C#-在div ID上使用FindControl时出错 [英] c# - error using FindControl on div id

问题描述

我有一个ASP.NET网站，我试图通过文件后面的C#代码中的div元素访问其div元素.本质上，我想查看div元素是否存在，如果存在，请更改其属性.

I have an ASP.NET site that I am trying to access div elements by their ID from the C# code behind file. Essentially I want to see if a div element exists, and if so, alter its properties.

我发现那里有很多资源，这些资源指向许多不同的解决方案，但似乎没有一个起作用.

I've found many resources out there that point to a dozen different solutions and none of them seem to work.

ASP.Net页面上的HTML:

<div class="contentArea">
     <div class="block" id="button1" runat="server">
            Some Content Here
     </div>
     <div class="block" id="button2" runat="server">
            Some Content Here
     </div>
     <div class="block" id="button3" runat="server">
            Some Content Here
     </div>
</div>

C#后面的代码(我尝试过的示例):

System.Web.UI.HtmlControls.HtmlGenericControl div1 = (System.Web.UI.HtmlControls.HtmlGenericControl)this.FindControl("button1");
div1.Attributes["class"] = "classNameHere";

或

Control div1 = this.FindControl("button1");
div1.GetType();

当代码到达上述每个示例的第二行时，我得到一个错误:

When the code gets to the second line of each of the above examples, I get an error:

对象引用未设置为对象的实例.

Object reference not set to an instance of an object.

如果我尝试以下操作:

if (div1 != null)
{
    // Do Something;
}

什么都没有发生，因为div1始终设置为null.具有讽刺意味的是，如果我查看Locals窗口并进行检查，则可以在清单中看到button#ID，因此我知道它们在那里，但是系统的行为就像找不到控件一样.

Nothing ever happens because div1 is always set to null. Ironically, if I look at the Locals window and examine this, I can see the button# ids in the listing, so I know they are there, but the system is acting like it isn't finding the control.

我的最终目标是找到按钮div的最大ID号(在我的html示例中，最大ID将为3(button3).也许有更好的方法可以解决此问题，但是无论哪种方式，一次我有自己的最大ID，我希望能够触摸每个div并更改一些CSS属性.

My ultimate goal is to find the max id # of the button divs (looking at my html example, the max id would be 3 (button3). Maybe there is a better way to go about it, but either way, once I have my max id, I want to be able to touch each div and alter some css properties.

尽管我可以通过jQuery轻松完成所有这些操作，但在这种情况下，我需要在C#中执行此操作.

Although I could easily do all of this via jQuery, in this instance I need to do this in C#.

我们非常感谢您的帮助.如果您需要更多信息，请告诉我.

Any help is much appreciated. If you need more info, let me know.

更新我从头开始创建了一个新的C#Web项目.在添加母版页(并且不对其进行更改)并使用母版页添加Web表单之后，我仅在Content ID ="Content2"下的Web表单中添加了一行:

UPDATE I created a new C# web project from scratch. After adding a masterpage (and not altering it) and adding a webform using masterpage, I only added one line to the webform under Content ID="Content2":

<div id="button1"></div>

从后面的C#代码开始，我仍然遇到与以前完全相同的问题.

From c# code behind I still run into the same exact issue as before.

最终更新和答案我感到震惊的是，没有人(包括我自己)从上述更新中发现我的错误.当我在div下从头开始创建新项目时，我从未放过runat ="server".这是我从头开始解决新项目下的问题的方法:

FINAL UPDATE AND ANSWER I'm shocked no one (including myself) caught my mistake from the above update. I never put runat="server" when I created a new project from scratch under the div. Here is how I fixed my problem under my new project from scratch:

将runat ="server"添加到div:

Add runat="server" to div:

<div id="button1" runat="server"></div>

然后我在MasterPage下的ContentPlaceHolder上执行了FindControl:

Then I did a FindControl on the ContentPlaceHolder under the MasterPage:

ContentPlaceHolder myPlaceHolder = (ContentPlaceHolder)Master.FindControl("ContentPlaceHolder1");

注意:这是默认创建的Site.Master页面上ContentPlaceHolder代码的样子:

Note: This is what the ContentPlaceHolder code looks like on the Site.Master page created by default:

<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">

</asp:ContentPlaceHolder>

在后面的代码中找到此ContentPlaceHolder之后，我在此占位符中搜索button1:

After finding this ContentPlaceHolder in code behind, I then searched within this placeholder for button1:

using System.Web.UI.HtmlControls;
HtmlControl myControl = (HtmlControl)myPlaceHolder.FindControl("button1");

最后，我检查myControl是否为空:

Finally I check to see if myControl is null:

if (myControl != null)
{
    \\ Do Something
}

当我运行这段代码时，它找到了我正在寻找的div.这是所有内容汇总在一起的完整代码:

When I ran this code, it found the div I was looking for. Here is the complete code behind all put together:

using System.Web.UI.HtmlControls;

ContentPlaceHolder myPlaceHolder = (ContentPlaceHolder)Master.FindControl("ContentPlaceHolder1");
HtmlControl myControl = (HtmlControl)myPlaceHolder.FindControl("button1");

if (myControl != null)
{
    // Do Something
}

推荐答案

如果您的页面使用的是MasterPage，则div控件将不在控件的主要集合中.该集合仅包含指向您的MasterPage的ContentPlaceholder的Content控件.

If your page is using a MasterPage, the div control will not be in the main collection of controls. That collection only contains the Content controls pointing to the ContentPlaceholder of your MasterPage.

共有三个选项:

1. 在Content控件上使用 FindControl : contentControl.FindControl("button1");
2. 执行递归 FindControl ，直到找到所需的控件
3. 通常，将div控件的声明添加到designer.cs代码的后面，因此您可以直接通过其名称访问该控件: button1.Attributes ["class"] ="classNameHere";

1. Use FindControl on the Content control: contentControl.FindControl("button1");
2. Do a recursive FindControl until you find the control you need
3. Normally, a declaration of your div control is added to your designer.cs codebehind, so you can directly access the control by its name: button1.Attributes["class"] = "classNameHere";

更新

我创建了一个母版页，向其中添加了内容页，并向内容页添加了< div id ="button1" runat ="server">某些文本</div>

在内容页面的代码中，添加了以下代码:

In the codebehind of my Content Page, I added this code:

protected void Page_Load(object sender, EventArgs e)
{
    var control = FindHtmlControlByIdInControl(this, "button1");

    if (control != null)
    {
        control.Attributes["class"] = "someCssClass";
    }
}

private HtmlControl FindHtmlControlByIdInControl(Control control, string id)
{
    foreach (Control childControl in control.Controls)
    {
        if (childControl.ID != null && childControl.ID.Equals(id, StringComparison.OrdinalIgnoreCase) && childControl is HtmlControl)
        {
            return (HtmlControl)childControl;
        }

        if (childControl.HasControls())
        {
            HtmlControl result = FindHtmlControlByIdInControl(childControl, id);
            if (result != null) return result;
        }
    }

    return null;
}

这对我有用.

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