[置顶]在C#中SendMessage和PostMessage的参数传递

用 PostMessage、SendNotifyMessage、SendMessageCallback 等异步函数发送系统消息时，参数里不可以使用指针，因为发送者并不等待消息的处理就返回，接受者还没处理指针就已经被释放了。

5、在 Windows 2000/XP 里，每个消息队列最多只能存放 10,000 个 Post
的消息，超过的还没被处理的将不会被处理，直接丢掉。这个值可以改得更大：[HKEY_LOCAL_MACHINE/SOFTWARE/
Microsoft/Windows NT/CurrentVersion/Windows] USERPostMessageLimit，最小可以是
4000。

PostMessage只负责将消息放到消息队列中，不确定何时及是否处理

SendMessage要等到受到消息处理的返回码（DWord类型）后才继续

PostMessage执行后马上返回

SendMessage必须等到消息被处理后才会返回。

下面通过一个小例子来说明下这2个方法进行参数传递的不同点：

//Win32 API 类

using System;

using System.Runtime.InteropServices;

namespace TestHwnd

{

public class Win32API

{

[DllImport("User32.dll", EntryPoint = "FindWindow")]

public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

[DllImport("User32.dll", EntryPoint = "FindWindowEx")]

public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpClassName, string lpWindowName);

/// <summary>

/// 自定义的结构

/// </summary>

public struct My_lParam

{

public int i;

public string s;

}

/// <summary>

/// 使用COPYDATASTRUCT来传递字符串

/// </summary>

[StructLayout(LayoutKind.Sequential)]

public struct COPYDATASTRUCT

{

public IntPtr dwData;

public int cbData;

[MarshalAs(UnmanagedType.LPStr)]

public string lpData;

}

//消息发送API

[DllImport("User32.dll", EntryPoint = "SendMessage")]

public static extern int SendMessage(

IntPtr hWnd, // 信息发往的窗口的句柄

int Msg, // 消息ID

int wParam, // 参数1

int lParam //参数2

);

//消息发送API

[DllImport("User32.dll", EntryPoint = "SendMessage")]

public static extern int SendMessage(

IntPtr hWnd, // 信息发往的窗口的句柄

int Msg, // 消息ID

int wParam, // 参数1

ref My_lParam lParam //参数2

);

//消息发送API

[DllImport("User32.dll", EntryPoint = "SendMessage")]

public static extern int SendMessage(

IntPtr hWnd, // 信息发往的窗口的句柄

int Msg, // 消息ID

int wParam, // 参数1

ref COPYDATASTRUCT lParam //参数2

);

//消息发送API

[DllImport("User32.dll", EntryPoint = "PostMessage")]

public static extern int PostMessage(

IntPtr hWnd, // 信息发往的窗口的句柄

int Msg, // 消息ID

int wParam, // 参数1

int lParam // 参数2

);

//消息发送API

[DllImport("User32.dll", EntryPoint = "PostMessage")]

public static extern int PostMessage(

IntPtr hWnd, // 信息发往的窗口的句柄

int Msg, // 消息ID

int wParam, // 参数1

ref My_lParam lParam //参数2

);

//异步消息发送API

[DllImport("User32.dll", EntryPoint = "PostMessage")]

public static extern int PostMessage(

IntPtr hWnd, // 信息发往的窗口的句柄

int Msg, // 消息ID

int wParam, // 参数1

ref COPYDATASTRUCT lParam // 参数2

);

}

}

//主窗体，发送消息

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

using System.Runtime.InteropServices;

namespace TestHwnd

{

public partial class Main : Form

{

public IntPtr hwndTest;

public int IwndTest;

public IntPtr hwndfrmTest;

public Main()

{

InitializeComponent();

}

private void button1_Click(object sender, EventArgs e)

{

Test test = new Test();

test.Show(this);

}

private void timer1_Tick(object sender, EventArgs e)

{

string strTest = "25425";

Win32API.COPYDATASTRUCT cds;

cds.dwData = (IntPtr)100;

cds.lpData = strTest;

byte[] sarr = System.Text.Encoding.UTF8.GetBytes(strTest);

int len = sarr.Length;

cds.cbData = len + 1;

Win32API.My_lParam lp=new Win32API.My_lParam();

lp.i=3;

lp.s="test";

if(hwndTest!=(IntPtr)0)

{

if (DateTime.Now.Second % 2 == 0)

{

Win32API.SendMessage(hwndTest, 0x60, 1, 3);//传递2个整型参数成功

}

if(DateTime.Now.Second % 3 == 0)

{

Win32API.SendMessage(hwndTest, 0x61, 5, ref lp);//传递整型参数和结构类型成功，这个方法加以改变后可以传递对象

}

if(DateTime.Now.Second % 5 == 0)

{

Win32API.SendMessage(hwndTest, 0x62, 5, ref cds);//传递整型参数和不定长的字符串成功

}

if(DateTime.Now.Second % 7 == 0)

{

Win32API.PostMessage(hwndTest, 0x63, 5, 6);//传递2个整型参数成功

}

if(DateTime.Now.Second % 9 == 0)

{

Win32API.PostMessage(hwndTest, 0x64, 3, ref lp);//传递整型参数成功，但是传递参数lp失败，3可以传递成功。

}

if(DateTime.Now.Second % 11 == 0)

{

Win32API.PostMessage(hwndTest, 0x65, 3, ref cds);//传递整型参数成功，传递参数cds失败，3可以传递成功。

}

}

}

}

}

//子窗体接收消息以及参数

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

using System.Runtime.InteropServices;

namespace TestHwnd

{

public partial class Test : Form

{

Main main;

public Test()

{

InitializeComponent();

}

private void Test_Load(object sender, EventArgs e)

{

main = this.Owner as Main;

main.hwndTest = this.Handle;

}

///重写窗体的消息处理函数DefWndProc，从中加入自己定义消息的检测的处理入口

protected override void DefWndProc(ref Message
m)

{

switch (m.Msg)

{

//接收自定义消息MYMESSAGE，并显示其参数

case 0x60:

{

label1.Text = DateTime.Now.ToString() + "-" + m.WParam.ToInt32().ToString() + "-" + m.LParam.ToInt32().ToString();

}

break;

case 0x61:

{

Win32API.My_lParam ml = new Win32API.My_lParam();

Type t = ml.GetType();

ml = (Win32API.My_lParam)m.GetLParam(t);

label2.Text = DateTime.Now.ToString() + "-" + m.WParam.ToInt32().ToString() + "-" + ml.i.ToString()+":"+ml.s;

}

break;

case 0x62:

{

Win32API.COPYDATASTRUCT mystr = new Win32API.COPYDATASTRUCT();

Type mytype = mystr.GetType();

mystr = (Win32API.COPYDATASTRUCT)m.GetLParam(mytype);

string str2 = mystr.lpData;

label3.Text = DateTime.Now.ToString() + "-" + m.WParam.ToInt32().ToString() + "-" + str2;

}

break;

case 0x63:

{

label4.Text = DateTime.Now.ToString() + "-" + m.WParam.ToInt32().ToString() + "-" + m.LParam.ToInt32().ToString();

}

break;

case 0x64:

{

Win32API.My_lParam ml = new Win32API.My_lParam();

Type t = ml.GetType();

ml = (Win32API.My_lParam)m.GetLParam(t);

label5.Text = DateTime.Now.ToString() + "-" + m.WParam.ToInt32().ToString() + "-" + ml.i.ToString()+":"+ml.s;

}

break;

case 0x65:

{

Win32API.COPYDATASTRUCT mystr = new Win32API.COPYDATASTRUCT();

Type mytype = mystr.GetType();

mystr = (Win32API.COPYDATASTRUCT)m.GetLParam(mytype);

string str2 = mystr.lpData;

label6.Text = DateTime.Now.ToString() + "-" + m.WParam.ToInt32().ToString() + "-" + str2;

}

break;

default:

base.DefWndProc(ref m);

break;

}

}

private void button1_Click(object sender, EventArgs e)

{

main.hwndTest = (IntPtr) (0);

this.Close();

}

}

}