C#创建自定义控件的示例

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
 
namespace WindowsFormsControlLibrary1
{
  public partial class UserControl1: UserControl
  {
    public UserControl1()
    {
      InitializeComponent();
    }
 
    private void button1_Click(object sender, EventArgs e)
    {
      OpenFileDialog ofdPic = new OpenFileDialog();
      ofdPic.Filter = "JPG(*.JPG;*.JPEG);gif文件(*.GIF);PNG(*.PNG)|*.jpg;*.jpeg;*.gif;*.png";
      ofdPic.FilterIndex = 1;
      ofdPic.RestoreDirectory = true;
      ofdPic.FileName = "";
      if (ofdPic.ShowDialog() == DialogResult.OK)
      {
        string sPicPaht = ofdPic.FileName.ToString();
        FileInfo fiPicInfo = new FileInfo(sPicPaht);
        long lPicLong = fiPicInfo.Length / 1024;
        string sPicName = fiPicInfo.Name;
        string sPicDirectory = fiPicInfo.Directory.ToString();
        string sPicDirectoryPath = fiPicInfo.DirectoryName;
        Bitmap bmPic = new Bitmap(sPicPaht);
        if (lPicLong > 400)
        {
          MessageBox.Show("此文件大小為" + lPicLong + "K；已超過最大限制的K范圍！");
        }
        else
        {
          Point ptLoction = new Point(bmPic.Size);
          if (ptLoction.X > picBox.Size.Width || ptLoction.Y > picBox.Size.Height)
          {
            picBox.SizeMode = PictureBoxSizeMode.Zoom;
          }
          else
          {
            picBox.SizeMode = PictureBoxSizeMode.CenterImage;
          }
        }
        picBox.LoadAsync(sPicPaht);
        lblName.Text = sPicName;
        lblLength.Text = lPicLong.ToString() + " KB";
        lblSize.Text = bmPic.Size.Width.ToString() + "×" + bmPic.Size.Height.ToString();
      }
 
    }
  }
}