[C#.net]PostMessage与SendMessage的区别

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 = "";
Win32API.COPYDATASTRUCT cds;
cds.dwData = (IntPtr);
cds.lpData = strTest;
byte[] sarr = System.Text.Encoding.UTF8.GetBytes(strTest);
int len = sarr.Length;
cds.cbData = len + ; Win32API.My_lParam lp=new Win32API.My_lParam();
lp.i=;
lp.s="test"; if(hwndTest!=(IntPtr))
{
if (DateTime.Now.Second % == )
{
Win32API.SendMessage(hwndTest, 0x60, , );//传递2个整型参数成功
}
if(DateTime.Now.Second % == )
{
Win32API.SendMessage(hwndTest, 0x61, , 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 % == )
{
Win32API.SendMessage(hwndTest, 0x62, , ref cds);//传递整型参数和不定长的字符串成功
}
if(DateTime.Now.Second % == )
{
Win32API.PostMessage(hwndTest, 0x63, , );//传递2个整型参数成功
}
if(DateTime.Now.Second % == )
{
Win32API.PostMessage(hwndTest, 0x64, , 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 % == )
{
Win32API.PostMessage(hwndTest, 0x65, , 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) ();
this.Close();
}
}
}
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