Marshal.ReleaseComObject Method (System.Runtime.InteropServices)

ReleaseComObject Method

Collapse All

Language Filter

This page is specific to

Microsoft Visual Studio 2008/.NET Framework 3.5

Other versions are also available for the following:

.NET Framework Class Library

Marshal..::.ReleaseComObject Method

Updated: November 2007

Decrements the reference count of the supplied runtime callable wrapper.

Namespace: System.Runtime.InteropServices
Assembly: mscorlib (in mscorlib.dll)

Syntax

Visual Basic (Declaration)

<SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags := SecurityPermissionFlag.UnmanagedCode)> _
Public Shared Function ReleaseComObject ( _
    o As Object _
) As Integer

Visual Basic (Usage)

Dim o As Object
Dim returnValue As Integer

returnValue = Marshal.ReleaseComObject(o)

[SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
public static int ReleaseComObject(
    Object o
)

Visual C++

[SecurityPermissionAttribute(SecurityAction::LinkDemand, Flags = SecurityPermissionFlag::UnmanagedCode)]
public:
static int ReleaseComObject(
    Object^ o
)

/** @attribute SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode) */
public static int ReleaseComObject(
    Object o
)

JScript

public static function ReleaseComObject(
    o : Object
) : int

Parameters

o: Type: System..::.Object
The COM object to release.

Return Value

Type: System..::.Int32

The new value of the reference count of the runtime callable wrapper associated with o. This value is typically zero since the runtime callable wrapper keeps just one reference to the wrapped COM object regardless of the number of managed clients calling it.

Exceptions

Exception	Condition
ArgumentException	o is not a valid COM object. -or- o is nullNothingnullptra null reference (Nothing in Visual Basic).

Exception

Condition

ArgumentException

o is not a valid COM object.

-or-

o is nullNothingnullptra null reference (Nothing in Visual Basic).

Remarks

Every time a COM interface pointer enters the common language runtime, it is wrapped in a runtime callable wrapper. If you are unfamiliar with the features of this wrapper, see Runtime Callable Wrapper.

This method is used to explicitly control the lifetime of a COM object used from managed code. You should use this method to free the underlying COM object that holds references to resources in a timely manner or when objects must be freed in a specific order.

The runtime callable wrapper has a reference count that is incremented every time a COM interface pointer is mapped to it. The ReleaseComObject method decrements the reference count of a runtime callable wrapper. When the reference count reached zero, the runtime releases all its references on the unmanaged COM object, and throws a System..::.NullReferenceException if you attempt to use the object further. If the same COM interface is passed more than once from unmanaged to managed code, the reference count on the wrapper is incremented every time and calling ReleaseComObject returns the number of remaining references.

Note:
To ensure that the runtime callable wrapper and the original COM object are released, construct a loop from which you call this method until the returned reference count reaches zero.

Note:
This method uses SecurityAction..::.LinkDemand to prevent it from being called from untrusted code; only the immediate caller is required to have SecurityPermissionAttribute..::.UnmanagedCode permission. If your code can be called from partially trusted code, do not pass user input to Marshal class methods without validation. For important limitations on using the LinkDemand member, see Demand vs. LinkDemand.

Note:

This method uses SecurityAction..::.LinkDemand to prevent it from being called from untrusted code; only the immediate caller is required to have SecurityPermissionAttribute..::.UnmanagedCode permission. If your code can be called from partially trusted code, do not pass user input to Marshal class methods without validation. For important limitations on using the LinkDemand member, see Demand vs. LinkDemand.

Permissions

SecurityPermission
for permission to call unmanaged code.
Associated enumeration: UnmanagedCode Security action: LinkDemand

Platforms

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information