Paint Event Handler

Question

I'm new to c# so that is probably the majority of my problem of not understanding how the paint event work. I have a code that paints a series of rectangles. I want to have it display using GDI+ when the space bar is pressed. I have everything working properly if I don't use the key event to call the drawing class. My problem is that when I put the new paint event handler into my spacebar event handler, nothing happens. I have removed some of my code to make it easier to see for the sake if this question. Thanks in advance.

using System;
using System.Windows.Forms;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.IO;
using System.Linq;
using System.Timers;
using System.Windows.Input;
using System.Threading;
using System.Threading.Tasks;
using System.ComponentModel;

public class Drawgra : Form
{
    public static void Main()
    {
       Application.Run(new Drawgra());
    }

    public Drawgra()
    {
        int screenheight = 950; int screenwidth = 1600;
        this.Size = new Size(screenwidth, screenheight);
        ConsoleKeyInfo key;
        key = Console.ReadKey(true);
        this.KeyPreview = true;
        this.KeyDown += new KeyEventHandler(Form1_KeyDown);
      //  this.Paint += new PaintEventHandler(Draw_outlines);
    }

    public void Form1_KeyDown(object sender, KeyEventArgs e)
    {
        if (e.KeyCode == Keys.Space)
        {
            this.Paint += new PaintEventHandler(Draw_outlines);
        }
    }



    public void Draw_outlines(object sender, PaintEventArgs e)
    {
        Graphics g = e.Graphics;
        Pen box = new Pen(Color.Black, 20);
        g.DrawRectangle(box, 100, 0, 200, 400);
    }

}//close form

Answer 1

You need add the event handler just once, not once per keystrike, then call Invalidate() on every keystroke to make it redraw and trigger the handler.