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 methodSupported by Portable Class LibraryCOMException()Initializes a new instance of the COMException class with default values.
Public methodSupported by Portable Class LibraryCOMException(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 methodSupported by Portable Class LibraryCOMException(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 methodSupported by Portable Class LibraryCOMException(String, Int32)Initializes a new instance of the COMException class with a specified message and error code.
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  NameDescription
Public propertySupported by Portable Class LibraryDataGets 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 propertySupported by Portable Class LibraryHelpLinkGets or sets a link to the help file associated with this exception. (Inherited from Exception.)
Public propertySupported by Portable Class LibraryHResultGets or sets HRESULT, a coded numerical value that is assigned to a specific exception. (Inherited from Exception.)
Public propertySupported by Portable Class LibraryInnerExceptionGets the Exception instance that caused the current exception. (Inherited from Exception.)
Public propertySupported by Portable Class LibraryMessageGets a message that describes the current exception. (Inherited from Exception.)
Public propertySupported by Portable Class LibrarySourceGets or sets the name of the application or the object that causes the error. (Inherited from Exception.)
Public propertySupported by Portable Class LibraryStackTraceGets 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.)
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  NameDescription
Public methodSupported by Portable Class LibraryEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodSupported by Portable Class LibraryFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by Portable Class LibraryGetBaseExceptionWhen overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions. (Inherited from Exception.)
Public methodSupported by Portable Class LibraryGetHashCodeServes as the default hash function. (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 methodSupported by Portable Class LibraryMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringConverts the contents of the exception to a string. (Overrides ExternalException.ToString().)
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  NameDescription
Protected eventSerializeObjectStateOccurs when an exception is serialized to create an exception state object that contains serialized data about the exception. (Inherited from Exception.)
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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: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

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