sendmessage 用法

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();
        }

        

    }

    
}