C# OnPaint

要让窗体在载入的时候就显示图像必须重写OnPaint方法

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

        private void Form1_Load(object sender, EventArgs e)
        {

        }
        protected override void OnPaint(PaintEventArgs e)//重写OnPaint方法
        {
            base.OnPaint(e);//先执行基类的OnPaint方法
            Graphics g = e.Graphics;
            Pen p = new Pen(Color.Red);
            g.DrawEllipse(p, 40, 40, 100, 100);
            g.Dispose();
            p.Dispose();
        }
    }
}

这个程序执行结果就是

在窗体载入的时候会出现一个红色空心椭圆