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
usingSystem;
usingSystem.Runtime.InteropServices;
namespaceTestHwnd
{
publicclassWin32API
{
[DllImport("User32.dll",EntryPoint ="FindWindow")]
publicstaticexternIntPtrFindWindow(stringlpClassName,stringlpWindowName);
[DllImport("User32.dll",EntryPoint ="FindWindowEx")]
publicstaticexternIntPtrFindWindowEx(IntPtr hwndParent,IntPtr hwndChildAfter,stringlpClassName,stringlpWindowName);
///<summary>
///自定义的结构
///</summary>
publicstructMy_lParam
{
publicinti;
publicstrings;
}
///<summary>
///使用COPYDATASTRUCT来传递字符串
///</summary>
[StructLayout(LayoutKind.Sequential)]
publicstructCOPYDATASTRUCT
{
publicIntPtr dwData;
publicintcbData;
[MarshalAs(UnmanagedType.LPStr)]
publicstringlpData;
}
//消息发送API
[DllImport("User32.dll",EntryPoint ="SendMessage")]
publicstaticexternintSendMessage(
IntPtr hWnd,// 信息发往的窗口的句柄
intMsg,// 消息ID
intwParam,// 参数1
intlParam//参数2
);
//消息发送API
[DllImport("User32.dll",EntryPoint ="SendMessage")]
publicstaticexternintSendMessage(
IntPtr hWnd,// 信息发往的窗口的句柄
intMsg,// 消息ID
intwParam,// 参数1
refMy_lParam lParam//参数2
);
//消息发送API
[DllImport("User32.dll",EntryPoint ="SendMessage")]
publicstaticexternintSendMessage(
IntPtr hWnd,// 信息发往的窗口的句柄
intMsg,// 消息ID
intwParam,// 参数1
refCOPYDATASTRUCT lParam//参数2
);
//消息发送API
[DllImport("User32.dll",EntryPoint ="PostMessage")]
publicstaticexternintPostMessage(
IntPtr hWnd,// 信息发往的窗口的句柄
intMsg,// 消息ID
intwParam,// 参数1
intlParam// 参数2
);
//消息发送API
[DllImport("User32.dll",EntryPoint ="PostMessage")]
publicstaticexternintPostMessage(
IntPtr hWnd,// 信息发往的窗口的句柄
intMsg,// 消息ID
intwParam,// 参数1
refMy_lParam lParam//参数2
);
//异步消息发送API
[DllImport("User32.dll",EntryPoint ="PostMessage")]
publicstaticexternintPostMessage(
IntPtr hWnd,// 信息发往的窗口的句柄
intMsg,// 消息ID
intwParam,// 参数1
refCOPYDATASTRUCT lParam// 参数2
);
}
}
//主窗体，发送消息
usingSystem;
usingSystem.Collections.Generic;
usingSystem.ComponentModel;
usingSystem.Data;
usingSystem.Drawing;
usingSystem.Linq;
usingSystem.Text;
usingSystem.Windows.Forms;
usingSystem.Runtime.InteropServices;
namespaceTestHwnd
{
publicpartialclassMain : Form
{
publicIntPtr hwndTest;
publicintIwndTest;
publicIntPtr hwndfrmTest;
publicMain()
{
InitializeComponent();
}
privatevoidbutton1_Click(objectsender,EventArgs e)
{
Test test =newTest();
test.Show(this);
}
privatevoidtimer1_Tick(objectsender,EventArgs e)
{
stringstrTest ="25425";
Win32API.COPYDATASTRUCT cds;
cds.dwData =(IntPtr)100;
cds.lpData = strTest;
byte[]sarr = System.Text.Encoding.UTF8.GetBytes(strTest);
intlen = sarr.Length;
cds.cbData = len+1;
Win32API.My_lParam lp=newWin32API.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,reflp);//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,refcds);//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,reflp);//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,refcds);//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
usingSystem;usingSystem.Collections.Generic;
usingSystem.ComponentModel;
usingSystem.Data;
usingSystem.Drawing;
usingSystem.Linq;
usingSystem.Text;
usingSystem.Windows.Forms;
usingSystem.Runtime.InteropServices;
namespaceTestHwnd
{
publicpartialclassTest : Form
{
Main main;
publicTest()
{
InitializeComponent();
}
privatevoidTest_Load(objectsender,EventArgs e)
{
main =this.OwnerasMain;
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
protectedoverridevoidDefWndProc(refMessage m)
{
switch(m.Msg)
{
//接收自定义消息MYMESSAGE，并显示其参数
case0x60:
{
label1.Text = DateTime.Now.ToString()+"-"+m.WParam.ToInt32().ToString()+"-"+m.LParam.ToInt32().ToString();
}
break;
case0x61:
{
Win32API.My_lParam ml =newWin32API.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;
case0x62:
{
Win32API.COPYDATASTRUCT mystr =newWin32API.COPYDATASTRUCT();
Type mytype = mystr.GetType();
mystr =(Win32API.COPYDATASTRUCT)m.GetLParam(mytype);
stringstr2 = mystr.lpData;
label3.Text = DateTime.Now.ToString()+"-"+m.WParam.ToInt32().ToString()+"-"+str2;
}
break;
case0x63:
{
label4.Text = DateTime.Now.ToString()+"-"+m.WParam.ToInt32().ToString()+"-"+m.LParam.ToInt32().ToString();
}
break;
case0x64:
{
Win32API.My_lParam ml =newWin32API.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;
case0x65:
{
Win32API.COPYDATASTRUCT mystr =newWin32API.COPYDATASTRUCT();
Type mytype = mystr.GetType();
mystr =(Win32API.COPYDATASTRUCT)m.GetLParam(mytype);
stringstr2 = mystr.lpData;
label6.Text = DateTime.Now.ToString()+"-"+m.WParam.ToInt32().ToString()+"-"+str2;
}
break;
default:
base.DefWndProc(refm);
break;
}
}
privatevoidbutton1_Click(objectsender,EventArgs e)
{
main.hwndTest =(IntPtr)(0);
this.Close();
}
}
}