DayOf1440/DayOf1440/Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace DayOf1440
{
    static class Program
    {
        public static List<Form> formList = new List<Form>();

        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new MainForm());
        }

        /// <summary>
        /// new a Form object
        /// </summary>
        /// <param name="type"></param>
        /// <returns></returns>
        internal static Form getInstance(Type type)
        {
            Form currentForm = null;
            foreach (Form formItem in formList)
            {
                if (formItem.GetType() == type)
                {
                    currentForm = formItem;
                    currentForm.Activate();
                    break;
                }

            }
            if (currentForm == null)
            {
                object obj = Activator.CreateInstance(type);
                if (obj is Form)
                {
                    currentForm = obj as Form;
                    currentForm.Show();
                }
            }
            return currentForm;
        }

    }
}