ASP.NET标签为空
[英]ASP.NET label is null
问题描述
I'm trying to make a website with C#. 
我正在尝试使用C＃创建一个网站。 I've a masterpage and there is a DevExpress DateEdit, 4 DevExpress DropDownLists, one button and one label. 我有一个主页，有一个DevExpress DateEdit，4个DevExpress DropDownLists，一个按钮和一个标签。 I've a method like this: 我有一个这样的方法：
protected void dropdownNolar_SelectedIndexChanged(object sender, EventArgs e)
{
var halisaha = (from veri in veriler.tum_halisahalars
where veri.Il == dropdownIl.Text &&
veri.Ilce == dropdownIlce.Text &&
veri.Mahalle == dropdownMahalle.Text &&
veri.No == dropdownNolar.Text
select veri).FirstOrDefault();
if (halisaha != null)
if (halisaha.description != null)
lblDescription.Text = halisaha.description;
}
and masterpage's aspx code: 和母版页的aspx代码：
<%@ Master Language="C#" AutoEventWireup="true" EnableViewState="true" CodeBehind="~/masterPage.master.cs" Inherits="HaliSahaKiralama.masterPage" %>
<%@ Register assembly="DevExpress.Web.v14.1, Version=14.1.6.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" namespace="DevExpress.Web.ASPxEditors" tagprefix="dx" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head id="Head1" runat="server">
<title>Untitled</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="generator" content="Web Page Maker">
<style type="text/css">
#wrapper {
position:relative;
width: 1127px;
margin-top: 20px;
margin-left: auto;
margin-right: auto;
text-align:left;
top: -2px;
left: 55px;
height: 1000px;
background-color:sandybrown;
}
.auto-style1 {
width: 100%;
height: 912px;
border: 5px solid #FFFFFF;
background-color: #66FF33;
}
.auto-style2 {
height: 792px;
}
.auto-style4 {
height: 130px;
border:thick none white;
}
.auto-style5 {
height: 792px;
width: 237px;
}
</style>
</head>
<body style="margin:0px; height: 1093px; background-color:sandybrown" onload="">
<script type="text/javascript" language="javascript">
</script>
<form id="form1" runat="server">
<div id="wrapper">
<table class="auto-style1">
<tr>
<td class="auto-style4" colspan="2" style="background-color:lightseagreen">
<div style="border-style: none; border-color: inherit; border-width: thick; z-index: 1; left: 8px; top: 9px; position: absolute; height: 130px; width: 1111px;">
<img src="hs2.jpg" style="position:absolute; top: 6px; left: 33px; width: 157px;" alt="" />
<dx:ASPxLabel ID="ASPxLabel6" runat="server" Font-Size="36pt" style="z-index: 1; left: 226px; top: 31px; position: absolute; height: 82px; width: 505px" Text="Bamyacılar Halısaha" Theme="Youthful">
</dx:ASPxLabel>
</div>
</td>
</tr>
<tr>
<td class="auto-style5" style="background-color:darkgreen">
<div style="position:absolute; top: -13px; left: 8px; width: 236px; height: 639px; background-color:transparent">
<asp:ContentPlaceHolder ID="ContentPlaceHolder2" runat="server">
<dx:ASPxDateEdit ID="date_editTarih" runat="server" Date="2015-03-24" Font-Size="16pt" style="z-index: 1; left: 18px; top: 196px; position: absolute; height: 21px; width: 170px" Theme="Youthful">
</dx:ASPxDateEdit>
<dx:ASPxLabel ID="ASPxLabel1" runat="server" Font-Size="12pt" style="z-index: 1; left: 18px; top: 165px; position: absolute" Text="İstediğiniz Tarihi Seçiniz:" Theme="Youthful" ForeColor="White">
</dx:ASPxLabel>
<dx:ASPxComboBox ID="dropdownIl" runat="server" style="z-index: 1; left: 18px; top: 280px; position: absolute; height: 29px; width: 170px" Theme="Youthful" OnSelectedIndexChanged="dropdownIl_SelectedIndexChanged1" NullText="İl Seçiniz!">
</dx:ASPxComboBox>
<dx:ASPxLabel ID="ASPxLabel2" runat="server" Font-Size="12pt" style="z-index: 1; left: 18px; top: 478px; position: absolute" Text="Stat Numarasını Seçiniz:" Theme="Youthful" ForeColor="White">
</dx:ASPxLabel>
<dx:ASPxComboBox ID="dropdownIlce" runat="server" style="z-index: 1; left: 17px; top: 353px; position: absolute; height: 29px; width: 170px; bottom: 727px;" Theme="Youthful" OnSelectedIndexChanged="dropdownIlce_SelectedIndexChanged1" NullText="İlçe Seçiniz! ">
</dx:ASPxComboBox>
<dx:ASPxLabel ID="ASPxLabel3" runat="server" Font-Size="12pt" style="z-index: 1; left: 18px; top: 249px; position: absolute" Text="İlinizi Seçiniz:" Theme="Youthful" ForeColor="White">
</dx:ASPxLabel>
<dx:ASPxComboBox ID="dropdownMahalle" runat="server" style="z-index: 1; left: 17px; top: 431px; position: absolute; height: 29px; width: 170px" Theme="Youthful" OnSelectedIndexChanged="dropdownMahalle_SelectedIndexChanged1" NullText="Mahalle Seçiniz! ">
</dx:ASPxComboBox>
<dx:ASPxLabel ID="ASPxLabel4" runat="server" Font-Size="12pt" style="z-index: 1; left: 18px; top: 322px; position: absolute" Text="İlçenizi Seçiniz:" Theme="Youthful" ForeColor="White">
</dx:ASPxLabel>
<dx:ASPxComboBox ID="dropdownNolar" runat="server" style="z-index: 1; left: 18px; top: 510px; position: absolute; height: 29px; width: 170px" Theme="Youthful" OnSelectedIndexChanged="dropdownNolar_SelectedIndexChanged" NullText="Numara Seçiniz!">
</dx:ASPxComboBox>
<dx:ASPxLabel ID="ASPxLabel5" runat="server" Font-Size="12pt" style="z-index: 1; left: 18px; top: 400px; position: absolute" Text="Mahallenizi Seçiniz:" Theme="Youthful" ForeColor="White">
</dx:ASPxLabel>
<dx:ASPxButton ID="BtnMasterPageDevamEt" runat="server" Font-Size="12pt" style="z-index: 1; left: 18px; top: 555px; position: absolute" Text="Devam Et" Theme="PlasticBlue" OnClick="btnClickEski01">
</dx:ASPxButton>
</asp:ContentPlaceHolder>
</div>
<br />
</td>
<td class="auto-style2">
<div style="z-index: 1; left: 257px; top: 144px; position: absolute; height: 784px; width: 862px;background-color:#9ACD32">
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
<p>
<br />
</p>
<p>
</p>
<p>
</p>
<p>
<dx:ASPxBinaryImage ID="ASPxBinaryImage1" runat="server" style="z-index: 1; left: -237px; top: 443px; position: absolute; height: 109px; width: 155px">
</dx:ASPxBinaryImage>
</p>
<p>
</p>
<p>
</p>
<p>
</p>
<p>
</p>
<p>
</p>
<p>
</p>
<p>
</p>
<p>
</p>
<p>
</p>
<p>
</p>
<p style="margin-left: 0px">
</p>
<asp:Label ID="lblDescription" runat="server" ForeColor="White" Font-Names="Comic Sans MS" style="z-index: 1; left: -226px; top: 583px; position: absolute; height: 14px" Text="Açıklama">
</asp:Label>
<p>
</p>
<p>
</p>
<p>
</p>
</asp:ContentPlaceHolder>
</div>
</td>
</tr>
</table>
</div>
</form>
</body>
</html>
DropDownLists aren't null, but my label is. DropDownLists不为null，但我的标签为null。 Why it happens? 为什么会发生？
1 个解决方案
解决方案1
2 2015-04-26 10:23:53
Looking at your code sample. 查看您的代码示例。 You are in stage 'Postback event handling'. 您正处于“回发事件处理”阶段。 In that stage all controls should be ready to use. 在那个阶段，所有控件应准备就绪。
Question is what might cause this unexpected behavior and how to find out issue? 问题是什么可能导致这种意外行为以及如何找出问题？ Here is MasterPage run-time behavior: 这是MasterPage运行时行为：
- Users request a page by typing the URL of the content page(.aspx page) 用户通过键入内容页面（.aspx页面）的URL请求页面
- When the page is fetched, the @ Page directive is read. 提取页面后，将读取@ Page指令。 If the directive references a master page, the master page is read as well. 如果指令引用了母版页，则也会读取母版页。 If this is the first time the pages have been requested, both pages are compiled. 如果这是第一次请求页面，则将同时编译两个页面。
- The master page with the updated content is merged into the control tree of the content page. 具有更新内容的母版页将合并到内容页的控制树中。
- The content of individual Content controls is merged into the corresponding ContentPlaceHolder control in the master page - in other words Content control from .aspx page replacing placeholder content from MasterPage. 单个Content控件的内容将合并到母版页中相应的ContentPlaceHolder控件中-换句话说，.aspx页中的Content控件将替换MasterPage中的占位符内容。
- The resulting merged page is rendered to the browser. 生成的合并页面将呈现给浏览器。
Question is what went wrong in that flow. 问题是该流程出了什么问题。 Why the control in MasterPage was set to null? 为什么将MasterPage中的控件设置为null？ *You have added code inside placeholder on MasterPage which will be replace with Content control and can end up with null values. *您已在MasterPage上的占位符内添加了代码，这些代码将被Content控件替换，并可能以空值结尾。
Hope it will help you. 希望对您有帮助。
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