Change variable during runtime - forms

Question

I have an enum:
type Tool =
| Rectangle = 0
| Circle = 1
And a variable to hold a enum value:
let mutable selectedTool : Tool = Tool.Rectangle
I have two buttons:
let btn (location:Point) (size:Size) =
let bt = new Button()
do bt.Location <- location
do bt.Size <- size
bt
// These badboys right here:
let rectangleButton = btn (Point(0, 0)) (Size(50,50))
let ellipseButton = btn (Point(50, 0)) (Size(50,50))
They each have an event connected to them:
let btnRectEvent = rectangleButton.Click.Add(fun(x) -> selectedTool <-Tool.Rectangle)
let btnElliEvent = ellipseButton.Click.Add(fun(x) -> selectedTool <- Tool.Circle)
I want my events to change the value of the selectedTool variable.
Currently, it doesen't work.
I then record my MouseDown event on my drawing area to draw a shape using this event:
let mouseEvent =
let x = selectedTool
form.MouseDown
|> Event.add ( fun (evArgs1) ->
if x = Tool.Circle then
graphics.Graphics.DrawEllipse(whitePen, evArgs1.X, evArgs1.Y, 15, 15)
else
graphics.Graphics.DrawRectangle(whitePen, evArgs1.X, evArgs1.Y, 15, 15)
form.Refresh())
form is running as follows:
form.Controls.Add(rectangleButton)
form.Controls.Add(ellipseButton)
form.Show()
while form.Created do
Application.DoEvents()
Bonus Question but not in need of answering:
Is it possible to catch a click event on the button, wait for a mousedown event on the drawing area, place the first corner of my shape, have a preview of the shape when I'm moving my mouse around, and set the second corner on mouseUp, in an not-too-overkill way?
TL;DR bonus question: Can I easily make the rectangledrawing work like in MSPaint?

Answer 1

So I spotted the problem:
when you do
let x = selectedTool
form.MouseDown
|> Event.add ( fun (evArgs1) ->
Something goes here
Inside the lambda x won't change. You probably want to either get rid of the let x = ... before the lambda or use a ref cell like this:
let selectedTool = ref Rectangle
then you assign with
selectedTool := Circle
and get the value with
if (!selectedTool) = Circle
Although a match would be more common - like so
form.MouseDown
|> Event.add ( fun (evArgs1) ->
match (!selectedTool) with
|Circle -> graphics.Graphics.DrawEllipse(whitePen, evArgs1.X, evArgs1.Y, 15, 15)
|Rectangle -> graphics.Graphics.DrawRectangle(whitePen, evArgs1.X, evArgs1.Y, 15,15)
form.Refresh())