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Validating Several TextBox Controls
f#

VS2008 with F# 2.0.0 (not that I would guess it matters).

I've got code similar to this for four textboxes I use to enter version information:

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let majorTextBox = new TextBox(Text = "1", Dock=defaultDockLocation, Width=defaultTextBoxWidth, TabIndex = 1)

majorTextBox.Validating.Add(fun cancelEvent ->

                cancelEvent.Cancel  <- not(ValidateVerField "^\d{1,6}$" majorTextBox.Text))

Hmm...can't seem to get the code tag to work right with the less than hyphen present.

At any rate, I've got four text boxes like that and all of them are pretty much the same--as far as the Validating event handler I mean. All four use a lambda and set the Cancel member within the lambda. As code smells go, that pretty much stinks to me. Huge violation of DRY. But I can't figure out the right combination to get the cancelEvent argument set correctly if it returns from a function.

I thought of trying this though I can't seem to get it to work:

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let validateVersion (eventArgs:System.Component.CancelEventArgs) (versionText:string) =

     new System.Component.CancelEventArgs (Cancel = not ValidateVerField (* etc. *)

Any suggestions?

By the way, I'm planning to start using Xaml--want to crawl before I try walking and I'm more familiar with WinForms.

.

I don't understand what you're asking.

Do you want something like

let addValidation (tb:TextBox) =
tb.Validating.Add(fun cancelEvent ->
cancelEvent.Cancel <- not(ValidateVerField yadda yadda))

addValidation majorTextBox
addValidation otherTextBox
...

?

By on 4/21/2010 10:50 AM ()

Hi Brian,

Yep--just tried it. You were right on the money.

It's hard to switch my thinking from the OO mindset (hang the same function on several objects) to the more FP approach (build one function to operate on several objects) but in this particular case your approach is obviously better than what I'd come up with.

Thanks again.

By on 4/23/2010 8:54 AM ()

For not understanding what I'm asking, Brian, you did pretty well. :-)

I think that's pretty much exactly what I need to do. As I said, four text boxes and I had the same validation code on all four. I've been at coding long enough to learn to hate the smell of duplicated code.

The thing that was confusing me was the cancelEvent eventargs object. I think your approach is pretty slick.

By on 4/21/2010 3:33 PM ()

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