C＃面板属性更改时内存泄漏

Question

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace OcppDummyClient
{
    public partial class Form1 : Form
    {
        public string[] messages = new string[]
        {
           "Authorize",
           "BootNoficiation"
        };

        public Panel A;
        public Panel B;

        public Form1()
        {
            InitializeComponent();
            InitializeForm();

            A = new Panel()
            {
                Width = this.flowLayoutPanel1.Width,
                Height = this.flowLayoutPanel1.Height,
                BackColor = Color.Black
            };

            A.Controls.Add(new Button()
            {
                Text = "Button"
            });

            B = new Panel()
            {
                Width = this.flowLayoutPanel1.Width,
                Height = this.flowLayoutPanel1.Height,
                BackColor = Color.Blue
            };

            B.Controls.Add(new Button()
            {
                Text = "Button2"
            });

            this.flowLayoutPanel1.Controls.Add(A);
            this.flowLayoutPanel1.Controls.Add(B);
        }

        public void InitializeForm()
        {
            this.comboBox1.Items.AddRange(messages);
        }

        private void comboBox1_SelectedValueChanged(object sender, EventArgs e)
        {
            string SelectedValue = this.comboBox1.Text.ToString();

            switch(SelectedValue)
            {
                case "Authorize":
                {
                    A.Visible = true;
                    B.Visible = false;
                    break;
                }

                case "BootNoficiation":
                {
                    A.Visible = false;
                    B.Visible = true;
                    break;
                }

                default:
                {
                    break;
                }
            }
        }
    }
}

That is my whole code and I want to know why memory leak is occurred when I changed combobox with event handler(comboBox1_SelectedValueChanged). I thought memory leak not happened because I already created panel and just changed panel property(visible).

Answer 1

A memory increase does not indicate a memory leak in managed memory. The memory will only be reclaimed upon garbage collection. Until then memory usage will increase. A memory "leak" happens when an object that should be garbage collected is not really dead (because there are some unintended active references to it).

Having said that, you should still be careful with WinForms controls. Because they actually wrap a native Windows control, they claim a control handle from Windows. This handle is released when calling the Dispose method of the control. This can (and in most cases will) happen during garbage collection, but until then the handle is not returned to windows (and there is no 100% guarantee of diposal during garbage collection). To avoid a resource leak from too many open Windows handles, you should dispose WinForms controls as soon as you don't need them anymore.

Disposing a Control will also dispose all child controls that are in its Controls collection. Since you add both panels to that collection, you are probably safe there, too.