C# Line Painting Problems

Question

I need help drawing a line on a WinForm.

The code I currently have is mostly pulled off of MSDN:

using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

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

    private void Form1_Load(object sender, EventArgs e)
    {
        this.Invalidate();
    }
    private void Form1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
    {

        // Insert code to paint the form here.
        Pen pen = new Pen(Color.FromArgb(255, 0, 0, 0));
        e.Graphics.DrawLine(pen, 10, 10, 300, 200);
    }
}

}

Currently, this code does not draw anything at all.

Answer 1

Your code, as posted, is fine. It renders a black line in the middle of the form:

I suspect your problem is you don't have the form's Paint event subscribing to your Form1_Paint method. You can't just put this method there and expect it to get called magically.

You can fix that by adding it to your Form's constructor:

public Form1()
{
    InitializeComponent();
    this.Paint += Form1_Paint;
}

Alternatively, you can do this in the designer, which does the same event subscription, it just tucks it away inside of InitializeComponent().