internal (C# Reference)

不念不忘少年蓝@ 2021-12-12 00:45 218阅读 0赞

The **internal** keyword is an access modifier for types and type members. Internal types or members are accessible only within files in the same assembly, as in this example:

public  class  BaseClass  
\{  
 //  Only accessible within the same assembly   
  internal  static  int  x  =  0 ;  
\}

For a comparison of **internal** with the other access modifiers, see [Accessibility Levels][] and [Access Modifiers (C\# Programming Guide)][Access Modifiers _C_ Programming Guide].

For more information on assemblies, see [Assemblies and the Global Assembly Cache (C\# Programming Guide)][Assemblies and the Global Assembly Cache _C_ Programming Guide].

A common use of internal access is in component-based development because it enables a group of components to cooperate in a private manner without being exposed to the rest of the application code. For example, a framework for building graphical user interfaces could provide Control and Form classes that cooperate using members with internal access. Since these members are internal, they are not exposed to code that is using the framework.

It is an error to reference a type or a member with internal access outside the assembly within which it was defined.

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   <th align="left"><img alt="Note" src="http://i.msdn.microsoft.com/Hash/030c41d9079671d09a62d8e2c1db6973.gif">Note </th> 
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   <td> <p>An <strong>internal</strong> <strong>virtual</strong> method can be overridden in some languages, such as textual Microsoft intermediate language (MSIL) using Ilasm.exe, even though it cannot be overridden using C#.</p> </td> 
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Example

--------------------

This example contains two files, Assembly1.cs and Assembly2.cs. The first file contains an internal base class, BaseClass. In the second file, an attempt to instantiate BaseClass will produce an error.

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][] 代码

Copy  
  
 //  Assembly1.cs  
 //  compile with: /target:library   
 internal  class  BaseClass  
\{  
 public  static  int  intM  =  0 ;  
\}  
  
Copy  
  
 //  Assembly1\_a.cs  
 //  compile with: /reference:Assembly1.dll   
 class  TestAccess  
\{  
 static  void  Main()  
\{  
BaseClass myBase  =  new  BaseClass();  //  CS0122   
  \}  
\}

In this example, use the same files you used in example 1, and change the accessibility level of BaseClass to **public**. Also change the accessibility level of the member IntM to **internal**. In this case, you can instantiate the class, but you cannot access the internal member.

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][] 代码

//  Assembly2.cs  
 //  compile with: /target:library   
 public  class  BaseClass  
\{  
 internal  static  int  intM  =  0 ;  
\}  
  
Copy  
  
 //  Assembly2\_a.cs  
 //  compile with: /reference:Assembly1.dll   
 public  class  TestAccess  
\{  
 static  void  Main()  
\{  
BaseClass myBase  =  new  BaseClass();  //  Ok.   
  BaseClass.intM  =  444 ;  //  CS0117   
  \}  
\}

Reference: http://msdn.microsoft.com/en-us/library/7c5ka91b%28VS.80%29.aspx

转载于:https://www.cnblogs.com/sandy\_liao/archive/2010/11/29/1891490.html

[Accessibility Levels]: http://msdn.microsoft.com/en-us/library/ba0a1yw2%28v=VS.80%29.aspx
[Access Modifiers _C_ Programming Guide]: http://msdn.microsoft.com/en-us/library/ms173121%28v=VS.80%29.aspx
[Assemblies and the Global Assembly Cache _C_ Programming Guide]: http://msdn.microsoft.com/en-us/library/ms173099%28v=VS.80%29.aspx
[ContractedBlock.gif]: https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif
[ExpandedBlockStart.gif]: /images/20211211/9fb8a51620744ee783547199132c2f88.png