<%# Eval("C_Extension").ToString()==""?"none":"block"  %>' href="javascript:void(0)" class="btn" onclick="event.cancelBubble=true;CallOutClient('<%# Eval("C_Tel") %>','<%# Eval("C_ClientID") %>');"><span class="in"><input type="button" value="呼出分机"/></a>
            </ItemTemplate>
    </asp:TemplateField>
    </Columns>