在 C# 中使用 SHAssocEnumHandlers

Question

我很难在 C# 中调用 WinAPI SHAssocEnumHandlers。

using System;
using System.Runtime.InteropServices;

namespace AssocHandlerTest
{
  [Flags]
  public enum ASSOC_FILTER
  {
    ASSOC_FILTER_NONE = 0x0,
    ASSOC_FILTER_RECOMMENDED = 0x1
  };

  [ComImport]
  [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
  [Guid("F04061AC-1659-4a3f-A954-775AA57FC083")]
  public interface IAssocHandler
  {
    int GetName([Out, MarshalAs(UnmanagedType.LPWStr)] out string ppsz);
    int GetUIName([Out, MarshalAs(UnmanagedType.LPWStr)] out string ppsz);
    int GetIconLocation([Out, MarshalAs(UnmanagedType.LPWStr)] out string ppszPath, [Out] out int pIndex);
    int IsRecommended();
    int MakeDefault([In, MarshalAs(UnmanagedType.LPWStr)] string pszDescription);
    int Invoke([In, MarshalAs(UnmanagedType.IUnknown)] object pdo);
    int CreateInvoker([In, MarshalAs(UnmanagedType.IUnknown)] object pdo, [Out, MarshalAs(UnmanagedType.IUnknown)] out object ppInvoker);
  };

  [ComImport]
  [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
  [Guid("973810ae-9599-4b88-9e4d-6ee98c9552da")]
  public interface IEnumAssocHandlers
  {
    int Next([In, MarshalAs(UnmanagedType.U4)] int celt, [Out, MarshalAs(UnmanagedType.Interface)] out IAssocHandler rgelt, [Out, MarshalAs(UnmanagedType.U4)] out int pceltFetched);
  };

  class Program
  {
    [DllImport("Shell32.dll", CharSet = CharSet.Auto)]
    static extern bool SHAssocEnumHandlers(
    [In, MarshalAs(UnmanagedType.LPWStr)] string pszExtra, [In] ASSOC_FILTER afFilter, [Out, MarshalAs(UnmanagedType.Interface)] out IEnumAssocHandlers ppEnumHandler);

    static void Main(string[] args)
    {
      const string extension = ".html";
      try
      {
        IEnumAssocHandlers enumAssocHandlers = null;
        SHAssocEnumHandlers(extension, ASSOC_FILTER.ASSOC_FILTER_NONE, out enumAssocHandlers);
      }
      catch (Exception ex)
      {
        Console.WriteLine(ex.Message);
      }
      Console.ReadLine();
    }
  }
}

调用 SHAssocEnumHandlers 时我只得到一个

"Unexpected error: HRESULT: 0x80004005 (E_FAIL)"

堆栈跟踪显示

处的异常

System.StubHelpers.InterfaceMarshaler.ConvertToManaged(IntPtr pUnk, IntPtr itfMT, IntPtr classMT, Int32 flags)

我想我可能缺少一些实现。但是我想不通是什么。

更新 1

此错误只发生在 Windows 7 上。在 Windows 10 机器上它工作正常。（在各种win7和win10机器上测试过）

Answer 1

我找到了一种在 Windows 7 机器上获得结果的方法。

这样你就可以复习指针了。

我不是 100% 确定它为什么有效。而且我确信这不是最安全的方法。

using System;
using System.Runtime.InteropServices;

namespace AssocHandlerWithPointer
{
  [Flags]
  public enum ASSOC_FILTER
  {
    ASSOC_FILTER_NONE = 0x00000000,
    ASSOC_FILTER_RECOMMENDED = 0x00000001
  }

  public class Test
  {
    [DllImport("Shell32", EntryPoint = "SHAssocEnumHandlers", PreserveSig = false)]
    public extern static void SHAssocEnumHandlers([MarshalAs(UnmanagedType.LPWStr)] string pszExtra, ASSOC_FILTER afFilter, [Out] out IntPtr ppEnumHandler);

    // IEnumAssocHandlers
    [UnmanagedFunctionPointer(CallingConvention.Winapi, CharSet = CharSet.Unicode)]
    private delegate int FuncNext(IntPtr refer, int celt, [Out, MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.Interface, SizeParamIndex = 1)] IntPtr[] rgelt, [Out] out int pceltFetched);

    // IAssocHandler
    [UnmanagedFunctionPointer(CallingConvention.Winapi, CharSet = CharSet.Unicode)]
    private delegate int FuncGetName(IntPtr refer, out IntPtr ppsz);

    [UnmanagedFunctionPointer(CallingConvention.Winapi, CharSet = CharSet.Unicode)]
    private delegate int FuncGetUiName(IntPtr refer, out IntPtr ppsz);  


    static void Main(string[] args)
    {
      const string extension = ".html";

      IntPtr pEnumAssocHandlers;
      SHAssocEnumHandlers(extension, ASSOC_FILTER.ASSOC_FILTER_RECOMMENDED, out pEnumAssocHandlers);

      IntPtr pFuncNext = Marshal.ReadIntPtr(Marshal.ReadIntPtr(pEnumAssocHandlers) + 3 * sizeof(int));
      FuncNext next = (FuncNext)Marshal.GetDelegateForFunctionPointer(pFuncNext, typeof(FuncNext));

      IntPtr[] pArrayAssocHandlers  = new IntPtr[255];
      int num;

      int resNext = next(pEnumAssocHandlers, 255, pArrayAssocHandlers, out num);
      if (resNext == 0)
      {
        for (int i = 0; i < num; i++)
        {
          IntPtr pAssocHandler = pArrayAssocHandlers[i];
          IntPtr pFuncGetName = Marshal.ReadIntPtr(Marshal.ReadIntPtr(pAssocHandler) + 3 * sizeof(int));
          FuncGetName getName = (FuncGetName)Marshal.GetDelegateForFunctionPointer(pFuncGetName, typeof(FuncGetName));
          IntPtr pName;
          int resGetName = getName(pAssocHandler, out pName);
          Console.WriteLine("Path: " + Marshal.PtrToStringUni(pName));

          IntPtr pFuncGetUiName = Marshal.ReadIntPtr(Marshal.ReadIntPtr(pAssocHandler) + 4 * sizeof(int));
          FuncGetUiName getUiName = (FuncGetUiName)Marshal.GetDelegateForFunctionPointer(pFuncGetUiName, typeof(FuncGetUiName));
          IntPtr pUiName;
          int resGetUiName = getUiName(pAssocHandler, out pUiName);
          Console.WriteLine("UIName: " + Marshal.PtrToStringUni(pUiName));

          Marshal.Release(pArrayAssocHandlers[i]);
        }
      }
      Marshal.Release(pEnumAssocHandlers);
      Console.ReadLine();
    }
  }
}

一些解释：

+ 3 * sizeof(int)

接口IEnumAssocHandlers和IAssocHandler继承自IUnknown。所以他们总是实现三个方法。这就是为什么您必须将指向第一个函数的指针移动 3。第二个函数的指针移动 + 4，依此类推。不确定这个解释是否正确，但它有效:)

IntPtr[] pArrayAssocHandlers  = new IntPtr[255];

Next 函数 returns IAssocHandler 数组。我发现无法找出给定扩展的 IAssocHandler 数量。所以我将数组的大小设置为 255.

Next 函数获取三个参数（在 NumberOfElementsToRetrieve 中，在 ArrayOfIAssocHandlers 中，在 NumberOfRetrievedElements 中）听起来有点奇怪，但这就是文档中的内容。

相关链接：
SHAssocEnumHandlers
IEnumAssocHandlers
IAssocHandler

注：
此示例中缺少各种错误处理。

在 C# 中使用 SHAssocEnumHandlers

Use SHAssocEnumHandlers in C#

c#

com

winapi

shell32

marshalling