COM对象C＃将MMDeviceEnumerator转换为IMMDeviceEnumerator InvalidCastException [英] COM Objects C# Casting MMDeviceEnumerator to IMMDeviceEnumerator InvalidCastException

问题描述

我没有使用COM Imports的经验，只是在使用别人的代码而对我不起作用

I have no experience with COM Imports and am just working with someone else's code that wasn't working for me

抛出InvalidCastException的代码行：

The line of code that is throwing the InvalidCastException:

    IMMDeviceEnumerator deviceEnumerator = (IMMDeviceEnumerator)(new MMDeviceEnumerator());

COM导入：

[Guid("BCDE0395-E52F-467C-8E3D-C4579291692E")]
internal class MMDeviceEnumerator
{
}

[Guid("A95664D2-9614-4F35-A746-DE8DB63617E6"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
internal interface IMMDeviceEnumerator
{
    [PreserveSig]
    int EnumAudioEndpoints(EDataFlow dataFlow, DEVICE_STATE dwStateMask, out IMMDeviceCollection ppDevices);

    [PreserveSig]
    int GetDefaultAudioEndpoint(EDataFlow dataFlow, ERole role, out IMMDevice ppEndpoint);

    [PreserveSig]
    int GetDevice([MarshalAs(UnmanagedType.LPWStr)] string pwstrId, out IMMDevice ppDevice);

    [PreserveSig]
    int RegisterEndpointNotificationCallback(IMMNotificationClient pClient);

    [PreserveSig]
    int UnregisterEndpointNotificationCallback(IMMNotificationClient pClient);
}

屏幕截图：

推荐答案

那不是很紧密，您正在创建.NET类。让CLR知道这实际上是一个COM声明，并且已在其他地方实现，需要使用[ComImport]指令。我将为您提供最少的必需声明：

That's not very close, you are creating a .NET class. Letting the CLR know that this is actually a COM declaration and implemented elsewhere requires using the [ComImport] directive. I'll give you the minimum required declarations:

[ComImport]
[Guid("A95664D2-9614-4F35-A746-DE8DB63617E6")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface IMMDeviceEnumerator
{
    // etc..
}

public static class MMDeviceEnumeratorFactory {
    private static readonly Guid MMDeviceEnumerator = new Guid("BCDE0395-E52F-467C-8E3D-C4579291692E");

    public static IMMDeviceEnumerator CreateInstance() {
        var type = Type.GetTypeFromCLSID(MMDeviceEnumerator);
        return (IMMDeviceEnumerator)Activator.CreateInstance(type);
    }
}

并像这样使用它：

IMMDeviceEnumerator deviceEnumerator = MMDeviceEnumeratorFactory.CreateInstance();

请务必避免使用[PreserveSig]，当方法失败时，您要大声敲打。请注意，该接口已经被NAudio库包装。

Do strongly avoid using [PreserveSig], you want a loud bang when a method fails. Do note that this interface is already wrapped by the NAudio library.

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