C#调用非托管dll的两种方式详解

library testDLL;

uses
  SysUtils,
  Dialogs,
  Classes;

{$R *.res}

function MyFunction(param1: Integer): Integer; stdcall;
begin
  Result := param1 + 1;
end;

exports
  MyFunction;

begin
end.

[DllImport("testDLL.dll")]
static extern int MyFunction(int a);

int i = MyFunction(123);

// 辅助方法：加载DLL
[DllImport("kernel32.dll", SetLastError = true)]
static extern IntPtr LoadLibrary(string lpFileName);

// 辅助方法：卸载DLL
[DllImport("kernel32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool FreeLibrary(IntPtr hModule);

// 获取方法指针
[DllImport("kernel32.dll", SetLastError = true)]
private static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);

public delegate int MyFunctionDelphiDelegate(int param1);

void run()
{
    // 加载DLL
    IntPtr dllHandle = LoadLibrary("testDLL.dll");
    if (dllHandle == IntPtr.Zero)
    {
        var err = Marshal.GetHRForLastWin32Error();
    }

    // 获取方法指针
    IntPtr functionPointer = GetProcAddress(dllHandle, "MyFunction");

    MyFunctionDelphiDelegate my = (MyFunctionDelphiDelegate)Marshal.GetDelegateForFunctionPointer(functionPointer, typeof(MyFunctionDelphiDelegate));
    // 调用方法
    int i = my(1);

    // 释放DLL
    FreeLibrary(dllHandle);
}