COMException COMException COMException COMException Class
The exception that is thrown when an unrecognized HRESULT is returned from a COM method call.
public ref class COMException : System::Runtime::InteropServices::ExternalException
[System.Runtime.InteropServices.ComVisible(true)] [System.Serializable] public class COMException : System.Runtime.InteropServices.ExternalException
type COMException = class inherit ExternalException
Public Class COMException Inherits ExternalException
The common language runtime transforms well-known HRESULTs to .NET Framework 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 inherits 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.
Handling a COMException exception
The following are some considerations for troubleshooting a COMException exception.
Check the ErrorCode property
When the runtime encounters an unfamiliar HRESULT and throws a COMException exception, the ErrorCode property includes either the error message or, if an error message is unavailable, the eight-digit HRESULT value. The error message or the HRESULT value can help you determine the cause of the exception.
For a list of HRESULT values, see Common HRESULT Values.
Late-bound arguments and Microsoft Office objects
When passing late-bound arguments to methods of Microsoft Office objects, a COMException exception may be thrown when the objects are COM objects. The late binder assumes that such method calls involve a
ByRef parameter and that the property you pass has a
set accessor. If the property does not, the .NET Framework generates a MissingMethodException exception (with a
CORE_E_MISSINGMETHOD HRESULT ). To work around this behavior, use early-bound objects or pass a variable instead of a property of the object.
Visual Studio and the hosting process
COM is used to communicate between Visual Studio and the hosting process. Because it is used before code runs, a call to CoInitializeSecurity causes this exception to be thrown.
In some cases, running Visual Studio as Administrator may resolve the issue. You can also disable the hosting process.
Throwing a COMException exception
Although you can use the COMException class to return specific HRESULTs to unmanaged clients, throwing a specific .NET Framework exception is better than using a generic exception. Consider that managed clients as well as unmanaged clients can use your .NET Framework object, and throwing an HRESULT to a managed caller is less comprehensible than throwing an exception.
|Data Data Data Data||
Gets a collection of key/value pairs that provide additional user-defined information about the exception.(Inherited from Exception)
|ErrorCode ErrorCode ErrorCode ErrorCode||
|HelpLink HelpLink HelpLink HelpLink||
Gets or sets a link to the help file associated with this exception.(Inherited from Exception)
|HResult HResult HResult HResult||
Gets or sets HRESULT, a coded numerical value that is assigned to a specific exception.(Inherited from Exception)
|InnerException InnerException InnerException InnerException||
Gets the Exception instance that caused the current exception.(Inherited from Exception)
|Message Message Message Message||
Gets a message that describes the current exception.(Inherited from Exception)
|Source Source Source Source||
Gets or sets the name of the application or the object that causes the error.(Inherited from Exception)
|StackTrace StackTrace StackTrace StackTrace||
Gets a string representation of the immediate frames on the call stack.(Inherited from Exception)
|TargetSite TargetSite TargetSite TargetSite||
Gets the method that throws the current exception.(Inherited from Exception)
|SerializeObjectState SerializeObjectState SerializeObjectState SerializeObjectState||
Occurs when an exception is serialized to create an exception state object that contains serialized data about the exception.(Inherited from Exception)