WinForm singleton form usage example

using System;
using ;
using ;
using ;
namespace Common
{
  /// <summary>
  /// Singleton mode of form  /// </summary>
  /// <typeparam name="T"></typeparam>
  public class FormSingle<T> where T : Form, new()
  {
    private static T form;
    private static IList<T> list { get; set; }
    public static T GetForm(T t1)
    {
      //Check whether the form exists      if (!IsExist(t1))
      {
        CreateNewForm(t1);
      }
      return form;
    }
    /// <summary>Release the object    /// &lt;/summary&gt;
    /// &lt;param name="obj"&gt;&lt;/param&gt;
    /// &lt;param name="args"&gt;&lt;/param&gt;
    private static void Display(object obj, FormClosedEventArgs args)
    {
      form = null;
      (form);
    }
    /// <summary>Create a new form    /// &lt;/summary&gt;
    private static void CreateNewForm(T t1)
    {
      form = t1;
       += new FormClosedEventHandler(Display);//Subscribe to the form's closing event and release the object    }
    /// &lt;summary&gt;
    /// Whether this form exists    /// &lt;/summary&gt;
    /// &lt;param name="T1"&gt;&lt;/param&gt;
    /// &lt;returns&gt;&lt;/returns&gt;
    private static bool IsExist(T T1)
    {
      if (list == null)
      {
        list=new List&lt;T&gt;();
        (T1);
        return false;
      }
      //If the text of the form is the same, it is considered to be the same form      foreach (var t in list)
      {
        if ( == )
          return true;
      }
      (T1);
      return false;
    }
  }
}

 customer = <>.GetForm(new ());
 = this;//Mdi Form = ;//maximize();
();

 customer = <>.GetForm(new (customerid));
 = this;
 = ;
();
();