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ComVisibleAttribute Class

Controls accessibility of an individual managed type or member, or of all types within an assembly, to COM.

Namespace: System.Runtime.InteropServices
Assembly: mscorlib (in mscorlib.dll)

[AttributeUsageAttribute(AttributeTargets.Assembly|AttributeTargets.Class|AttributeTargets.Struct|AttributeTargets.Enum|AttributeTargets.Method|AttributeTargets.Property|AttributeTargets.Field|AttributeTargets.Interface|AttributeTargets.Delegate, Inherited=false)] 
[ComVisibleAttribute(true)] 
public sealed class ComVisibleAttribute : Attribute
/** @attribute AttributeUsageAttribute(AttributeTargets.Assembly|AttributeTargets.Class|AttributeTargets.Struct|AttributeTargets.Enum|AttributeTargets.Method|AttributeTargets.Property|AttributeTargets.Field|AttributeTargets.Interface|AttributeTargets.Delegate, Inherited=false) */ 
/** @attribute ComVisibleAttribute(true) */ 
public final class ComVisibleAttribute extends Attribute
AttributeUsageAttribute(AttributeTargets.Assembly|AttributeTargets.Class|AttributeTargets.Struct|AttributeTargets.Enum|AttributeTargets.Method|AttributeTargets.Property|AttributeTargets.Field|AttributeTargets.Interface|AttributeTargets.Delegate, Inherited=false) 
ComVisibleAttribute(true) 
public final class ComVisibleAttribute extends Attribute

You can apply this attribute to assemblies, interfaces, classes, structures, delegates, enumerations, fields, methods, or properties.

The default is true, which indicates that the managed type is visible to COM. This attribute is not needed to make public managed assemblies and types visible; they are visible to COM by default. Only public types can be made visible. The attribute cannot be used to make an otherwise internal or protected type visible to COM or to make members of a nonvisible type visible.

Setting the attribute to false on the assembly hides all public types within the assembly. You can selectively make types within the assembly visible by setting the individual types to true. Setting the attribute to false on a specific type hides that type and its members. However, you cannot make members of a type visible if the type is invisible. Setting the attribute to false on a type prevents that type from being exported to a type library; classes are not registered; interfaces are never responsive to unmanaged QueryInterface calls.

Unless you explicitly set a class and its members to false, inherited classes can expose to COM base class members that are invisible in the original class. For example, if you set ClassA to false and do not apply the attribute to its members, the class and its members are invisible to COM. However, if you derive ClassB from ClassA and export ClassB to COM, ClassA members become visible base class members of ClassB.

For a detailed description of the export process, see Assembly to Type Library Conversion Summary.

The following example shows how you can control the visibility to COM of a class so that its members are invisible. By setting ComVisibleAttribute to false on MyClass, and false on MyMethod and MyProperty, you can avoid inadvertently exposing the members to COM through inheritance.

using System.Runtime.InteropServices;

[ComVisible(false)]
class MyClass
{
   public MyClass()
   {
      //Insert code here.
   }
   
   [ComVisible(false)]
   public int MyMethod(string param) 
   {
      return 0;
   }

   public bool MyOtherMethod() 
   {
      return true;
   }

   [ComVisible(false)]
   public int MyProperty
   {
      get
      {
         return MyProperty;
      }
   }
}

import System.Runtime.InteropServices.*;

/** @attribute ComVisible(false)
 */
class MyClass
{
    public MyClass()
    {
        //Insert code here.
    } //MyClass
   
    /** @attribute ComVisible(false)
     */
    public int MyMethod(String param)
    {
        return 0;
    } //MyMethod

    public boolean MyOtherMethod()
    {
        return true;
    } //MyOtherMethod

    /** @attribute ComVisible(false)
     */
    /** @property 
     */
    public int get_MyProperty()
    {
        return get_MyProperty();
    }//get_MyProperty
} //MyClass

import System.Runtime.InteropServices;

ComVisible(false) class MyClass
{
   public function MyClass()
   {
      //Insert code here.
   }
   
   ComVisible(false) public function MyMethod(param : String) : int 
   {
      return 0;
   }

   public function MyOtherMethod() : boolean
   {
      return true;
   }

   ComVisible(false) public function get MyProperty() : int 
   {
	   return MyProperty;
   }
}

System.Object
   System.Attribute
    System.Runtime.InteropServices.ComVisibleAttribute

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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