winform 检查窗口是否已打开

    using System;  
    using System.Collections.Generic;  
    using System.ComponentModel;  
    using System.Data;  
    using System.Drawing;  
    using System.Text;  
    using System.Windows.Forms;  
    using System.Runtime.InteropServices;  
    namespace WindowsForm  
    {  
        publicpartialclass Form1 : Form  
         {  
            public Form1()  
             {  
                 InitializeComponent();  
             }  
            ///<summary>  
            /// 获取窗体句柄  
            ///</summary>  
            ///<param name="lpClassName"></param>  
            ///<param name="lpWindowName">窗体名称</param>  
            ///<returns>IntPtr 句柄</returns>  
             [DllImport("User32.dll")]  
            privatestaticextern IntPtr FindWindow(String lpClassName, String lpWindowName);  
             [DllImport("User32.dll")]  
            publicstaticexternint IsWindow(IntPtr hWnd);  
            ///<summary>  
            ///   该函数将创建指定窗口的线程设置到前台，并且激活该窗口。键盘输入转向该窗口，并为用户改各种可视的记号。  
            ///   系统给创建前台窗口的线程分配的权限稍高于其他线程。  
            ///</summary>  
            ///<param name="hWnd">将被激活并被调入前台的窗口句柄</param>  
            ///<returns>如果窗口设入了前台，返回值为非零；如果窗口未被设入前台，返回值为零</returns>  
             [DllImport("User32.dll")]  
            privatestaticexternbool SetForegroundWindow(IntPtr hWnd);  
            privatevoid button1_Click(object sender, EventArgs e)  
             {  
                 IntPtr handle = FindWindow(null, "Form2");  
                if (IsWindow(handle) >0)  
                 {  
                     SetForegroundWindow(handle);  
                 }  
                else  
                 {  
                     Form2 f =new Form2();  
                     f.Show();  
                 }  
             }  
         }  
    }