Question

I am translating a C# project into F#. While the logic part is easy, I am confused with the GUI part:

public partial class GomokuGUI : Form {
    private void GomokuGUI_Load(object sender, EventArgs e)
    {
        this.Width = 500;
        this.Height = 550;
        ...
        this.Paint += new PaintEventHandler(GomokuGUI_Paint);
        Graphics gp = this.CreateGraphics();
        DrawChessbord(gp); 
    }

    private void GomokuGUI_Paint(object sender, PaintEventArgs e)
    {
        Graphics gp = e.Graphics;
        DrawChessbord(gp);
    }

    void DrawChessbord(Graphics gp)
    {
        float w, h;
        SolidBrush br = new SolidBrush(linecolor);
        Pen p = new Pen(br, frame);
        gp.DrawLine(p, 20, 45, this.Width - 25, 45);
  ...
    }

   private void Form1_Click(object sender, EventArgs e) {
          Graphics gp = this.CreateGraphics();
                DrawChess(gp);
     ...
}
}

Problem: How to write above C# code in F#…Thanks

Answer 1

Note that F# doesn’t have any WinForms designer, so if you have some controls in the Form, you’ll need to create them manually (alternatively you can design the form in C#, compile it and reference it from F#). You could start with something like this:

type GomokuGUI() as this =
  inherit Form(Width = 300, Height = 550)

  let DrawChessbord (gp:Graphics) =
    let br = new SolidBrush(linecolor)
    let p = new Pen(br, frame)
    gp.DrawLine(p, 20, 45, this.Width - 25, 45)
    // ...

  let paintGui (e:PaintEventArgs) =
    let gp = e.Graphics
    DrawChessbord(gp)

  do 
    this.Paint.Add(paintGui)
    this.Click.Add(fun _ ->
      let gp = this.CreateGraphics()
      DrawChess(gp) 
      (* ... *) )

It uses a couple of interesting things:

• You can specify some parameters such as Width and Height in the constructor when calling the base class constructor.
• You need to use as this in the class declaration, so that you can refer to the class in the do code (which is run during construction)
• You can use Add to register event handler and you can either give it a named function (e.g. patinGui) or a lambda function if you need to do only some simple call (e.g. handling of Click)