同时只有一个窗体实例，再次打开激活已打开窗体的范例

新建一个windows application，吧program.cs文件替换为以下内容即可。

using System; using System.Diagnostics; using System.Runtime.InteropServices; using System.Windows.Forms; namespace CSharpWin08 { static class Program { [DllImport("user32.dll", EntryPoint = "SetForegroundWindow")] public static extern int SetForegroundWindow(IntPtr hwnd); [DllImport("user32.dll", EntryPoint = "SendMessage")] public static extern int SendMessage(IntPtr hwnd, int wMsg, int wParam, int lParam); public const int WM_SYSCOMMAND = 0x112; public const int SC_RESTORE = 0xF120; /// <summary> /// 应用程序的主入口点。 /// </summary> [STAThread] static void Main() { Process cur = Process.GetCurrentProcess(); foreach (Process p in Process.GetProcesses()) { if (p.Id == cur.Id) continue; if (p.ProcessName == cur.ProcessName) { SetForegroundWindow(p.MainWindowHandle); SendMessage(p.MainWindowHandle, WM_SYSCOMMAND, SC_RESTORE, 0); return; } } Application.Run(new Form2()); } } }