Painting with System.Drawing.Graphics on form load

Question

I'm trying to draw a rectangle using System.Drawing.Graphics in C# Windows Forms, but I cannot seem to get it to work without using a button click event.

Searching online uncovered that I must use either the Paint or the Shown event within the form itself, however my attempts were unsuccessful.

I would like to run my Draw() method upon loading the form and its components.

public Form1()
{
    InitializeComponent();
    Draw(); //doesn't work
}

private void Draw()
{
    Graphics g = pictureBox.CreateGraphics();
    g.Clear(Color.White);
    Pen p = new Pen(Color.Black, 1);
    g.DrawRectangle(p, 0, 0, 50, 50);
}

private void ApproximateButton_Click(object sender, EventArgs e)
{
    Draw(); //works
}

What is the correct way of achieving this?

Don't forget to `.Dispose()` your `g` and `p` otherwise you'll end up crashing your app. — Enigmativity, Oct 11 '17 at 23:33

4D1C70 · Answer 1 · 2017-10-12T15:00:53.873

1

You can achieve this overriding the OnLoad event of Form, also you can reuse the PaintEvent parameter.

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);
    using (Graphics g = e.Graphics)
    {
        g.Clear(Color.White);
        using (Pen p = new Pen(Color.Black, 1))
        {
            g.DrawRectangle(p, 0, 0, 50, 50);
        }
    }
}

Edit: added using statement for disposing resources

edited Oct 12 '17 at 15:00

answered Oct 11 '17 at 23:31

4D1C70

490
3
10

2

You should properly show how to dispose the disposables. – Enigmativity Oct 12 '17 at 00:15
You likely will want to call `base.OnPaint(e)` first instead of last, or else the form may draw over whatever you just painted. – Scott Chamberlain Oct 12 '17 at 13:31
1

Thank you for your contribution, however this unfortunately didn't do it for me. I found the answer in a very similar question to mine, so I marked this question as a duplicate. You are still right about having to dispose the respective objects. – Ivan Spajić Oct 12 '17 at 16:38

score -1 · Answer 2 · answered Oct 12 '17 at 12:53

You also should be fine placing your function under Form1's Load event.

After subscribing for the Load event try this;

public Form1()
{
    InitializeComponent();
}

private void Form1_Load(object sender, EventArgs e)
{
    Draw();
}

private void Draw()
{
    Graphics g = pictureBox.CreateGraphics();
    g.Clear(Color.White);
    Pen p = new Pen(Color.Black, 1);
    g.DrawRectangle(p, 0, 0, 50, 50);
}

Load event is called after the constructor. Your form elements are being created in the constructor therefore you are having some problems trying to use them in the same function.

I tried this, and it does not work for me. I'm able to get a print confirming that I'm hitting the correct method delegated by the event, however upon calling my Draw() method, nothing happens. — Ivan Spajić, Oct 12 '17 at 16:06

Painting with System.Drawing.Graphics on form load

2 Answers2