public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            var f = new UserControl1() { AllowDrop = false};
            this.Controls.Add(f);
            this.Controls.Remove(f);
            GCCheck();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            var f = new UserControl1() { AllowDrop = true};
            this.Controls.Add(f);
            this.Controls.Remove(f);
            GCCheck();
        }
        private void GCCheck()
        {
            var a = GC.GetTotalMemory(false);
            var b = GC.GetTotalMemory(true);
            Console.WriteLine("GC Before=" + a + " After=" + b);
        }
    }


public partial class UserControl1 : UserControl
    {
        public UserControl1()
        {
            InitializeComponent();
        }
        ~UserControl1()
        {
            Console.WriteLine(this.GetType().Name + "は解放されました " + "{AllowDrop = " + this.AllowDrop + " }");
        }
    }