Painting a rectangle

Question

I'm very new to windows form coding and I'm trying to make a minipaint which has three buttons (circle,rectangle and line) and when it gets a button as an input , it will draw the shape in panel. I have this shape class

class shape
{ 
   public Color color { get; set; }
   public int width { get; set; }
   public int startx { get; set; }
   public  int starty { get; set; }
}

which has color,width and start position properties.then I have this rectangle class for example:

class rectangle : shape
{
    int length { get; set; }
    int width { get; set; }  
}

which inherits the share properties from the shape class. now I want to print a rectangle in panel . I'm familiar with DrawRectangle method and I printed a rectangle as bellow:

Pen black = new Pen(Color.Black);
Rectangle rect = new Rectangle(20,20,400,200);
private void panel1_Paint(object sender, PaintEventArgs e)
{
    Graphics g = e.Graphics;
    g.DrawRectangle(black, rect);
}

but I don't know how to draw a rectangle from class rectangle:shape. I'm also having problem with assigning value from click button to rectangle. can you please help me?

You need to convert the MyRectangle to the generic Rectangle or just mash MyRectangle's values into an array of Points you calculate from your startx/y and it's lengths and use DrawPolygon. I would probably make a method in the MyRectangle.GetRectangle() that returns the System.Drawing.Rectangle — Poody, Nov 08 '16 at 07:06
should I make a draw method in rectangle class? something like " void draw() { System.Drawing.Rectangle(startx,starty,length,width); }" but this doesn't work — sara, Nov 08 '16 at 07:23
I believe that your definition of width in your shape class should most likely be thickness (so as not to get confused with width in your rectangle inherited class (and others). — Troy Mac1ure, Nov 08 '16 at 07:25
Take a look at the `Circle` class in [this example](http://stackoverflow.com/a/38347945/3110834) or the `IShape` interface and implementations in [this other example](http://stackoverflow.com/a/38749134/3110834). — Reza Aghaei, Nov 08 '16 at 10:29

Troy Mac1ure · Accepted Answer · 2016-11-08T07:50:26.490

1

May I suggest you have one draw function in your base class that each shape overrides.

    class shape
    {
        public Color color { get; set; }
        public int thickness { get; set; }
        public int startx { get; set; }
        public int starty { get; set; }

        public virtual void Draw(Graphics g)
        {
        }
    }

    class rectangle : shape
    {
        public int length { get; set; }
        public int width { get; set; }

        public override void Draw(Graphics g)
        {
            using (Pen pen = new Pen(color))
            {
                g.DrawRectangle(pen, new Rectangle(startx, starty, width, length));
            }
        }
    }

Then any shape can be drawn by calling .Draw(graphics). Define your rectangle:

        rectangle rectangle = new rectangle();
        rectangle.startx = 20;
        rectangle.starty = 20;
        rectangle.width = 400;
        rectangle.length = 200;

and then in your OnPaint (or wherever your are going to do it):

Graphics g = panel1.CreateGraphics();
rectangle.Draw(g);

The beauty of doing it this way is you can have a List and just iterate through them and draw each one once you have multiple shapes:

Graphics g = panel1.CreateGraphics();
foreach (shape s in shapes)          // Assuming shapes is List<shape>
    s.Draw(g);

edited Nov 08 '16 at 07:50

answered Nov 08 '16 at 07:29

Troy Mac1ure

637
4
9

thank you so much for that. but how am I suppose to call this on my panel? – sara Nov 08 '16 at 07:39
Get the Graphics for your panel such as: Graphics g = panel1.CreateGraphics(); and then pass that to your shape draw function. After creating a rectangle named rect1 for example, you can then just call rect1.Draw(g); to draw it to your panel1 – Troy Mac1ure Nov 08 '16 at 07:43
it doesn't recognize rectangle.Draw(g) in panel1_paint :( – sara Nov 08 '16 at 08:11
You will have to declare your variable globally to access it anywhere within the class, not within a function. – Troy Mac1ure Nov 08 '16 at 08:57
2

@sara Do not use CreateGraphics. Use the panel's paint event where the Graphics are supplied in the `e` parameter. CreateGraphics is a temporary drawing, easily erased by minimizing and restoring the form, etc. – LarsTech Nov 08 '16 at 16:44

score 1 · Answer 2 · answered Nov 08 '16 at 07:31

The following code allows you to drag and draw a Rectangle on a PictureBox. The conversion is implemented in MyRectangle. I also used slightly different properties.

public class Shape
{
    public Color color { get; set; }
    public Point origin { get; set; }
}

public class MyRectangle : Shape
{
    public Size size { get; set; }

    public Rectangle ToRectangle()
    {
        return new Rectangle(origin, size);
    }
}

public partial class Form1 : Form
{
    Point mouseDownPoint;

    public Form1()
    {
        InitializeComponent();
    }

    private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
    {
        mouseDownPoint = e.Location;
    }

    private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
    {
        MyRectangle rect = new MyRectangle();
        rect.origin = mouseDownPoint;
        rect.size = Size.Subtract((Size)e.Location, (Size)mouseDownPoint);

        pictureBox1.CreateGraphics().DrawRectangle(new Pen(Brushes.Black), rect.ToRectangle());
    }
}

And maybe consider using PascalCase for class names. (Shape instead of shape)

Painting a rectangle

2 Answers2