How does the WinForms MouseWheel event work in F#? - winforms

Question

I want to figure out how the mouseWheel event works in the winforms library.
Though there is never any good examples to learn when it comes to F#
I hope one of you guys can tell me.
i was thinking something like this:
onMouseWheelEvent =
if MouseWheel event = scroll forward then
printfn "zooming in"
else
printfn "zooming out"
I know it is some silly code i am posting but i literally cant find anything on the winforms mousewheelevent other than it exists. How it works remains a mystery.
thanks in advance.

Answer 1

Try running this in f# interactive (courtesy of a similar example on fssnip from Tomas Petricek):
open System.Windows.Forms
// Create form, label and add label to form
let form = new Form(Text = "Scroller Test")
let label = new Label()
form.Controls.Add(label)
// register mousewheel event handler and capture scrolling
form.MouseWheel.Add(fun e ->
match e.Delta with
| n when n > 0 -> label.Text <- "Scrolled up"
| n when n < 0 -> label.Text <- "Scrolled down"
| _ -> ()) // making compiler happy even though e.Delta cannot be 0
// Show the form (in F# Interactive)
form.Show()

Answer 2

If you are using F# interactive, the simplest thing you can write to test how the MouseWheel event behaves is something like this:
open System.Windows.Forms
let frm = new Form(Visible=true)
frm.MouseWheel.Add(fun e ->
printfn "%A" e.Delta
)
When you select the code and send it to F# Interactive (Alt+Enter in most F# editors), you should see a form appear. When you then scroll, you'll see that Delta is negative or postivie number indicating how much up or down you scrolled.
If you want to run this as a standalone application, you'll need to display the numbers elsewhere (using a label, I guess) and you'll need to add Application.Run(frm) to the end to start the application.
I'd agree with Anton that WinForms is perhaps not what most people use for developing user interface applications these days, but I think that's not a problem - you can use WinForms to build perfectly fine applications and learn F#. The F# book I wrote some time ago has a bunch of WinForms examples.