//调用方式 

var frm = new MyForm().Instance();

public static class ExFrm

{

    static Dictionary<string, Form> forms = new Dictionary<string, Form>();

    /// <summary>

    /// 单例模式

    /// </summary>

    /// <typeparam name="T"></typeparam>

    /// <param name="frm"></param>

    /// <returns></returns>

    public static T Instance<T>(this T frm) where T : Form

    {

        frm.FormClosed += (s, e) => frm.Dispose();

        if (forms.ContainsKey(frm.Name) == false)

        {

            forms.Add(frm.Name, frm);

            return frm;

        }

        if (forms[frm.Name].IsDisposed)

        {

            forms[frm.Name] = frm;

            return frm;

        }

        frm.Close();

        return forms[frm.Name] as T;

    }

}