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从内容页查找控件（母版页内部），错误 = NullReferenceException

发布于 2024-12-16 12:45:56 字数 5443 浏览 2 评论 0原文

请参阅下面的简单示例以了解我的情况。
（注意代码内的注释）

母版页（ASPX）：

<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Site1.master.cs" Inherits="NiceFileExplorer.Site1" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <asp:ContentPlaceHolder ID="head" runat="server">
    </asp:ContentPlaceHolder>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <span runat="server" id="SummaryContainer">
            <asp:Label ID="lblDownload_Count_By_UserID_Today_Title" runat="server" Text="Count :"
                ToolTip="Your Download Count-Today" CssClass="lblTitleInStatistics_Master"></asp:Label>
            <asp:Label ID="lblDownload_Count_By_UserID_Today" runat="server" Text="<%# Download_Count_By_UserID_Today() %>"
                CssClass="lblCountInStatistics_Master" ToolTip="Your Download Count-Today"></asp:Label>
            <span style="color: white;">&nbsp;|&nbsp;</span>
            <asp:Label ID="lblDownload_Size_By_UserID_Today_Title" runat="server" Text="Size :"
                ToolTip="Your Download Size-Today" CssClass="lblTitleInStatistics_Master"></asp:Label>
            <asp:Label ID="lblDownload_Size_By_UserID_Today" runat="server" Text="<%# Download_Size_By_UserID_Today() %>"
                CssClass="lblCountInStatistics_Master" ToolTip="Your Download Size-Today"></asp:Label>
        </span>
    </div>
    <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server" ViewStateMode="Inherit" ClientIDMode="Static">
    </asp:ContentPlaceHolder>
    </div>
    </form>
</body>
</html>

如您所见，我设置了 ClientIDMode="Static"。

母版页（代码隐藏）：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace NiceFileExplorer
{
    public partial class Site1 : System.Web.UI.MasterPage
    {
        protected void Page_Load(object sender, EventArgs e)
        {
             SummaryContainer.DataBind();
        }

        protected string Download_Count_By_UserID_Today()
        {
            //Read New Count From DataBase
            //return Count;
            return "Test";
        }

        protected string Download_Size_By_UserID_Today()
        {
            //Read New Size From DataBase
            //return Size;
            return "Test";
        }
    }
}

内容页（ASPX）：

<%@ Page Title="" Language="C#" MasterPageFile="~/Site1.Master" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="NiceFileExplorer.WebForm1" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
Conntent Page
</asp:Content>

内容页（代码隐藏）：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace NiceFileExplorer
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            MyMethod();
        }

        private void MyMethod()
        {
            //Add New Downloaded File Info To DataBase(); -> For Getting Count And Size Of Them Per Day

            //Here I Wand To Access Master Page Controls And Update Count And Size Lables
            //So, I Tried Codes Below Without Any Results -> How Can I Fix This ?
            var SummaryContainer = (System.Web.UI.HtmlControls.HtmlGenericControl)Page.Master.FindControl("SummaryContainer");
            SummaryContainer.DataBind();
            SummaryContainer.InnerHtml = "<h2>Hello World</h2>";

            //After Update Those Lables Failed, I test the codes Below With Null Execption Error -> How Can I Fix This ?
            var lblDownload_Count_By_UserID_Today_Title = (Label)Page.Master.FindControl("lblDownload_Count_By_UserID_Today_Title");
            lblDownload_Count_By_UserID_Today_Title.Text = "test";

            DwonloadFile();
        }

        private void DwonloadFile()
        {
            //A Class (Method) That Shows Download Window To My Users, So Page_Load Of Master Will Never Fire...
            //And This Is The Reason That I want to update count & size lables from content page
        }

    }
}

我想从内容页的代码隐藏中数据绑定摘要容器（跨度）。 所以我尝试了下面的代码：

            var SummaryContainer = (System.Web.UI.HtmlControls.HtmlGenericControl)Page.Master.FindControl("SummaryContainer");
            SummaryContainer.DataBind():

但我看不到新的结果。
失败之后，我尝试从内容页代码后面查找标签的文本（该标签位于 Master 内部）进行测试，如下所示：var

lblDownload_Count_By_UserID_Today_Title = (Label)Page.Master.FindControl("lblDownload_Count_By_UserID_Today_Title");
                    lblDownload_Count_By_UserID_Today_Title.Text = "test";

但我有 System.NullReferenceException 错误：

未设置对象引用对象的实例。

我如何修复该错误并强制该跨度向我显示新结果？

提前致谢

原文

Please See The Simple Example Below For Understanding My situation.
(Attention To Comments Inside Codes)

Master Page (ASPX) :

<%@ Master Language="C#" AutoEventWireup="true" CodeBehind="Site1.master.cs" Inherits="NiceFileExplorer.Site1" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <asp:ContentPlaceHolder ID="head" runat="server">
    </asp:ContentPlaceHolder>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <span runat="server" id="SummaryContainer">
            <asp:Label ID="lblDownload_Count_By_UserID_Today_Title" runat="server" Text="Count :"
                ToolTip="Your Download Count-Today" CssClass="lblTitleInStatistics_Master"></asp:Label>
            <asp:Label ID="lblDownload_Count_By_UserID_Today" runat="server" Text="<%# Download_Count_By_UserID_Today() %>"
                CssClass="lblCountInStatistics_Master" ToolTip="Your Download Count-Today"></asp:Label>
            <span style="color: white;"> | </span>
            <asp:Label ID="lblDownload_Size_By_UserID_Today_Title" runat="server" Text="Size :"
                ToolTip="Your Download Size-Today" CssClass="lblTitleInStatistics_Master"></asp:Label>
            <asp:Label ID="lblDownload_Size_By_UserID_Today" runat="server" Text="<%# Download_Size_By_UserID_Today() %>"
                CssClass="lblCountInStatistics_Master" ToolTip="Your Download Size-Today"></asp:Label>
        </span>
    </div>
    <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server" ViewStateMode="Inherit" ClientIDMode="Static">
    </asp:ContentPlaceHolder>
    </div>
    </form>
</body>
</html>

as you see i set ClientIDMode="Static".

Master Page (CodeBehind) :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace NiceFileExplorer
{
    public partial class Site1 : System.Web.UI.MasterPage
    {
        protected void Page_Load(object sender, EventArgs e)
        {
             SummaryContainer.DataBind();
        }

        protected string Download_Count_By_UserID_Today()
        {
            //Read New Count From DataBase
            //return Count;
            return "Test";
        }

        protected string Download_Size_By_UserID_Today()
        {
            //Read New Size From DataBase
            //return Size;
            return "Test";
        }
    }
}

Content Page (ASPX) :

<%@ Page Title="" Language="C#" MasterPageFile="~/Site1.Master" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="NiceFileExplorer.WebForm1" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
Conntent Page
</asp:Content>

Content Page (CodeBehind) :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace NiceFileExplorer
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            MyMethod();
        }

        private void MyMethod()
        {
            //Add New Downloaded File Info To DataBase(); -> For Getting Count And Size Of Them Per Day

            //Here I Wand To Access Master Page Controls And Update Count And Size Lables
            //So, I Tried Codes Below Without Any Results -> How Can I Fix This ?
            var SummaryContainer = (System.Web.UI.HtmlControls.HtmlGenericControl)Page.Master.FindControl("SummaryContainer");
            SummaryContainer.DataBind();
            SummaryContainer.InnerHtml = "<h2>Hello World</h2>";

            //After Update Those Lables Failed, I test the codes Below With Null Execption Error -> How Can I Fix This ?
            var lblDownload_Count_By_UserID_Today_Title = (Label)Page.Master.FindControl("lblDownload_Count_By_UserID_Today_Title");
            lblDownload_Count_By_UserID_Today_Title.Text = "test";

            DwonloadFile();
        }

        private void DwonloadFile()
        {
            //A Class (Method) That Shows Download Window To My Users, So Page_Load Of Master Will Never Fire...
            //And This Is The Reason That I want to update count & size lables from content page
        }

    }
}

i want to DataBind SummaryContainer(a span) from content page's code-behind.
so i tried the codes below :

            var SummaryContainer = (System.Web.UI.HtmlControls.HtmlGenericControl)Page.Master.FindControl("SummaryContainer");
            SummaryContainer.DataBind():

but i can not see new results.
After That Fail I tried to find a label's text(that label is inside Master) from content page code behind for test like below : var

lblDownload_Count_By_UserID_Today_Title = (Label)Page.Master.FindControl("lblDownload_Count_By_UserID_Today_Title");
                    lblDownload_Count_By_UserID_Today_Title.Text = "test";

but i have System.NullReferenceException ERROR :

Object reference not set to an instance of an object.

how can i fix that error and force that span to show me new results?

thanks in advance

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评论（1）

谁对谁错谁最难过 2024-12-23 12:45:56

在一个项目中，我在母版页上使用了一个界面：

((IMasterPage)Page.Master).MyProperty = "test";

但就您而言，就我个人而言，我不会将所有内容都放在母版页上，而是将您的 SummaryContainer 放入 UserControl 中，并有另一个 内容占位符。
然后 Page_Load 方法将能够访问属性，并且在以后的页面上，您可以通过使用不同的 UserControl 填充第一个 PlaceHolder 来获得不同的摘要信息。

还调试愚蠢的错误，是在 .Master.FindControl 还是在 lbl.Text 抛出 Null 异常？

我现在无法自己调试它，但这是否是由于 页面生命周期，即内容页面加载先于母版页面加载？

In a project I used an interface on the masterpage:

((IMasterPage)Page.Master).MyProperty = "test";

But in your case, personally instead of putting all that on the master page, I'd put your SummaryContainer into a UserControl, and have another ContentPlaceHolder.
Then the Page_Load method will be able to access the properties, and on future pages you could have different summary info by filling that first PlaceHolder with a different UserControl.

Also debugging stupid errors, is the Null exception being thrown at .Master.FindControl or at lbl.Text?

I'm unable to debug it for myself right now, but would it be due to the page life cycle, namely that Content Page Load comes before Master Page Load?

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