1 out of 3 rated this helpful - Rate this topic

COMException Class

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

Namespace:  System.Runtime.InteropServices
Assembly:  mscorlib (in mscorlib.dll)
[SerializableAttribute]
[ComVisibleAttribute(true)]
public class COMException : ExternalException

The COMException type exposes the following members.

  NameDescription
Public methodCOMException()Initializes a new instance of the COMException class with default values.
Public methodCOMException(String)Initializes a new instance of the COMException class with a specified message.
Protected methodCOMException(SerializationInfo, StreamingContext)Initializes a new instance of the COMException class from serialization data.
Public methodCOMException(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 methodCOMException(String, Int32)Initializes a new instance of the COMException class with a specified message and error code.
Top
  NameDescription
Public propertyDataGets a collection of key/value pairs that provide additional user-defined information about the exception. (Inherited from Exception.)
Public propertyErrorCodeGets the HRESULT of the error. (Inherited from ExternalException.)
Public propertyHelpLinkGets or sets a link to the help file associated with this exception. (Inherited from Exception.)
Protected propertyHResultGets or sets HRESULT, a coded numerical value that is assigned to a specific exception. (Inherited from Exception.)
Public propertyInnerExceptionGets the Exception instance that caused the current exception. (Inherited from Exception.)
Public propertyMessageGets a message that describes the current exception. (Inherited from Exception.)
Public propertySourceGets or sets the name of the application or the object that causes the error. (Inherited from Exception.)
Public propertyStackTraceGets a string representation of the immediate frames on the call stack. (Inherited from Exception.)
Public propertyTargetSiteGets the method that throws the current exception. (Inherited from Exception.)
Top
  NameDescription
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetBaseExceptionWhen overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions. (Inherited from Exception.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetObjectDataWhen overridden in a derived class, sets the SerializationInfo with information about the exception. (Inherited from Exception.)
Public methodGetTypeGets the runtime type of the current instance. (Inherited from Exception.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringConverts the contents of the exception to a string. (Overrides ExternalException.ToString().)
Top
  NameDescription
Protected eventSerializeObjectStateOccurs 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)
Thank you for your feedback

Community Additions

ADD
Show:
© 2014 Microsoft. All rights reserved.