Question

i have a program like this

let form = new Form()
let drawArea = new Panel(Location = new Point(200,0), Height = 600, Width = 800)
let rectBrush = new SolidBrush(Color.Blue)
form.Controls.Add(drawArea)

drawArea.MouseClick.Add(fun args -> 
    drawArea.Paint.Add(fun e -> 
        e.Graphics.FillRectangle(rectBrush, args.X, args.Y, 50, 50)))

Application.Run(form)

so when i click a blue rectangle appears. However, where are these rectangles stored? is there any way to retrive a list of all the rectangles being part of the “drawArea”?

Otherwise, is there a way to add rectangles as child controllers to a panel or simular winform object?

Thank you

Answer 1

I don’t know of a way to retrieve these rectangles that way.

The best you can do is make a Rectangle class, and make it inherit from Control or UserControl. Then override it’s protected OnPaint(…) method. For example:

public class FilledRectangle : UserControl
{
     private readonly float x, y, w, h;
     // also the brush here

     public FilledRectangle(float x, float y, float w, float h)
     {
          this.x = x;
          // ...
     }

     protected override void OnPaint(PaintEventArgs e) // not sure about the event args type name
     {
          e.Graphics.FillRectangle(this.myBrush, this.x, this.y, this.w, this.h);
     }
}

Now you can simple add an object of this type to the Controls collection like so:

Controls.Add(new FilledRectangle(...));

With this approach you can easily create a collection of the rectangle objects and make them behave like you want them to.

Note that the examples I wrote above are in C#, but it shouldn’t be too difficult to port it to F#. Only reason I’m not doing it is because I’m not very familiar with its syntax. Your question is not F#-specific, but .NET-specific.

Also note that as it has been commented by Hans, the Paint event won’t fire until you call Invalidate().