[原创]C#引用C++编译的dll

一、DllImportAttribute

1、属性介绍

 using System;
 using System.Reflection;
 using System.Security;

 namespace System.Runtime.InteropServices
 {
     // Summary:
     //     Indicates that the attributed method is exposed by an unmanaged dynamic-link
     //     library (DLL) as a static entry point.
     [AttributeUsage(AttributeTargets.Method, Inherited = false)]
     [ComVisible(true)]
     public sealed class DllImportAttribute : Attribute
     {
         // Summary:
         //     Enables or disables best-fit mapping behavior when converting Unicode characters
         //     to ANSI characters.
         public bool BestFitMapping;
         //
         // Summary:
         //     Indicates the calling convention of an entry point.
         public CallingConvention CallingConvention;
         //
         // Summary:
         //     Indicates how to marshal string parameters to the method and controls name
         //     mangling.
         public CharSet CharSet;
         //
         // Summary:
         //     Indicates the name or ordinal of the DLL entry point to be called.
         public string EntryPoint;
         //
         // Summary:
         //     Controls whether the System.Runtime.InteropServices.DllImportAttribute.CharSet
         //     field causes the common language runtime to search an unmanaged DLL for entry-point
         //     names other than the one specified.
         public bool ExactSpelling;
         //
         // Summary:
         //     Indicates whether unmanaged methods that have HRESULT or retval return values
         //     are directly translated or whether HRESULT or retval return values are automatically
         //     converted to exceptions.
         public bool PreserveSig;
         //
         // Summary:
         //     Indicates whether the callee calls the SetLastError Win32 API function before
         //     returning from the attributed method.
         public bool SetLastError;
         //
         // Summary:
         //     Enables or disables the throwing of an exception on an unmappable Unicode
         //     character that is converted to an ANSI "?" character.
         public bool ThrowOnUnmappableChar;

         // Summary:
         //     Initializes a new instance of the System.Runtime.InteropServices.DllImportAttribute
         //     class with the name of the DLL containing the method to import.
         //
         // Parameters:
         //   dllName:
         //     The name of the DLL that contains the unmanaged method. This can include
         //     an assembly display name, if the DLL is included in an assembly.
         public DllImportAttribute(string dllName);

         // Summary:
         //     Gets the name of the DLL file that contains the entry point.
         //
         // Returns:
         //     The name of the DLL file that contains the entry point.
         public string Value { get; }
     }
 }

2、举例

 class BLApi
 {
     [DllImport(@"xx.dll", EntryPoint = "TWelcomeFace_Init", ExactSpelling = false, CallingConvention = CallingConvention.Cdecl)]
     public extern static Int32 TWelcomeFace_Init(string namingService, string localhost, string dvsService, string matchService);
 }

3、引入依赖dll

将依赖dll添加到解决方案中，与主dll放在相同目录下（重要），然后设置dll的属性CopyToOutputDirectory= CopyAlways，编译器就会自动找到了。

二、应用LoadLibrary

1、封装基础类

 public class DllInvoke
     {
         [DllImport("kernel32.dll")]
         private extern static IntPtr LoadLibrary(String path);
         [DllImport("kernel32.dll")]
         private extern static IntPtr GetProcAddress(IntPtr lib, String funcName);
         [DllImport("kernel32.dll")]
         private extern static bool FreeLibrary(IntPtr lib);
         [DllImport("kernel32.dll")]
         private extern static int GetLastError();
         private IntPtr hLib;
         public DllInvoke(String dllPath, List<string> DependentDllPaths = null)
         {
             if(DependentDllPaths != null)
             {
                 foreach (string dllName in DependentDllPaths)
                 {
                     IntPtr loadAuxiliary = LoadLibrary(dllName);
                     if (loadAuxiliary == IntPtr.Zero)
                     {
                         throw new Exception(dllName + "加载失败！");
                     }
                 }
             }
             hLib = LoadLibrary(dllPath);
         }
         ~DllInvoke()
         {
             FreeLibrary(hLib);
         }

         public Delegate Invoke(String APIName, Type t)
         {
             IntPtr api = GetProcAddress(hLib, APIName);
             var s = Marshal.GetDelegateForFunctionPointer(api, t);
             return (Delegate)s;
         }
     }

LoadLibrary引用的dll相关的依赖dll必须被手动引用进来，否则会报错。

2、举例

 [UnmanagedFunctionPointer(CallingConvention.Cdecl, CharSet = CharSet.Ansi, SetLastError = true)]
     delegate Int32 TWelcomeFace_Init(string Naming_Service, string Locale_Host, string DVS_Service, string Match_Service);

  class BLApi
     {
         private static DllInvoke _dll = new DllInvoke(@"xx.dll");

         public static Int32 TWelcomeFace_Init(string namingService, string localhost, string dvsService, string matchService)
         {
             try
             {
                 TWelcomeFace_Init dele = (TWelcomeFace_Init)_dll.Invoke("TWelcomeFace_Init", typeof(TWelcomeFace_Init));
                 Int32 result = dele(namingService, localhost, dvsService, matchService);

                 return result;
             }
             catch (Exception ex)
             {
                 throw ex;
             }
         }
     }