同时只有一个窗体实例，再次打开激活已打开窗体的范例

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1. using System;  
2. using System.Diagnostics;  
3. using System.Runtime.InteropServices;  
4. using System.Windows.Forms;  
5.   
6. namespace CSharpWin08  
7. {  
8.     static class Program  
9.     {  
10.         [DllImport("user32.dll", EntryPoint = "SetForegroundWindow")]  
11.         public static extern int SetForegroundWindow(IntPtr hwnd);  
12.         [DllImport("user32.dll", EntryPoint = "SendMessage")]  
13.         public static extern int SendMessage(IntPtr hwnd, int wMsg, int wParam, int lParam);  
14.         public const int WM_SYSCOMMAND = 0x112;  
15.         public const int SC_RESTORE = 0xF120;  
16.         /// <summary>  
17.         /// 应用程序的主入口点。  
18.         /// </summary>  
19.         [STAThread]  
20.         static void Main()  
21.         {  
22.             Process cur = Process.GetCurrentProcess();  
23.             foreach (Process p in Process.GetProcesses())  
24.             {  
25.                 if (p.Id == cur.Id) continue;  
26.                 if (p.ProcessName == cur.ProcessName)  
27.                 {  
28.                     SetForegroundWindow(p.MainWindowHandle);  
29.                     SendMessage(p.MainWindowHandle, WM_SYSCOMMAND, SC_RESTORE, 0);  
30.                     return;  
31.                 }  
32.             }  
33.             Application.Run(new Form2());  
34.         }  
35.     }  
36. }