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();
}
}
}
