泛型窗体继承时不能在设计器中显示，为神马？

今天遇到一奇怪的问题，自己搞了2个小时没有弄好。到Stack Overflow发了个帖子提问，顺便把问题也贴到博客里，如有人看到请帮忙。如果问题解决了，我会把问题的原因和解决方案放到这里来。

I meet a problem today. As following.
I create a generic Form , 
public class Form1<T>:Form
Then I create another inheritance form, 
public class From2:Form1<string>.
The form2 cannot be shown in the VS designer, the error message is  "all the classes in the file cannot be designed", (this error message is translated from Chinese, the Chinese message is 文件中的类都不能进行设计).
But this program can be compiled successfully, and when it runs, both Form1 and From2 can work.

 

Anyone can give me some help about this ? Thanks.

I am not a native English speaker, I hope I have described my question clear.

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Stack Overflow果然是个好的编程网站，人气旺，水平高。5分钟后已经找到答案了。

以下为答案（原文地址http://adamhouldsworth.blogspot.com/2010/02/winforms-visual-inheritance-limitations.html）

I have a small personal project going that involves a WinForms GUI.  I have a series of data listing and editing user controls that I decided to refactor.  There were 5 of each, and out of each they used roughly 80%-90% of the same code, just with naming changes.

A fantastic case of "same whitespace, different values".  I read this a long time ago, but for some reason it stuck.

Supporting Generics

My first port of call was a base class for each of the two user controls.  However, I wanted to migrate even logic involving the business class to the base class, which involved knowing about the business class type.

Step in: Generics.

Step in: first problem.

Using generics causes the designer interface in Visual Studio to crash, as it breaks one of the rules about knowing the base class type.  Microsoft explicitly say generics are not supported.  Fair enough.

The workaround for this (as specified in the previous link) is to create a concrete implementation of the generic base class using a dummy intermediary:

- BaseControl<T> : UserControl
- CustomerControl_Design : BaseControl<Customer>
- CustomerControl : CustomerControl_Design

The CustomerControl_Design class will not have any designer support, and you shouldn't actually need it.  But, your CustomerControl class now does - the peasents rejoice.

I've wrapped the code in compiler tags, so that when it doesn't need design-time support, superfluous code is cut:

#if
 DEBUG

namespace
 MyNamespace

{

    using
 System;

    public
 partial
 class
 CustomerEditorControl_Design
 : BaseEditorControl<Customer>

   {

       public
 CustomerEditorControl_Design()      : base
()

        {

            InitializeComponent();

        }

    }

}

#endif

public
 partial
 class
 CustomerEditorControl

#if
 DEBUG  : CustomerEditorControl_Design

#else
  : BaseEditorControl<Customer>

#endif

    { ...  }