怎样通过正在运行的Process获取窗体的实例？解决办法

怎样通过正在运行的Process获取窗体的实例？
今天在做程序的单实例运行时发现个问题(Winform)，我将程序运行后最小化到托盘，再次双击程序时弹出已运行的程序。
[code=C#]
[DllImport( "User32.dll ")]
private   static   extern   bool   ShowWindowAsync(IntPtr   hWnd,   int   cmdShow);
[DllImport( "User32.dll ")]
private   static   extern   bool   SetForegroundWindow(IntPtr   hWnd);
private   const   int   WS_SHOWNORMAL   =   1;
///   <summary>
///   程序入口
///   </summary>
[STAThread]
static   void   Main()
{
        //其他代码省略。。。
        Process   instance   =   RunningInstance();
        if   (instance   ==   null)
        {//运行程序}
        else//程序已经运行，显示已运行的程序
        {
                System.IntPtr   handler   =   instance.MainWindowHandle;
                frmDefault   frm   =   (frmDefault)Form.FromHandle(handler);//frmDefault程序主窗体，就是这句的问题
                frm.FormOpen();//主窗体中点击托盘图标显示窗体的方法
        }
}
[/code]
frmDefault   frm   =   (frmDefault)Form.FromHandle(handler);这句获取的frm是Null.
我试了下Form   frm   =   (Form)Form.FromHandle(handler);frm   还是Null

请问怎么能通过运行的Process得到窗体的实例?

[解决办法]
用API:
ShowWindow(SW_SHOWNORMAL);
[解决办法]
帮顶~~~~~~~~~
[解决办法]
搞不懂 是不是可以父子窗体来搞这个东西
[解决办法]
我以前也做过类似的功能，就是当一个.exe程序（winform应用程序）已经打开的时候，再双击图标打开的时候就提示：程序已经启动，具体实现代码如下：
[STAThread]
static void Main()
{
bool canStart;
System.Threading.Mutex mutex = new System.Threading.Mutex(false,"进程名字－不带.exe的（也就是窗体的名字），我这里是GIS_DMC",out canStart);
if (canStart)
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new GIS_DMCForm());
}
else
{
MessageBox.Show("程序已启动");
}
}
[解决办法]

C# code

[DllImport("User32.dll ", EntryPoint = "FindWindow")]        private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);        [DllImport("user32.dll", EntryPoint = "ShowWindow", CharSet = CharSet.Auto)]        public static extern int ShowWindow(IntPtr hwnd, int nCmdShow);        [DllImport("user32.dll", EntryPoint = "SetForegroundWindow")]        public static extern bool SetF(IntPtr hWnd);        [STAThread]        static void Main()        {            Application.EnableVisualStyles();            Application.SetCompatibleTextRenderingDefault(false);            Process current = RunningInstance();            if (current != null)            {                IntPtr handle = FindWindow(null, "Form1");                ShowWindow(handle, 1);                SetF(handle);            }            else            {                Application.EnableVisualStyles();                Application.SetCompatibleTextRenderingDefault(false);                Application.Run(new Form1());            }        }        public static Process RunningInstance()        {            Process current = Process.GetCurrentProcess();            Process[] processes = Process.GetProcessesByName(current.ProcessName);            foreach (Process process in processes)            {                if (process.Id != current.Id)                {                    if (Assembly.GetExecutingAssembly().Location.Replace("/", "\\") == current.MainModule.FileName)                    {                        return process;                    }                }            }            return null;        } 
 
[解决办法]
我是来学习的，路过帮顶
[解决办法]
C# code
[System.Runtime.InteropServices.DllImport("user32.dll")]     private   static   extern   IntPtr   FindWindow(string   strclassName,   string   strWindowName);         [System.Runtime.InteropServices.DllImport("user32.dll")]     private   static   extern   bool   OpenIcon(IntPtr   hWnd);         [System.Runtime.InteropServices.DllImport("user32.dll")]     private   static   extern   bool   IsIconic(IntPtr   hWnd);         [System.Runtime.InteropServices.DllImport("user32.dll")]     private   static   extern   int   SetForegroundWindow(IntPtr   hWnd);         void   FindAndOpenWindow(string   Title)     {     IntPtr   hWnd   = (IntPtr )  FindWindow(null,   Title);     if   (hWnd   !=   IntPtr.Zero)     {     bool   isIcon   =   IsIconic(hWnd);     if   (   !isIcon   )     {     SetForegroundWindow(hWnd);     }     else     {     OpenIcon(hWnd);     }     }     }
[解决办法]
看了这么多 API，再回过头来看看楼主的需求，最适合的应该是Singleton 模式了，
使用这个，就没有楼主说的那些 api 烦劳