Question

我正在尝试将以下方法从C ++转换为C＃

HRESULT GetDevices(
  [in, out]  LPWSTR *pPnPDeviceIDs,
  [in, out]  DWORD *pcPnPDeviceIDs
);

在MSDN文档中说：

pPnPDeviceIDs [in，out]
  调用者分配的字符串指针数组，包含所有连接设备的即插即用名称。要了解此参数所需的大小，请首先调用此方法，并将此参数设置为NULL并将pcPnPDeviceIDs设置为零，然后根据pcPnPDeviceIDs检索的值分配缓冲区。

pcPnPDeviceIDs [in，out]   输入时，pPnPDeviceIDs可以容纳的值的数量。在输出时，指向实际写入pPnPDeviceIDs的设备数量的指针。

到目前为止，我有这个定义：

[PreserveSig]        
int GetDevices(    
    [In, Out] IntPtr pPnPDeviceIDs,
    [In, Out] ref uint pcPnPDeviceIDs
);

我尝试为Marshal.AllocCoTaskMem分配一些带有pPnPDeviceIDs的内存，但是当我尝试调用该方法时，我得到了一个AccessViolationException。

有人能告诉我转换LPWSTR *字符串指针数组的正确方法吗？

编辑：以下是我的定义：

[ComImport, System.Security.SuppressUnmanagedCodeSecurity,
InterfaceType(ComInterfaceType.InterfaceIsIUnknown),
Guid("a1567595-4c2f-4574-a6fa-ecef917b9a40")]
public interface IPortableDeviceManager
{
    [PreserveSig]
    HRESULT GetDeviceDescription(
        [In] string pszPnpDeviceID,
        [In, Out] ref StringBuilder pDeviceDescription,
        [In, Out] ref uint pcchDeviceDescription);

    [PreserveSig]
    HRESULT GetDeviceFriendlyName(
        [In] string pszPnPDeviceID,
        [In, Out] ref StringBuilder pDeviceFriendlyName,
        [In, Out] ref uint pcchDeviceFriendlyName);

    [PreserveSig]
    HRESULT GetDeviceManufacturer(
        [In] string pszPnPDeviceID,
        [In, Out] ref StringBuilder pDeviceManufacturer,
        [In, Out] ref uint pcchDeviceManufacturer);

    [PreserveSig]
    HRESULT GetDeviceProperty(
        [In] string pszPnPDeviceID,
        [In] string pszDevicePropertyName,
        [In, Out] IntPtr pData,
        [In, Out] ref uint pcbData,
        [In, Out] ref uint pdwType);

    [PreserveSig]        
    HRESULT GetDevices(     
        [In, Out] IntPtr pPnPDeviceIDs,
        [In, Out] ref uint pcPnPDeviceIDs);


    [PreserveSig]
    HRESULT GetPrivateDevices(
        [In, Out] IntPtr pPnPDeviceIDs,
        [In, Out] ref uint pcPnPDeviceIDs);

    [PreserveSig]
    HRESULT RefreshDeviceList();
}

/// <summary>
/// CLSID_PortableDeviceManager
/// </summary>
[ComImport, Guid("0af10cec-2ecd-4b92-9581-34f6ae0637f3")]
public class CLSID_PortableDeviceManager { }

这是我的测试代码：

var devManager = Activator.CreateInstance(
            typeof(CLSID_PortableDeviceManager)) as IPortableDeviceManager;

        uint pcPnPDeviceIDs = 0;
        var res1 = devManager.GetDevices(IntPtr.Zero, ref pcPnPDeviceIDs);
        // check for errors in res1
        IntPtr ptr = IntPtr.Zero;

        try
        {
            ptr = Marshal.AllocCoTaskMem((int)(IntPtr.Size * pcPnPDeviceIDs));
            var res2 = devManager.GetDevices(ptr, ref pcPnPDeviceIDs);
            // check for errors in res2

            IntPtr ptr2 = ptr;

            for (uint i = 0; i < pcPnPDeviceIDs; i++)
            {
                string str = Marshal.PtrToStringUni(ptr2);
                ptr2 += IntPtr.Size;
            }
        }
        finally
        {
            if (ptr != IntPtr.Zero)
            {
                Marshal.FreeCoTaskMem(ptr);
            }
        }

        Marshal.ReleaseComObject(devManager);

第二次调用GetDevices（）

时出现AccessViolationException

Answer 1

试试这个：

uint pcPnPDeviceIDs = 0;
int res1 = GetDevices(IntPtr.Zero, ref pcPnPDeviceIDs);
// check for errors in res1

IntPtr ptr = IntPtr.Zero;

try
{
    ptr = Marshal.AllocCoTaskMem((int)(IntPtr.Size * pcPnPDeviceIDs));
    int res2 = GetDevices(ptr, ref pcPnPDeviceIDs);
    // check for errors in res2

    IntPtr ptr2 = ptr;

    for (uint i = 0; i < pcPnPDeviceIDs; i++)
    {
        string str = Marshal.PtrToStringUni(Marshal.ReadIntPtr(ptr2));
        ptr2 += IntPtr.Size;
    }
}
finally
{
    if (ptr != IntPtr.Zero)
    {
        IntPtr ptr2 = ptr;

        for (uint i = 0; i < pcPnPDeviceIDs; i++)
        {
            Marshal.FreeCoTaskMem(Marshal.ReadIntPtr(ptr2));
            ptr2 += IntPtr.Size;
        }

        Marshal.FreeCoTaskMem(ptr);
    }
}

我使用uint（s）用于HRESULT，因为它们必须逐位解析（对于无符号整数，它更容易）
系统内存的分配应始终受try/finally保护。并记得释放所有字符串:-)（正如我所做的那样）

使用IntPtr[]的变体：

GetDevices的定义（注意使用[MarshalAs(UnmanagedType.LPArray)]：

[PreserveSig]
HRESULT GetDevices(
    [In][MarshalAs(UnmanagedType.LPArray)] IntPtr[] pPnPDeviceIDs,
    [In, Out] ref uint pcPnPDeviceIDs);

剩下的代码：

var devManager = Activator.CreateInstance(typeof(CLSID_PortableDeviceManager)) as IPortableDeviceManager;
uint pcPnPDeviceIDs = 0;
HRESULT res1 = devManager.GetDevices(null, ref pcPnPDeviceIDs);
// check for errors in res1

IntPtr[] ptr = null;

try
{
    ptr = new IntPtr[pcPnPDeviceIDs];

    HRESULT res2 = devManager.GetDevices(ptr, ref pcPnPDeviceIDs);
    // check for errors in res2

    for (uint i = 0; i < pcPnPDeviceIDs; i++)
    {
        string str = Marshal.PtrToStringUni(ptr[i]);
    }
}
finally
{
    if (ptr != null)
    {
        for (uint i = 0; i < pcPnPDeviceIDs; i++)
        {
            Marshal.FreeCoTaskMem(ptr[i]);
        }
    }
}

通过这种方式，您不必在非托管内存中分配主数组。

将LPWSTR *字符串指针数组转换为C＃

1 个答案: