Encountered a strange problem today, their practice two hours did not make things right. To Stack Overflow made a post questions, by the way also posted to the blog in question, to see if someone please help. If the issue is resolved, I will issue the reasons for and solutions to put here.
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 is a really good programming sites, popularity, high level. After 5 minutes he has found the answer.
The following is the answer ( the original address 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
{ ... }
