我发现回答。

只有控制从 TemplateControl 继承，它实现了作INamingContainer 接口。

和明显＆LT; D​​IV RUNAT服务器＆GT; 是不是其中之一。

即。 用户控件：

 公共类用户控件：TemplateControl，IAttributeAccessor，INonBindingContainer，作INamingContainer，IUserControlDesignerAccessor
{...}
 

即。 的ContentPlaceHolder ：

 公共类的ContentPlaceHolder：控制，INonBindingContainer，作INamingContainer
{...}
 

在这里我可以看到所有这些控件：

I have this structure :

Page
 |
 +---Ascx
      |
      +---<div  runat="server">
                    |
                    +---<asp:button>

I already know that Findcontrol doesn't work recursively .

However when I pressed the button and went to debug and wrote :

this.FindControl("btn1") it did find the "button"

But

• this= the ascx
• There is a div runat server which wraps the button

So how did it find it ? According to the definition , it doesn't suppose to work.

Msdn :

Control.FindControl --> The method does not search throughout a hierarchy of controls within controls

I found the answer.

Only controls which inherits from TemplateControl, which implements the INamingContainer interface.

and obviously <div runat server> is not one of them.

i.e. UserControl :

public class UserControl : TemplateControl, IAttributeAccessor, INonBindingContainer, INamingContainer, IUserControlDesignerAccessor
{...}

i.e. ContentPlaceHolder:

public class ContentPlaceHolder : Control, INonBindingContainer, INamingContainer
{...} 

and here I can see all those controls :