[DllImport(“MyDLL.dll ")]
public static extern int mySum (int a,int b);
}

[DllImport(“MyDLL.dll ")]
public static extern int mySum (int a,int b);
代码中DllImport关键字作用是告诉编译器入口点在哪里，并将打包函数捆绑在这个类中
在调用的时候
在类中的时候 直接　 mySum(a,b);就可以了
在其他类中调用: XXXX. mySum(a,b);

[DllImport(“MyDLL.dll”)]在申明的时候还可以添加几个属性
[DllImport(“MyDLL.dll ", EntryPoint= " mySum ",CharSet=CharSet.Auto,CallingConvention=CallingConvention.StdCall)
]
EntryPoint: 指定要调用的 DLL 入口点。默认入口点名称是托管方法的名称 。
CharSet: 控制名称重整和封送 String 参数的方式 (默认是UNICODE)
CallingConvention指示入口点的函数调用约定(默认WINAPI)(上次报告讲过的）
SetLastError 指示被调用方在从属性化方法返回之前是否调用 SetLastError Win32 API 函数 (C#中默认false )

int 类型
[DllImport(“MyDLL.dll ")]
//返回个int 类型
public static extern int mySum (int a1,int b1);
//DLL中申明
extern “C” __declspec(dllexport) int WINAPI mySum(int a2,int b2)
{
//a2 b2不能改变a1 b1
//a2=..
//b2=...
return a+b;
}

//参数传递int 类型
public static extern int mySum (ref int a1,ref int b1);
//DLL中申明
extern “C” __declspec(dllexport) int WINAPI mySum(int *a2,int *b2)
{
//可以改变 a1, b1
*a2=...
*b2=...
return a+b;
}

DLL 需传入char *类型
[DllImport(“MyDLL.dll ")]
//传入值
public static extern int mySum (string astr1,string bstr1);
//DLL中申明
extern “C” __declspec(dllexport) int WINAPI mySum(char * astr2,char * bstr2)
{
//改变astr2 bstr 2 ，astr1 bstr1不会被改变
return a+b;
}

DLL 需传出char *类型
[DllImport(“MyDLL.dll ")]
// 传出值
public static extern int mySum (StringBuilder abuf, StringBuilder bbuf );
//DLL中申明
extern “C” __declspec(dllexport) int WINAPI mySum(char * astr,char * bstr)
{
//传出char *　改变astr　bstr --> abuf, bbuf可以被改变
return a+b;
}

DLL 回调函数

BOOL EnumWindows(WNDENUMPROC lpEnumFunc, LPARAM lParam)

using System;
using System.Runtime.InteropServices;
public delegate bool CallBack(int hwnd, int lParam); //定义委托函数类型
public class EnumReportApp
{
[DllImport( "user32 ")]
public static extern int EnumWindows(CallBack x, int y);
public static void Main() {
CallBack myCallBack = new CallBack(EnumReportApp.Report); EnumWindows(myCallBack, 0);
}
public static bool Report(int hwnd, int lParam)
{
Console.Write( "Window handle is ");
Console.WriteLine(hwnd); return true;
}
}

DLL 传递结构
BOOL PtInRect(const RECT *lprc, POINT pt);

using System.Runtime.InteropServices;
[StructLayout(LayoutKind.Sequential)]
public struct Point {
public int x;
public int y;
}
[StructLayout(LayoutKind.Explicit)]
public struct Rect
{
[FieldOffset(0)] public int left;
[FieldOffset(4)] public int top;
[FieldOffset(8)] public int right;
[FieldOffset(12)] public int bottom;
}
Class XXXX {
[DllImport( "User32.dll ")]
public static extern bool PtInRect(ref Rect r, Point p);
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace ClientControl
{
public partial class MainForm : Form
{
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_InitSystem();//初始化
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_ExitSystem();//退出
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_StartRecvBMP();//开始压缩图像
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_StopRecvBMP();//停止压缩图像
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_CheckNetChannel(int iAllowBandWidth); //网络信道检测
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_RegDataArriveEventHandler(TXYS_DataArriveHandler_t fHandlerFunc); //注册数据到来
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_RegReqTimeEventHandler(TXYS_RequestTimeHandler_t fHandlerFunc); //注册时间
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_RegWarnEventHandler(TXYS_WarnHandler_t fHandlerFunc); //注册警告
[DllImport( "bmpcodec.dll ")]
static extern int TXYS_RegStateNotifyEventHandler(TXYS_StateNotifyHandler_t fHandlerFunc);//注册状态

// 函数指针类型
public delegate int TXYS_DataArriveHandler_t(long iImageFrameNo, int iPackNo, int iDataSize, char[] ucData);
public delegate int TXYS_RequestTimeHandler_t();
public delegate int TXYS_WarnHandler_t(int iFaultNo, int iWarnType);
public delegate int TXYS_StateNotifyHandler_t(long lStartTime, long lEndTime,
long lMinDelayTime, long lMaxDelayTime, long lMeanDelayTime,
int iMaxLostFarmeNum, int iTotalLostFrameNum);
private delegate void UpdateDelegate(string str);
//委托操作函数
private void UpdateText(string str)
{
datalabel.Text=str;
}
TXYS_DataArriveHandler_t dataArrive;//=new TXYS_DataArriveHandler_t(
//回调函数
public int fDataArriveHandler(long iImageFrameNo, int iPackNo, int iDataSize, char[] ucData)
{
　UpdateDelegate eh = new UpdateDelegate(UpdateText);
this.datalabel.Invoke(eh, new object[] {iImageFrameNo + " "+iPackNo+ "帧数据到来 " });
datalabel.Text = " " + iImageFrameNo + "帧数据到来 ";

return 0;
}
public MainForm()
{
InitializeComponent();
TXYS_InitSystem();
dataArrive = new TXYS_DataArriveHandler_t(this.fDataArriveHandler);
TXYS_RegDataArriveEventHandler(dataArrive);//注册回调函数
}
~MainForm()
{

//TXYS_ExitSystem();
}

private void MainForm_Load(object sender, EventArgs e)
{

}
//启动图像传输
private void ButtonStart_Click(object sender, EventArgs e)
{
TXYS_StartRecvBMP();
}

private void MainForm_FormClosed(object sender, FormClosedEventArgs e)
{
TXYS_ExitSystem();
}

private void buttonStop_Click(object sender, EventArgs e)
{
TXYS_StopRecvBMP();
}
}
}