在UpdatePanel里面添加了一个UserControl，这个用户控件是在MasterPage里面添加的。单击该 UpdatePanl 中的按钮时。整个页面都刷新了。为什么？
母版页：
<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Site.master.cs" Inherits="webasite.SiteMaster" %>
<%@ Register Src="views/uc/_aside.ascx" TagPrefix="uc1" TagName="_aside" %>
<%@ Register Src="views/uc/_page-loader.ascx" TagPrefix="uc1" TagName="_pageloader" %>
<!DOCTYPE html>
<html lang="ar" direction="rtl" dir="rtl" style="direction: rtl">
<!--begin::Head-->
<head>
<base href="">
<meta charset="utf-8" />
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true"></asp:ScriptManager>
<uc1:_pageloader runat="server" id="_pageloader" />
<uc1:_aside runat="server" id="_aside" />
</form>
</body>
</html>
用户控制：_aside.ascx
<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="_aside.ascx.cs" Inherits="cidyai.partials.uc._aside" %>
<%@ Register Src="~/app/views/uc/dashboard.ascx" TagPrefix="uc2" TagName="dashboard" %>
<%@ Register Src="~/app/views/uc/drivers.ascx" TagPrefix="uc1" TagName="drivers" %>
<uc2:dashboard runat="server" ID="dashboard" UpdateMode="Conditional"/>
<uc1:drivers runat="server" id="drivers" UpdateMode="Conditional"/>
用户控制：drivers.ascx
<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="drivers.ascx.cs" Inherits="cidyai.app.views.uc.drivers" %>
<asp:UpdateProgress ID="UpdateProgress1" runat="server">
<ProgressTemplate></ProgressTemplate>
</asp:UpdateProgress>
<form class="form">
<asp:UpdatePanel ID="UpdatePanel1" runat="server" ChildrenAsTriggers="true" UpdateMode="Conditional">
<ContentTemplate>
<asp:TextBox ID="txtFirstName" runat="server" CssClass="form-control form-control-solid" placeholder="Name"></asp:TextBox>
<asp:Button ID="btnSave" CssClass="btn btn-primary mr-2" runat="server" Text="save" OnClick="btnSave_Click" />
</ContentTemplate>
</asp:UpdatePanel>
</form>