如何在C#下通过winapi获取默认播放设备ID？

在C#下通过winapi获取默认播放设备ID，可以使用Core Audio API来实现。以下是一种实现方式：

首先，需要引入System.Runtime.InteropServices命名空间，以便使用DllImport特性来调用winapi函数。

然后，定义以下两个winapi函数的签名：

[DllImport("ole32.dll")]
static extern int CoInitialize(IntPtr pvReserved);

[DllImport("ole32.dll")]
static extern void CoUninitialize();

[DllImport("MMDeviceAPI.dll")]
static extern int MMDeviceEnumerator([MarshalAs(UnmanagedType.Interface)] out IMMDeviceEnumerator ppDeviceEnumerator);

[Guid("BCDE0395-E52F-467C-8E3D-C4579291692E"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IMMDeviceEnumerator
{
    int EnumAudioEndpoints(EDataFlow dataFlow, int dwStateMask, out IMMDeviceCollection ppDevices);
    int GetDefaultAudioEndpoint(EDataFlow dataFlow, ERole role, out IMMDevice ppEndpoint);
}

[Guid("A95664D2-9614-4F35-A746-DE8DB63617E6"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IMMDeviceCollection
{
    int GetCount(out int pcDevices);
    int Item(int nDevice, out IMMDevice ppDevice);
}

[Guid("D666063F-1587-4E43-81F1-B948E807363F"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IMMDevice
{
    int Activate(ref Guid iid, int dwClsCtx, IntPtr pActivationParams, [MarshalAs(UnmanagedType.IUnknown)] out object ppInterface);
    int GetId([MarshalAs(UnmanagedType.LPWStr)] out string ppstrId);
}

enum EDataFlow
{
    eRender,
    eCapture,
    eAll,
    EDataFlow_enum_count
}

enum ERole
{
    eConsole,
    eMultimedia,
    eCommunications,
    ERole_enum_count
}

接下来，编写获取默认播放设备ID的方法：

static string GetDefaultPlaybackDeviceId()
{
    CoInitialize(IntPtr.Zero);

    IMMDeviceEnumerator deviceEnumerator;
    int result = MMDeviceEnumerator(out deviceEnumerator);
    if (result != 0)
    {
        CoUninitialize();
        throw new Exception("Failed to get device enumerator");
    }

    IMMDevice defaultDevice;
    result = deviceEnumerator.GetDefaultAudioEndpoint(EDataFlow.eRender, ERole.eMultimedia, out defaultDevice);
    if (result != 0)
    {
        Marshal.ReleaseComObject(deviceEnumerator);
        CoUninitialize();
        throw new Exception("Failed to get default audio endpoint");
    }

    string deviceId;
    result = defaultDevice.GetId(out deviceId);
    if (result != 0)
    {
        Marshal.ReleaseComObject(defaultDevice);
        Marshal.ReleaseComObject(deviceEnumerator);
        CoUninitialize();
        throw new Exception("Failed to get device ID");
    }

    Marshal.ReleaseComObject(defaultDevice);
    Marshal.ReleaseComObject(deviceEnumerator);
    CoUninitialize();

    return deviceId;
}

调用GetDefaultPlaybackDeviceId方法即可获取默认播放设备的ID。

这种方法使用了Core Audio API来获取默认播放设备的ID，它可以在C#中直接调用winapi函数，通过COM接口与系统交互，实现获取设备信息的功能。

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