[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;
            }
        }
    }