[C#.net]PostMessage與SendMessage的區別，
用 PostMessage、SendNotifyMessage、SendMessageCallback 等異步函數發送系統消息時，參數裡不可以使用指針，因為發送者並不等待消息的處理就返回，接受者還沒處理指針就已經被釋放了。
5、在 Windows 2000/XP 裡，每個消息隊列最多只能存放 10,000 個 Post
的消息，超過的還沒被處理的將不會被處理，直接丟掉。這個值可以改得更大：[HKEY_LOCAL_MACHINE/SOFTWARE/
Microsoft/Windows NT/CurrentVersion/Windows] USERPostMessageLimit，最小可以是
4000。
PostMessage只負責將消息放到消息隊列中，不確定何時及是否處理
SendMessage要等到受到消息處理的返回碼（DWord類型）後才繼續
PostMessage執行後馬上返回
SendMessage必須等到消息被處理後才會返回。
下面通過一個小例子來說明下這2個方法進行參數傳遞的不同點：
//Win32 API 類
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>
/// 自定義的結構
/// </summary>
public struct My_lParam
{
public int i;
public string s;
}
/// <summary>
/// 使用COPYDATASTRUCT來傳遞字符串
/// </summary>
[StructLayout(LayoutKind.Sequential)]
public struct COPYDATASTRUCT
{
public IntPtr dwData;
public int cbData;
[MarshalAs(UnmanagedType.LPStr)]
public string lpData;
}
//消息發送API
[DllImport("User32.dll", EntryPoint = "SendMessage")]
public static extern int SendMessage(
IntPtr hWnd, // 信息發往的窗口的句柄
int Msg, // 消息ID
int wParam, // 參數1
int lParam //參數2
);
//消息發送API
[DllImport("User32.dll", EntryPoint = "SendMessage")]
public static extern int SendMessage(
IntPtr hWnd, // 信息發往的窗口的句柄
int Msg, // 消息ID
int wParam, // 參數1
ref My_lParam lParam //參數2
);
//消息發送API
[DllImport("User32.dll", EntryPoint = "SendMessage")]
public static extern int SendMessage(
IntPtr hWnd, // 信息發往的窗口的句柄
int Msg, // 消息ID
int wParam, // 參數1
ref COPYDATASTRUCT lParam //參數2
);
//消息發送API
[DllImport("User32.dll", EntryPoint = "PostMessage")]
public static extern int PostMessage(
IntPtr hWnd, // 信息發往的窗口的句柄
int Msg, // 消息ID
int wParam, // 參數1
int lParam // 參數2
);
//消息發送API
[DllImport("User32.dll", EntryPoint = "PostMessage")]
public static extern int PostMessage(
IntPtr hWnd, // 信息發往的窗口的句柄
int Msg, // 消息ID
int wParam, // 參數1
ref My_lParam lParam //參數2
);
//異步消息發送API
[DllImport("User32.dll", EntryPoint = "PostMessage")]
public static extern int PostMessage(
IntPtr hWnd, // 信息發往的窗口的句柄
int Msg, // 消息ID
int wParam, // 參數1
ref COPYDATASTRUCT lParam // 參數2
);
}
}
//主窗體，發送消息
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);//傳遞2個整型參數成功
}
if(DateTime.Now.Second % 3 == 0)
{
Win32API.SendMessage(hwndTest, 0x61, 5, ref lp);//傳遞整型參數和結構類型成功，這個方法加以改變後可以傳遞對象
}
if(DateTime.Now.Second % 5 == 0)
{
Win32API.SendMessage(hwndTest, 0x62, 5, ref cds);//傳遞整型參數和不定長的字符串成功
}
if(DateTime.Now.Second % 7 == 0)
{
Win32API.PostMessage(hwndTest, 0x63, 5, 6);//傳遞2個整型參數成功
}
if(DateTime.Now.Second % 9 == 0)
{
Win32API.PostMessage(hwndTest, 0x64, 3, ref lp);//傳遞整型參數成功，但是傳遞參數lp失敗，3可以傳遞成功。
}
if(DateTime.Now.Second % 11 == 0)
{
Win32API.PostMessage(hwndTest, 0x65, 3, ref cds);//傳遞整型參數成功，傳遞參數cds失敗，3可以傳遞成功。
}
}
}
}
}
//子窗體接收消息以及參數
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;
}
///重寫窗體的消息處理函數DefWndProc，從中加入自己定義消息的檢測的處理入口
protected override void DefWndProc(ref Message m)
{
switch (m.Msg)
{
//接收自定義消息MYMESSAGE，並顯示其參數
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();
}
}
}
