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HandleRef Structure

Wraps a managed object holding a handle to a resource that is passed to unmanaged code using platform invoke.

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

[ComVisibleAttribute(true)] 
public struct HandleRef
/** @attribute ComVisibleAttribute(true) */ 
public final class HandleRef extends ValueType
JScript suports the use of structures, but not the declaration of new ones.

If you use platform invoke to call a managed object, and the object is not referenced elsewhere after the platform invoke call, it is possible for the garbage collector to finalize the managed object. This action releases the resource and invalidates the handle, causing the platform invoke call to fail. Wrapping a handle with HandleRef guarantees that the managed object is not garbage collected until the platform invoke call completes. For a description of platform invoke services, see Consuming Unmanaged DLL Functions.

The HandleRef value type, like GCHandle, is a special type recognized by the interop marshaler. A normal, nonpinned GCHandle also prevents untimely garbage collection, yet HandleRef provides better performance. Although using HandleRef to keep an object alive for the duration of a platform invoke call is preferred, you can also use the GC.KeepAlive method for the same purpose.

The HandleRef constructor takes two parameters: an Object representing the wrapper, and an IntPtr representing the unmanaged handle. The interop marshaler passes only the handle to unmanaged code, and guarantees that the wrapper (passed as the first parameter to the constructor of the HandleRef) remains alive for the duration of the call.

The following example shows how to use HandleRef to keep alive an object passed as the first parameter. The interop marshaler passes only the handle to unmanaged code.

FileStream fs = new FileStream("HandleRef.txt", FileMode.Open);
HandleRef hr = new HandleRef(fs, fs.SafeFileHandle.DangerousGetHandle());
StringBuilder buffer = new StringBuilder(5);
int read = 0;

// platform invoke will hold reference to HandleRef until call ends

LibWrap.ReadFile(hr, buffer, 5, out read, 0);
Console.WriteLine("Read with struct parameter: {0}", buffer);

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

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

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