[C# Windows Form] 섬네일 현재 영역만 그려주기 (Scroll, Thumbnail)

현재 영역에 대해서만 그려주기! (4개만 보이는 상태)

 

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        private const int buttonOffset = 10;

        private List<Button> buttonList = new List<Button>();
        private List<Control> focusedList = new List<Control>();
        private int scrollPosition;

        public Form1()
        {
            InitializeComponent();

            panel1.AutoScroll = true; //스크롤 활성화

            //스크롤 이벤트
            this.panel1.Resize += new System.EventHandler(this.panel1_Resize);
            this.panel1.Scroll += new System.Windows.Forms.ScrollEventHandler(this.panel1_Scroll);
        }

        private void button_add_Click_(object sender, EventArgs e)
        {
            Button button = new Button();

            button.Text = buttonList.Count.ToString("D4");
            button.Hide();

            panel1.Controls.Add(button);
            panel1.AutoScrollMinSize = new Size(panel1.AutoScrollMinSize.Width + button.Width + buttonOffset, 0);

            buttonList.Add(button);
            UpdateThumbnail(scrollPosition);
        }

        private void UpdateThumbnail (int startPosition)
        {
            int totalWidth = 0;

            //돌면서 그려줘야 할 영역에 대해서만 그려주기!
            for (int i = 0; i < buttonList.Count; ++i)
            {
                totalWidth += buttonList[i].Width + buttonOffset;

                //처음으로 커지는 구간을 찾기! 시작 지점!
                if (totalWidth >= startPosition)
                {
                    int showPositionX = totalWidth - startPosition - buttonList[i].Width - buttonOffset;

                    List<Control> newFocusList = new List<Control>();

                    for (int j = i; j < buttonList.Count; ++j)
                    {
                        Point position = new Point(showPositionX, 0);
                        showPositionX += buttonList[j].Width + buttonOffset;

                        buttonList[j].Location = position;
                        buttonList[j].Show();

                        newFocusList.Add(buttonList[j]);

                        if (this.Width <= showPositionX)
                        {
                            break;
                        }
                    }

                    //현재 영역에 들어있지 않은 기존 항목은 제거해줍니다.
                    foreach (Control item in focusedList)
                    {
                        if (newFocusList.Contains(item) == false)
                        {
                            item.Hide();
                        }
                    }

                    //현재 항목을 갱신합니다.
                    focusedList = newFocusList;

                    break;
                }
            }
        }

        private void panel1_Scroll(object sender, ScrollEventArgs e)
        {
            scrollPosition = e.NewValue;
            Console.WriteLine("scrollPosition : " + scrollPosition);
            UpdateThumbnail(scrollPosition);
        }

        private void panel1_Resize(object sender, EventArgs e)
        {
            if (panel1.AutoScrollMinSize.Width - panel1.Width <= scrollPosition)
            {
                Console.WriteLine("*************************** 크기 변경!!!");

                scrollPosition = Math.Max(0, panel1.AutoScrollMinSize.Width - panel1.Width);
                panel1.HorizontalScroll.Value = scrollPosition;
            }

            UpdateThumbnail(scrollPosition);
        }
    }
}