using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Windows.Forms;
 
public class C {
 
    public delegate bool WNDENUMPROC(IntPtr hwnd, uint lParam);
    [DllImport("user32.dll", SetLastError = true)]
    public static extern bool EnumWindows(WNDENUMPROC lpEnumFunc, uint lParam);
 
    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr GetParent(IntPtr hWnd);
    [DllImport("user32.dll")]
    public static extern uint GetWindowThreadProcessId(IntPtr hWnd, ref uint lpdwProcessId);
 
    [DllImport("kernel32.dll")]
    public static extern void SetLastError(uint dwErrCode);
 
 
    public static IntPtr GetProcessWnd()
    {
        IntPtr ptrWnd = IntPtr.Zero;
        uint pid = (uint)Process.GetCurrentProcess().Id;  // 当前进程 ID
 
        bool bResult = EnumWindows(new WNDENUMPROC(delegate (IntPtr hwnd, uint lParam)
        {
            uint id = 0;
 
            if (GetParent(hwnd) == IntPtr.Zero)
            {
                GetWindowThreadProcessId(hwnd, ref id);
                if (id == lParam)    // 找到进程对应的主窗口句柄
                {
                    ptrWnd = hwnd;   // 把句柄缓存起来
                    SetLastError(0);    // 设置无错误
                    return false;   // 返回 false 以终止枚举窗口
                }
            }
 
            return true;
 
        }), pid);
 
        return (!bResult && Marshal.GetLastWin32Error() == 0) ? ptrWnd : IntPtr.Zero;
    }
 
}

来源：https://blog.csdn.net/linkrules/article/details/50420797