c# - 在 C# 中定义 Windows API 接口(interface)时，是否必须定义所有成员？我可以只定义我将要使用的方法吗？

Question

例如，这是 IFileOpenDialog 的完整定义界面，Windows Shell 界面，取自 Pinvoke网站:

[ComImport, Guid ( "d57c7288-d4ad-4768-be02-9d969532d960" ), InterfaceType ( ComInterfaceType.InterfaceIsIUnknown )]
interface IFileOpenDialog : IFileDialog
{
// Defined on IModalWindow - repeated here due to requirements of COM interop layer
// --------------------------------------------------------------------------------
[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime ), PreserveSig]
int Show ( [In] IntPtr parent );

// Defined on IFileDialog - repeated here due to requirements of COM interop layer
[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetFileTypes ( [In] uint cFileTypes, [In] COMDLG_FILTERSPEC[] rgFilterSpec );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetFileTypeIndex ( [In] uint iFileType );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void GetFileTypeIndex ( out uint piFileType );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void Advise ( [In, MarshalAs ( UnmanagedType.Interface )] IFileDialogEvents pfde, out uint pdwCookie );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void Unadvise ( [In] uint dwCookie );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetOptions ( [In] FOS fos );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void GetOptions ( out FOS pfos );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetDefaultFolder ( [In, MarshalAs ( UnmanagedType.Interface )] IShellItem psi );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetFolder ( [In, MarshalAs ( UnmanagedType.Interface )] IShellItem psi );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void GetFolder ( [MarshalAs ( UnmanagedType.Interface )] out IShellItem ppsi );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void GetCurrentSelection ( [MarshalAs ( UnmanagedType.Interface )] out IShellItem ppsi );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetFileName ( [In, MarshalAs ( UnmanagedType.LPWStr )] string pszName );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void GetFileName ( [MarshalAs ( UnmanagedType.LPWStr )] out string pszName );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetTitle ( [In, MarshalAs ( UnmanagedType.LPWStr )] string pszTitle );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetOkButtonLabel ( [In, MarshalAs ( UnmanagedType.LPWStr )] string pszText );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetFileNameLabel ( [In, MarshalAs ( UnmanagedType.LPWStr )] string pszLabel );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void GetResult ( [MarshalAs ( UnmanagedType.Interface )] out IShellItem ppsi );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void AddPlace ( [In, MarshalAs ( UnmanagedType.Interface )] IShellItem psi, NativeMethods.FDAP fdap );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetDefaultExtension ( [In, MarshalAs ( UnmanagedType.LPWStr )] string pszDefaultExtension );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void Close ( [MarshalAs ( UnmanagedType.Error )] int hr );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetClientGuid ( [In] ref Guid guid );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void ClearClientData ( );

// Not supported:  IShellItemFilter is not defined, converting to IntPtr
[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetFilter ( [MarshalAs ( UnmanagedType.Interface )] IntPtr pFilter );

// Defined by IFileOpenDialog
// ---------------------------------------------------------------------------------
[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void GetResults ( [MarshalAs ( UnmanagedType.Interface )] out IShellItemArray ppenum );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void GetSelectedItems ( [MarshalAs ( UnmanagedType.Interface )] out IShellItemArray ppsai );
}

如果我只打算使用这个接口(interface)中的两个方法，我可以这样定义它吗:

[ComImport, Guid ( "d57c7288-d4ad-4768-be02-9d969532d960" ), InterfaceType ( ComInterfaceType.InterfaceIsIUnknown )]
interface IFileOpenDialog : IFileDialog
{
// Defined on IModalWindow - repeated here due to requirements of COM interop layer
// --------------------------------------------------------------------------------
[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime ), PreserveSig]
int Show ( [In] IntPtr parent );

[MethodImpl ( MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime )]
void SetOptions ( [In] FOS fos );
}

它会起作用吗？还是我必须定义包含所有方法的完整接口(interface)？

Answer 1

不，这行不通。 CLR 根据声明为 COM 接口(interface)构建一个调度表。该表中函数指针的顺序由声明中方法定义的顺序设置。在这两种情况下，Show() 方法都会占据第一个位置，没有问题。然而，SetOptions() 将最终调用第二个，实际上是 SetFileTypes()。他们有不同的论点，当实现获得垃圾参数并且堆栈变得不平衡时，这将以一种令人讨厌的方式进行。

您可以省略尾部的任何声明。另请注意，当您不调用方法时，方法的实际声明并不重要。这使您可以撒谎并避免必须声明其参数类型。请确保该方法显然不会实际工作，将其命名为 void DontCallMe2()。

请注意，这些接口(interface)已经包含在 Windows API 代码包以及 .NET 4.0 版本的 Microsoft.Win32.OpenFileDialog 和 .NET 3.5 版本的 System.Windows.Forms.OpenFileDialog 中