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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