C# Graphics.Drawline function not working, “The name 'graphics' does not exist in the current context”

Question

I am creating my first visual C# program. I am trying to get to grips with drawing graphs/lines, however I am getting the error "the name 'graphics' does not exist in the current context".

This is the entirety of my program:

public Form1()
{

    InitializeComponent();

    Pen blackPen = new Pen(Color.Black, 3);

    Point point1 = new Point(100, 100);
    Point point2 = new Point(500, 100);

    graphics.DrawLine(blackPen, point1, point2);
}

Google tells me that the graphics.DrawLine function is within the System.Drawing namespace that I have already included.

Apologies if this is a simple question as this is very much my "hello world".

Answer 1

You could add an event handler to Paint event of the form, having code something like below:

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        Pen redPen = new Pen(Color.Red, 30);

        Point point1 = new Point(0, 0);
        Point point2 = new Point(500, 500);

        e.Graphics.DrawLine(redPen, point1, point2);

        redPen.Dispose();
    }

And not trying to do the drawing in the form constructor. So move the code from the constructor to this event handler.

Answer 2

You're probably working from examples you've seen online where the Graphics object is provided as a parameter to a method or defined outside of the code shown. Graphics objects can draw to a variety of targets--the screen, an image, a printer.... You should figure where you want your graphics to go; how to initialize or get a reference to the appropriate Graphics object will depend on this. For instance, if you want a simple way to draw to the screen, add a Paint event handler to a Form via the Windows Forms Designer. When the event fires, you'll get a PaintEventArgs object that has a property called Graphics . Use this to do your drawing.

Answer 3

You're declaring Graphics as a local variable within your constructor. You probably would rather declare it as an instance first, then assign it inside the constructor.

Answer 4

The issue appears to be that you haven't declared the graphics variable. I think you need something like:

public Form1() {
    InitializeComponent();

    Pen blackPen = new Pen(Color.Black, 3);

    Point point1 = new Point(100, 100);
    Point point2 = new Point(500, 100);

    Graphics graphics = CreateGraphics();
    graphics.DrawLine(blackPen, point1, point2);
}

The extra line here creates a new graphics object on the current form which you can use to draw the line.