usercontrol中的所有控件均为空 [英] All controls are null within usercontrol

问题描述

我有一个使用其他控件的UserControl的UserControl.

I have a UserControl which uses a UserControl, among other controls.

在 ascx 文件中，我具有以下代码:

In the ascx file I have the following code:

<%@ Register TagPrefix="tag" Namespace="some.name.space" Assembly="some.assembly" %>
<tag:control ID="test" runat="server" />

在我的 Page_Load 方法中，我尝试像这样设置测试的属性:

In my Page_Load method, I try to set a property on test like so:

test.Text = "Hello World!";

这实际上在我的用户控件 test 中设置了文字控件的Text属性.

This actually sets the Text property of a literal control in my user control test.

这将引发异常:

对象引用未设置为对象的实例

Object reference not set to an instance of an object

尝试设置

lblTest.Text = value; 

为空的对象是 lblTest .

我没有正确添加用户控件吗?注册代码时，我应该-还是必须-指定 Src 属性?如果是这样，我必须注册我使用的每个用户控件吗?

Am I not adding the user control correctly? Should I - or do I have to - specify the Src property when registering a Tag? If so, I'd have to register every usercontrol I use?

这也将导致没有任何控件加载到usercontrol中，并且usercontrol中的所有控件均为空.

This also results in no controls loading in usercontrol and all controls are null within usercontrol.

推荐答案

如果用户控件在当前项目中，则需要在注册语句中包含src:

If the user control is in your current project, then you need to include the src in the register statement:

<%@ Register TagPrefix="uc1" TagName="NavTop" Src="controls/NavTop.ascx" %>

但是，如果您在多个页面中使用此用户控件，则也可以在web.config中注册它:

However, if you use this user control in more than one page, then you can also register it in web.config:

<system.web>
  <pages>
    <controls>
      <add tagPrefix="uc1" tagName="NavTop" src="~/controls/NavTop.ascx" />
    </controls>
  </pages>
</system.web>

要注意的另一件事:在某些情况下，如果仅在源代码视图中进行更改，Visual Studio设计器就不会在页面上看到"对控件的更改.例如，如果更改控件名称，则最终可能会在ascx中使用新名称的控件，而在设计器文件中使用旧名称的控件的引用.在运行时，这将导致设计器文件属性为null.

One other thing to be aware of: there are times when the visual studio designer does not "see" your changes to controls on the page if you only make the changes in source view. If you change a control name, for example, you could end up with a control with the new name in the ascx but a reference to a control with the old name in the designer file. At runtime, this will result in the designer file property being null.

经过多次刻录后，如果我在源视图中进行了任何更改，我将检查以查看设计器文件是否已正确更新，或者我切换到设计视图，进行较小的更改，然后保存页面/用户控件.

After having been burnt by this a number of times, if I make any changes in source view, I either check to see that the designer file has been updated correctly or I switch to design view, make a minor change, then save the page/user control.

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