Home Library Learn Downloads Support Community
Sign in | United States - English | |
1 out of 2 rated this helpful - Rate this topic

COMException Class

.NET Framework 4

The exception that is thrown when an unrecognized HRESULT is returned from a COM method call.

System.Object
  System.Exception
    System.SystemException
      System.Runtime.InteropServices.ExternalException
        System.Runtime.InteropServices.COMException
          System.DirectoryServices.DirectoryServicesCOMException

Namespace:  System.Runtime.InteropServices
Assembly:  mscorlib (in mscorlib.dll)
C#
C++
F#
VB
Copy 
[SerializableAttribute]
[ComVisibleAttribute(true)]
public class COMException : ExternalException

The COMException type exposes the following members.

  Name Description
Public method COMException() Initializes a new instance of the COMException class with default values.
Public method COMException(String) Initializes a new instance of the COMException class with a specified message.
Protected method COMException(SerializationInfo, StreamingContext) Initializes a new instance of the COMException class from serialization data.
Public method COMException(String, Exception) Initializes a new instance of the COMException class with a specified error message and a reference to the inner exception that is the cause of this exception.
Public method COMException(String, Int32) Initializes a new instance of the COMException class with a specified message and error code.
Top
  Name Description
Public property Data Gets a collection of key/value pairs that provide additional user-defined information about the exception. (Inherited from Exception.)
Public property ErrorCode Gets the HRESULT of the error. (Inherited from ExternalException.)
Public property HelpLink Gets or sets a link to the help file associated with this exception. (Inherited from Exception.)
Protected property HResult Gets or sets HRESULT, a coded numerical value that is assigned to a specific exception. (Inherited from Exception.)
Public property InnerException Gets the Exception instance that caused the current exception. (Inherited from Exception.)
Public property Message Gets a message that describes the current exception. (Inherited from Exception.)
Public property Source Gets or sets the name of the application or the object that causes the error. (Inherited from Exception.)
Public property StackTrace Gets a string representation of the immediate frames on the call stack. (Inherited from Exception.)
Public property TargetSite Gets the method that throws the current exception. (Inherited from Exception.)
Top
  Name Description
Public method Equals(Object) Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected method Finalize Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public method GetBaseException When overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions. (Inherited from Exception.)
Public method GetHashCode Serves as a hash function for a particular type. (Inherited from Object.)
Public method GetObjectData When overridden in a derived class, sets the SerializationInfo with information about the exception. (Inherited from Exception.)
Public method GetType Gets the runtime type of the current instance. (Inherited from Exception.)
Protected method MemberwiseClone Creates a shallow copy of the current Object. (Inherited from Object.)
Public method ToString Converts the contents of the exception to a string. (Overrides ExternalException.ToString().)
Top
  Name Description
Protected event SerializeObjectState Occurs when an exception is serialized to create an exception state object that contains serialized data about the exception. (Inherited from Exception.)
Top

The common language runtime transforms well-known HRESULTs to.NET exceptions, enabling COM objects to return meaningful error information to managed clients. The HRESULT to exception mapping also works in the other direction by returning specific HRESULTs to unmanaged clients. For mapping details, see How to: Map HRESULTs and Exceptions.

When the runtime encounters an unfamiliar HRESULT (an HRESULT that lacks a specific, corresponding exception), it throws an instance of the COMException class. This all-purpose exception exposes the same members as any exception, and includes a public ErrorCode property that contains the HRESULT returned by the callee. If an error message is available to the runtime (obtained from the IErrorInfo interface or the Err object in Visual Basic, or in some cases from the operating system), the message is returned to the caller. However, if the COM component developer fails to include an error message, the runtime returns the eight-digit HRESULT in place of a message string. Having an HRESULT allows the caller to determine the cause of the generic exception.

Although you can use the COMException class to return specific HRESULTs to unmanaged clients, throwing a specific.NET exception is better than using a generic exception. Consider that managed clients as well as unmanaged clients can use your.NET object, and throwing an HRESULT to a managed caller is less comprehendible than throwing an exception.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
Did you find this helpful?
(1500 characters remaining)
Community Content Add
Annotations FAQ