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[ASP.net教程][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 = "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();     }   }   }