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Marshal.GetIUnknownForObject Method

Returns an IUnknown interface from a managed object.

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

public static IntPtr GetIUnknownForObject (
	Object o
)
public static IntPtr GetIUnknownForObject (
	Object o
)
public static function GetIUnknownForObject (
	o : Object
) : IntPtr
Not applicable.

Parameters

o

The object whose IUnknown interface is requested.

Return Value

The IUnknown pointer for the o parameter.

In managed code, you seldom work directly with the IUnknown interface. However, GetIUnknownForObject is useful when calling a method that exposes a COM object parameter as an IntPtr type, or with custom marshaling. Calling an object with this method causes the reference count to increment on the interface pointer before the pointer is returned. Always use Marshal.Release to decrement the reference count once you have finished with the pointer. This method provides the opposite functionality of the Marshal.GetObjectForIUnknown method.

You can also use this method on a managed object to obtain an interface pointer to the COM callable wrapper for the object. For additional information, see COM Callable Wrapper.

NoteNote:

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.

The following code example demonstrates how to retrieve an IUnknown interface for a managed object using the GetIUnknownForObject method.

using System;
using System.Runtime.InteropServices;

class Program
{

    static void Run()
    {

        // Create an int object
        int obj = 1;

        Console.WriteLine("Calling Marshal.GetIUnknownForObject...");

        // Get the IUnKnown pointer for the Integer object
        IntPtr pointer = Marshal.GetIUnknownForObject(obj);

        Console.WriteLine("Calling Marshal.Release...");

        // Always call Marshal.Release to decrement the reference count.
        Marshal.Release(pointer);
    }

    static void Main(string[] args)
    {
        Run();
    }
}

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

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0
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