[FxCop.设计规则]1. 抽象类不应该拥有构造函数

1.     抽象类不应该拥有构造函数

原文引用：

http://www.gotdotnet.com/team/fxcop/docs/rules.aspx?version=unstable&url=/Design/AbstractTypesShouldNotHaveConstructors.html
Abstract types should not have constructors

TypeName:	AbstractTypesShouldNotHaveConstructors
CheckId:	CA1012
Category:	Microsoft.Design
Message Level:	CriticalWarning
Certainty:	95%
Breaking Change:	NonBreaking

Cause: A public type is abstract and has a public constructor.

Rule Description

Constructors on abstract types can only be called by derived types. Because public constructors create instances of a type, and you cannot create instances of an abstract type, an abstract type with a public constructor is incorrectly designed.

How to Fix Violations

To fix a violation of this rule, either make the constructor protected, or do not declare the type as abstract.

When to Exclude Messages

Do not exclude a message from this rule.

Example Code

The following example contains an abstract type that violates this rule, and an abstract type that is correctly implemented.

[C#]

using System;
 
namespace DesignLibrary
{
   public abstract class BadAbstractClassWithConstructor
   {
      // Violates rule: AbstractTypesShouldNotHaveConstructors.
      public BadAbstractClassWithConstructor()
      {
      // Add constructor logic here.
      }
   }
 
   public abstract class GoodAbstractClassWithConstructor
   {
      protected GoodAbstractClassWithConstructor()
      {
         // Add constructor logic here.
      }
   }
}

引起的原因：（Cause）

一个公共抽象类型拥有一个公共的构造函数

描述：（Rule Description ）

构造函数被用来建立一个对象实例，但是你不能建立一个抽象类型的实例，抽象类型的构造函数就仅仅能够被它的继承类型使用。因此，为一个抽象类构造公共构造函数是一个错误的设计。

修复：（How to Fix Violations）

如果需要修复这个问题，可以声明这个构造函数为保护型，或者，声明这个类型不是一个抽象类型。