System.Runtime.InteropServices.COMException Class

Summary

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

C# Syntax:

[Serializable] public class COMException : ExternalException

The HRESULT field contains the HRESULT returned by the callee. The COMException class can also be used to return specific HRESULT's to unmanaged clients.

System.Runtime.InteropServices Namespace | Exception | MSDN: handlingthrowingexceptions

System.Runtime.InteropServices.COMException Member List:

Public Constructors

ctor #1	Overloaded: .ctor() Default constructor. This constructor is called by derived class constructors to initialize state in this type. Initializes a new instance of the COMException class with default values.
ctor #2	Overloaded: .ctor(string message) Initializes a new instance of COMException with a specified message.
ctor #4	Overloaded: .ctor(string message, Exception inner) 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.
ctor #5	Overloaded: .ctor(string message, int errorCode) Initializes a new instance of COMException with a specified message and error code.

Public Properties

ErrorCode (inherited from System.Runtime.InteropServices.ExternalException)	Read-only See base class member description: System.Runtime.InteropServices.ExternalException.ErrorCode Gets the HRESULT of the error.
HelpLink (inherited from System.Exception)	Read-write See base class member description: System.Exception.HelpLink Gets or sets a link to the help file associated with this exception.
InnerException (inherited from System.Exception)	Read-only See base class member description: System.Exception.InnerException Gets the Exception instance that caused the current exception.
Message (inherited from System.Exception)	Read-only See base class member description: System.Exception.Message Gets a message that describes the current exception.
Source (inherited from System.Exception)	Read-write See base class member description: System.Exception.Source Gets or sets the name of the application or the object that causes the error.
StackTrace (inherited from System.Exception)	Read-only See base class member description: System.Exception.StackTrace Gets a string representation of the frames on the call stack at the time the current exception was thrown.
TargetSite (inherited from System.Exception)	Read-only See base class member description: System.Exception.TargetSite Gets the method that throws the current exception.

Public Methods

Equals (inherited from System.Object)	See base class member description: System.Object.Equals Derived from System.Object, the primary base class for all objects.
GetBaseException (inherited from System.Exception)	See base class member description: System.Exception.GetBaseException When overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions.
GetHashCode (inherited from System.Object)	See base class member description: System.Object.GetHashCode Derived from System.Object, the primary base class for all objects.
GetObjectData (inherited from System.Exception)	See base class member description: System.Exception.GetObjectData When overridden in a derived class, sets the SerializationInfo with information about the exception.
GetType (inherited from System.Object)	See base class member description: System.Object.GetType Derived from System.Object, the primary base class for all objects.
ToString	Overridden: Converts the contents of the exception to a string.

Protected Constructors

ctor #3

Overloaded: .ctor(SerializationInfo info, StreamingContext context) Initializes a new instance of the COMException class from serialization data.

Protected Properties

HResult (inherited from System.Exception)

Read-write See base class member description: System.Exception.HResult Gets or sets HRESULT, a coded numerical value that is assigned to a specific exception.

Protected Methods

Finalize (inherited from System.Object)	See base class member description: System.Object.Finalize Derived from System.Object, the primary base class for all objects.
MemberwiseClone (inherited from System.Object)	See base class member description: System.Object.MemberwiseClone Derived from System.Object, the primary base class for all objects.

Hierarchy:

• System.Object
• System.Exception
• System.SystemException
• System.Runtime.InteropServices.ExternalException
• System.Runtime.InteropServices.COMException

System.Runtime.InteropServices.COMException Member Details

Summary

Initializes a new instance of the COMException class with default values.

Default constructor. This constructor is called by derived class constructors to initialize state in this type.

C# Syntax:

public COMException();

COMException inherits from ExternalException. This constructor sets the properties of the Exception object as shown in the following table.

Property	Value
Exception.InnerException	null .
Exception.Message	A localized error message string.

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Summary

Initializes a new instance of COMException with a specified message.

C# Syntax:

public COMException(    string message );

message

The message that indicates the reason for the exception.

COMException inherits from ExternalException. This constructor sets the properties of the Exception object as shown in the following table.

Property	Value
Exception.InnerException	null .
Exception.Message

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Summary

Initializes a new instance of the COMException class from serialization data.

C# Syntax:

protected COMException(    SerializationInfo info,    StreamingContext context );

info

The object that holds the serialized object data.

context

The contextual information about the source or destination.

Exceptions

Exception Type	Condition
ArgumentNullException	info is null.

This constructor is called during deserialization to reconstitute the exception object transmitted over a stream. For more information, see the conceptual topic at MSDN: serialization.

COMException inherits from ExternalException.

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Summary

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.

C# Syntax:

public COMException(    string message,    Exception inner );

message

The error message that explains the reason for the exception.

inner

The exception that is the cause of the current exception. If the inner parameter is not null, the current exception is raised in a catch block that handles the inner exception.

An exception that is thrown as a direct result of a previous exception should include a reference to the previous exception in the Exception.InnerException property. The Exception.InnerException property returns the same value that is passed into the constructor, or null if the Exception.InnerException property does not supply the inner exception value to the constructor.

The following table shows the initial property values for an instance of COMException.

Property	Value
Exception.InnerException	The inner exception reference.
Exception.Message	The error message string.

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Summary

Initializes a new instance of COMException with a specified message and error code.

C# Syntax:

public COMException(    string message,    int errorCode );

message

The message that indicates the reason the exception occurred.

errorCode

The error code (HRESULT) value associated with this exception.

This COMException constructor sets the base message with the error code.

COMException inherits from ExternalException. This constructor sets the properties of the Exception object as shown in the following table.

Property	Value
Exception.InnerException	null .
Exception.Message

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Inherited
See base class member description: System.Runtime.InteropServices.ExternalException.ErrorCode

Summary

Gets the HRESULT of the error.

C# Syntax:

public virtual int ErrorCode {get;}

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Inherited
See base class member description: System.Exception.HelpLink

Summary

Gets or sets a link to the help file associated with this exception.

C# Syntax:

public virtual string HelpLink {get; set;}

The return value, which represents a help file, is a URN or URL. For example, the HelpLink value could be:

"file:///C:/Applications/Bazzal/help.html#ErrorNum42"

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Inherited
See base class member description: System.Exception.HResult

Summary

Gets or sets HRESULT, a coded numerical value that is assigned to a specific exception.

C# Syntax:

protected int HResult {get; set;}

HRESULT is a 32-bit value, divided into three different fields: a severity code, a facility code, and an error code. The severity code indicates whether the return value represents information, warning, or error. The facility code identifies the area of the system responsible for the error. The error code is a unique number that is assigned to represent the exception. Each exception is mapped to a distinct HRESULT. When managed code throws an exception, the runtime passes the HRESULT to the COM client. When unmanaged code returns an error, the HRESULT is converted to an exception, which is then thrown by the runtime.

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Inherited
See base class member description: System.Exception.InnerException

Summary

Gets the Exception instance that caused the current exception.

C# Syntax:

public Exception InnerException {get;}

When an exception X is thrown as a direct result of a previous exception Y, the InnerException property of X should contain a reference to Y.

Use the InnerException property to obtain the set of exceptions that led to the current exception.

You can create a new exception that catches an earlier exception. The code that handles the second exception can make use of the additional information from the earlier exception to handle the error more appropriately.

Suppose that there is a function that reads a file and formats the data from that file. In this example, as the code tries to read the file, an IOException is thrown. The function catches the IOException and throws a FileNotFoundException. The IOException could be saved in the Exception.InnerException property of the FileNotFoundException, enabling the code that catches the FileNotFoundException to examine what causes the initial error.

The Exception.InnerException property, which holds a reference to the inner exception, is set upon initialization of the exception object.

The following example demonstrates throwing and catching an exception that references an inner exception.

using System;
public class MyAppException:ApplicationException 
{
   public MyAppException (String message) : base (message) 
   {}
   public MyAppException (String message, Exception inner) : base(message,inner) {}	
   }
public class ExceptExample 
{
   public void ThrowInner () 
   {
   throw new MyAppException("ExceptExample inner exception");
   }
   public void CatchInner() 
   {
      try 
      {
      this.ThrowInner();
      }
         catch (Exception e) 
         {
         throw new MyAppException("Error caused by trying ThrowInner.",e);
         }
      }
   }
public class Test 
{
   public static void Main() 
   {
   ExceptExample testInstance = new ExceptExample();
      try 
      {
      testInstance.CatchInner();
      }
         catch(Exception e) 
         {
         Console.WriteLine ("In Main catch block. Caught: {0}", e.Message);
         Console.WriteLine ("Inner Exception is {0}",e.InnerException);
         }
      }
}

    

This code has the following output:

In Main catch block. Caught: Error caused by trying ThrowInner. Inner Exception is MyAppException: ExceptExample inner exception at ExceptExample.ThrowInner() at ExceptExample.CatchInner()

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Inherited
See base class member description: System.Exception.Message

Summary

Gets a message that describes the current exception.

C# Syntax:

public virtual string Message {get;}

The text of Message should completely describe the error and should, when possible, explain how to correct it. The value of the Message property is included in the information returned by Exception.ToString.

The Message property is set only when creating an Exception. If no message was supplied to the constructor for the current instance, the system supplies a default message that is formatted using the current system culture.

Notes to inheritors: The Message property is overridden in classes that require control over message content or format. Application code typically accesses this property when it needs to display information about an exception that has been caught.

The error message should be localized.

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Inherited
See base class member description: System.Exception.Source

Summary

Gets or sets the name of the application or the object that causes the error.

C# Syntax:

public virtual string Source {get; set;}

If Exception.Source is not set, the name of the assembly where the exception originated is returned.

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Inherited
See base class member description: System.Exception.StackTrace

Summary

Gets a string representation of the frames on the call stack at the time the current exception was thrown.

C# Syntax:

public virtual string StackTrace {get;}

The execution stack keeps track of all the methods that are in execution at a given instant. A trace of the method calls is called a stack trace. The stack trace listing provides a means to follow the call sequence to the line number in the method where the exception occurs.

StackTrace may not report as many method calls as expected, due to code transformations, such as inlining, that occur during optimization.

Notes to inheritors: The StackTrace property is overridden in classes that require control over the stack trace content or format.

By default, the stack trace is captured immediately before an exception object is thrown. Use Environment.StackTrace to get stack trace information when no exception is being thrown.

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Inherited
See base class member description: System.Exception.TargetSite

Summary

Gets the method that throws the current exception.

C# Syntax:

public MethodBase TargetSite {get;}

If the method that throws this exception is not available and the stack trace is not a null reference (not set or empty), Exception.TargetSite obtains the method from the stack trace. If the stack trace is a null reference , Exception.TargetSite also returns a null reference.

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Inherited
See base class member description: System.Object.Equals

C# Syntax:

public virtual bool Equals(    object obj );

For more information on members inherited from System.Object click on the link above.

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Inherited
See base class member description: System.Object.Finalize

C# Syntax:

~COMException();

For more information on members inherited from System.Object click on the link above.

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Inherited
See base class member description: System.Exception.GetBaseException

Summary

When overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions.

C# Syntax:

public virtual Exception GetBaseException();

Return Value:

The first exception thrown in a chain of exceptions. If the Exception.InnerException property of the current exception is a null reference (not set or empty), this property returns the current exception.

A chain of exceptions consists of a set of exceptions such that each exception in the chain was thrown as a direct result of the exception referenced in its InnerException property. For a given chain, there can be exactly one exception that is the root cause of all other exceptions in the chain. This exception is called the base exception and its InnerException property always contains a null reference.

For all exceptions in a chain of exceptions, the GetBaseException method must return the same object (the base exception).

Use the GetBaseException method when you want to find the root cause of an exception but do not need information about exceptions that may have occurred between the current exception and the first exception.

Notes to inheritors: The GetBaseException method is overridden in classes that require control over the exception content or format.

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Inherited
See base class member description: System.Object.GetHashCode

C# Syntax:

public virtual int GetHashCode();

For more information on members inherited from System.Object click on the link above.

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Inherited
See base class member description: System.Exception.GetObjectData

Summary

When overridden in a derived class, sets the SerializationInfo with information about the exception.

C# Syntax:

public virtual void GetObjectData(    SerializationInfo info,    StreamingContext context );

info

The SerializationInfo that holds the serialized object data about the exception being thrown.

context

The StreamingContext that contains contextual information about the source or destination.

Exceptions

Exception Type	Condition
ArgumentNullException	The info parameter is a null reference (not set or empty).

Implements:

ISerializable.GetObjectData

GetObjectData sets a SerializationInfo with all the exception object data targeted for serialization. During deserialization, the exception is reconstituted from the SerializationInfo transmitted over the stream.

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Inherited
See base class member description: System.Object.GetType

C# Syntax:

public Type GetType();

For more information on members inherited from System.Object click on the link above.

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Inherited
See base class member description: System.Object.MemberwiseClone

C# Syntax:

protected object MemberwiseClone();

For more information on members inherited from System.Object click on the link above.

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Summary

Converts the contents of the exception to a string.

C# Syntax:

public override string ToString();

Return Value:

A string containing the Exception.HResult, Exception.Message, Exception.InnerException, and Exception.StackTrace properties of the exception.

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