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UniqueComInterfaceMarshaller.cs
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UniqueComInterfaceMarshaller.cs
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Runtime.Versioning;
namespace System.Runtime.InteropServices.Marshalling
{
/// <summary>
/// COM interface marshaller using a StrategyBasedComWrappers instance
/// that will only create unique native object wrappers (RCW).
/// </summary>
/// <remarks>
/// This marshaller will always pass the <see cref="CreateObjectFlags.Unwrap"/> and <see cref="CreateObjectFlags.UniqueInstance"/> flags
/// to <see cref="ComWrappers.GetOrCreateObjectForComInstance(IntPtr, CreateObjectFlags)"/>.
/// </remarks>
/// <typeparam name="T">The managed type that represents a COM interface type</typeparam>
[UnsupportedOSPlatform("android")]
[UnsupportedOSPlatform("browser")]
[UnsupportedOSPlatform("ios")]
[UnsupportedOSPlatform("tvos")]
[CLSCompliant(false)]
[CustomMarshaller(typeof(CustomMarshallerAttribute.GenericPlaceholder), MarshalMode.Default, typeof(UniqueComInterfaceMarshaller<>))]
public static unsafe class UniqueComInterfaceMarshaller<T>
{
/// <summary>
/// Convert a managed object to a COM interface pointer for the COM interface represented by <typeparamref name="T"/>.
/// </summary>
/// <param name="managed">The managed object</param>
/// <returns>The COM interface pointer</returns>
public static void* ConvertToUnmanaged(T? managed)
{
if (managed == null)
{
return null;
}
if (!ComWrappers.TryGetComInstance(managed, out nint unknown))
{
unknown = StrategyBasedComWrappers.DefaultMarshallingInstance.GetOrCreateComInterfaceForObject(managed, CreateComInterfaceFlags.None);
}
return ComInterfaceMarshaller<T>.CastIUnknownToInterfaceType(unknown);
}
/// <summary>
/// Convert a COM interface pointer to a managed object.
/// </summary>
/// <param name="unmanaged">The COM interface pointer</param>
/// <returns>A managed object that represents the passed in COM interface pointer.</returns>
/// <remarks>
/// If the passed in COM interface pointer wraps a managed object, this method returns the underlying object.
/// </remarks>
public static T? ConvertToManaged(void* unmanaged)
{
if (unmanaged == null)
{
return default;
}
return (T)StrategyBasedComWrappers.DefaultMarshallingInstance.GetOrCreateObjectForComInstance((nint)unmanaged, CreateObjectFlags.Unwrap | CreateObjectFlags.UniqueInstance);
}
/// <summary>
/// Release a reference to the COM interface pointer.
/// </summary>
/// <param name="unmanaged">A COM interface pointer.</param>
public static void Free(void* unmanaged)
{
if (unmanaged != null)
{
Marshal.Release((nint)unmanaged);
}
}
}
}