C#_WinForms_OnPaint

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 MDI_zad2
{
    public partial class Form3 : Form
    {
        public Form3()
        {
            InitializeComponent();
        }

        private void Form3_Load(object sender, EventArgs e)
        {

        }

        protected override void OnPaint(PaintEventArgs e)
        {
            // Graphics g = e.Graphics;
            // Create string to draw.
            String drawString = "Stoyan Cheresharov";

            // Create font and brush.
            Font drawFont = new Font("Arial", 16);
            SolidBrush drawBrush = new SolidBrush(Color.Black);

            // Create point for upper-left corner of drawing.
            PointF drawPoint = new PointF(150.0F, 150.0F);

            // Draw string to screen.
            e.Graphics.DrawString(drawString, drawFont, drawBrush, drawPoint);

            // at any moment you can get the graphics object
            Graphics g = this.CreateGraphics();

            Pen blackPen = new Pen(Color.FromArgb(255, 0, 0, 0), 5);
            g.DrawRectangle(blackPen, 10, 10, 100, 50);


        }

        private void button1_Click(object sender, EventArgs e)
        {
            // it is going to be overwriten. It is not in OnPaint event
            Graphics g = this.CreateGraphics();
            // Create pen.
            Pen blackPen = new Pen(Color.Black, 3);

            // Create rectangle for ellipse.
            Rectangle rect = new Rectangle(0, 0, 200, 100);

            // Draw ellipse to screen.
            // e.Graphics.DrawEllipse(blackPen, rect);
            // but we are going to loose it when there is a window on top
            g.DrawEllipse(blackPen, rect);
        }
    }
}